Field Engineering Education Student Self-Study Course

IBM Confidential Field Engineering Education Student Self-Study Course

IBM Confidential

This document contains information of a proprietary nature. ALL INFORMATION CONTAINED HEREIN SHALL BE KEPT IN CONFI­ DENCE. None of this information shall be divulged to persons other than: IBM employees authorized by the nature of their duties to receive such information or individuals or organizations authorized by the Field Engineering Division in accordance with existing policy regarding release of company information.

Introduction to Teleprocessing PREFACE

This course is provided to acquaint Customer Engineers with some of the important concepts of Teleprocessing which differ from those of usual Data Processing.

Address comments concerning the contents of this publication to: ffiM Corporation, Field Engineering Education, Dept. 911, Poughkeepsie, N. Y. 12602

IBM CONFIDENTIAL CONTENTS

SESSION I, INTRODUCTION. 5 Shift Registers. . . . . • • • 43 IBM Teleprocessing 5 Shift Register - Transmit 43 Review Questions ...... 10 Shift Register - Receive 45 Review Questions...... 50 SESSION 2, COMMUNICATION CONCEPTS 11 Review Questions •...... 15 SESSION 7, IBM LINE ADAPTER 51 Review Questions. . . . . • • . • 53 SESSION 3, DATA TRANSMISSION 17 Review Questions ..•..•.• 21 SESSION 8, DATA CONTROL OF MODEMS (DATA SETS) .• 55 SESSION 4, COMMUNICATIONS CHANNELS 23 Bi-Polar Mode •• 55 Types of Channels • • 25 Uni - Polar Mode 55 Signaling Methods 26 Current Mode 55 Frequency Spectrum 28 Review Questions . 56 Carrier Systems . . • 28 Modulation. . . . . • 29 SESSION 9, COMMUNICATIONS FACILITIES 57 Grades of Channels 30 Communications Common Carriers ... 57 Broad Band Channels 30 The Federal Communications Commission . • 57 Voice Grade Channels • 30 State Utility Commission •..••••• 58 Subvoice Grade Channels. 31 The International Telecommunications Union 58 Telegraph Grade Channels 31 The Bell System. . • • • • • • • . . • • • 58 Line Quality . . • • . 31 General Telephone and Electronics Corporation • 59 Data Sets •••••• 32 Independent Telephone Companies • . . • 59 Reference Sources 34 Western Union. . • • • • • . . • . • • 59 Review Questions. . • 35 American Cable and Radio Corporation. 60 RCA Communications, Inc. . . . • . • • 60 SESSION 5, COMMUNICATIONS SYST EM CONTROL • 37 Privately Owned Communications Systems • 61 Message Switching .•...• 38 Review Questions . • • . • • . • • . • 62 Manual Torn-tape Switching 38 Semi-automatic Switching 38 APPENDIX - TELEPROCESSING GLOSSARY • 63 Automatic Switching. . . • 38 Circuit Switching. . • . . . 38 ANSWERS TO REVIEW QUESTIONS 88 Selective Calling and Polling 38 Session 1 88 Line Control . 38 Session 2 • 88 Intercept. 39 Session 3 • 88 Editing .. 39 Session 4 • 89 Priorities 39 Session 5 • 89 Logging . 39 Session 6 90 Error Control. 39 Session 7 • 90 Terminal Operating Modes. 39 Session 8 90 Review Questions. . • . . . • 40 Session 9 90

SESSION 6, IMPLEMENTATION 41 SERD ES and Shift Registers 41 Transmit Operation 42 Receive Operation. . . 43

IBM CONFIDENTIAL

SESSION 1

INTRODUCTION

In this session, you should learn why the field of Teleprocessing exists, how IBM has contributed to its growth, and how a typical system is configured.

Highlights

• Teleprocessing provides a means of obtaining timely, accurate reporting of informa­ tion with reduced time, effort, and expense. o Since 1941, IBM developments have increased transmission rates of data from three cards per minute to approximately 20,000 card equivalents per minute. o Future of Teleprocessing is as unlimited as human imagination. • Existing Telephone and Telegraph facilities feed information to computers.

The history of data communications can be IBM TELEPROCESSING traced back to biblical times. The Book of Esther relates that the delivery of orders from King IBM's first development in this field was the intro­ Ahasuerus to his provincial governors involved a duction, in 1941, of the IBM 057 and IBM 040. Fig­ delay of eleven months. Later, history states that ure 1 traces the necessary operations: the author Aeneas described a system, used during First, the cards were processed through the 057 war, in which a 5 x 5 matrix and a display of torches and the data punched into paper tape. This involved were used to indicate coordinates of the letter de­ handling the cards twice. Next, the paper tape had sired. By the 15th century, a postal system had to be removed and transferred to a telegraphic type been introduced in France by which the use of relay reader for transmission. At the receiving location, teams speeded the communication of the written the paper tape was transferred from the telegraph form. Paul Revere's lantern signals and Reuter's perforator to the 040 to generate punched cards. carrier pigeons were steps in the development of The procedure required intervention at points A, B, communications systems which led finally to the C, D, E, and F. When the cards were converted to land and overseas telegraph. The telegraph, fol­ tape, the maximum rate of transmission was about lowed by the telephone and radio, has made possible three cards per minute. Today, the IBM 063 and data communication as we know it today, and the IBM 047 perform corresponding functions. In this field of Teleprocessing. ' publication, the term "cards per minute" re'furStO With the increasing complexity of business, the 80-column punched IBM cards. need of management for up-to-date information has To reduce the manual intervention required, the outgrown the facilities of normal postal services, IBM Card Data Transceiver was introduced in 1954. even air mail. The present need is for centralized, This equipment allows several configurations (see immediately accessible information on diverse oper­ Figure 2): printing or nonprinting card reader ations. Teleprocessing takes a giant step toward punches can be used on either telephone or telegraph fulfilling this need. The specific objectives of Tele­ facilities. With the IBM 67 Telegraph Signal Unit, processing are: three transmission rates are possible: 60, 75, or 1. To provide rapid transfer of information from 100 words per minute., This corresponds approxi­ the source to the data processing location. mately to 3, 4, or 5 cards per minute, respectively. 2. To provide accurate and timely reports for Transmission of 10 to 12 cards per minute is possi­ management information and decision making. ble' using the IBM 068 Telephone Signal Unit, de­ 3. To accomplish the foregoing with reduced pending on whether the 066 or 065 punching unit is effort, time, and expense. employed. Note that intervention is now necessary

IBM CONFIDENTIA L 5 Encoder Paper Tape Card Reader {Translator} Punch

... 057 ~ 1 !

, ...... ~ 1 j

Tape Reader Telegraph Paper Tape L Distributor System Punch 0 8 1

...... --J l 1

Paper Tape Translator Card Punch Reader Decoder

~'------040

FIGURE 1. FIRST IBM TELEPROCESSING

6 IBM CONFIDENTIAL 065/066 I (; (; I 067/068 ~-"7"'--=:--~ Reader I .2 067/068 i :Reader 1-----, I § Signal Unit Telegraph or Signal Unit C I I .= Telephone Lines .=

FIGURE 2. IBM CARD DATA TRANSCEIVER only at points A and B of Figure 2. the STR family, the 7710 provides the capability of Recent additions to data terminal equipment in- connecting two computers, and transferring data clude the IBM 357 Data Collection System, the IBM from the memory of one to the memory of the other 1001 Data Transmission System, and the IBM 1013 through communications facilities. Figure 3 shows Card Transmission Terminal. The 1013 features one method of connecting this unit for actual opera­ transmission between terminals which operate in tion between two 1401's, and the corresponding constant synchronism with each other through the communications line facility. use of an STR unit. (Synchronous Transmitter­ In late 1964, the IBM 7711 Data Communications Receiver). With the development of the STR, we Unit was introduced. This provided for connection can transmit data at speeds not previously possible. of a 729 or 7330 tape unit to a communications net­ We next consider the IBM 7701 and 7702 Magnetic work. It made possible the transmission of data Tape Transmission Terminals utilizing the STR con­ over a communications facility at very high speed cept for data transmission. The 7702 can send and by a method similar to that of the 7710, without receive data at 300 characters per second. Convert­ tying up the customer's computer system. The cur­ ing this to cards per minute, we can compare the rent maximum data rate is 28,800 characters per change in transmission rate with that of the trans­ second. ceiver. The following formula is used: With System/360, the requirements for Tele­

Cards per minute: = characters per second x 60 seconds per minute processing are multiplied tremendously. Complex 80 characters (columns) per card systems have enormous appetites for data and must be fed to realize their full capabilities. For opera­ For the 7702, we obtain an answer of 225 cards per tion in this area, we have the 2701, 2702, 2703. minute - which is quite a change since the trans­ We shall examine the individual capabilities of Sys­ ceiver. tem/360 working with these new devices. First, More recently, the IBM 7710 Data Communica­ consider the 2701, because it accommodates most of tions Unit has been introduced. Also a member of the requirements previously outlined. The 2701

1401 1401 nlO 14----~ Data Data 14----~ n10 Set Set Telephone Lines

FIGURE 3. IBM nlO DATA TRANSMISSION SYSTEM

IBM CONFIDENTIAL 7 Data Adapter Unit has the ability, through the use of the remote terminals. He can now combine the low­ appropriate adapters, to service data terminal de­ speed networks for transmission on one higher speed vices operating in the telegraphic range of 60 words telephone channel. Figure 4 shows an example of per minute to high speed graphic display units oper­ the configuration. ating at 1.1 million bytes per second. For example: We can consider some more specialized applica­ 1. Telegraphic adapters exist that operate with tions of Teleprocessing. The IBM 7770 and 7772 60, 66, 75, and 100 word per minute telegraph provide voice answer back capability in response to terminals, such as those encountered on existing digital inquiries to a computer system. The IBM networks. 2260 and 2848 are available to provide low cost, 2. Terminal adapters are available for opera­ quiet, efficient inquiry to computers, and visual tion with networks of IBM 1030, 1050, 1060 or 1070 display of responses. This brings us up-to-date on terminals. These can operate over switchable tele­ the history of Teleprocessing in IBM and leads us to phone facilities with interfacing equipment provided the future. by the common carriers (communication companies), Accurate high-speed transmission of data be­ or over the customer-owned or leased line facilities tween various locations is an extremely challenging with the IBM Line Adapter acting as an interfacing problem. Some immediately foreseeable applications . device. Interface is the common boundary which are: exists when lines pass from one unit to another, or 1. Recording at point of sale with immediate from one service to another. When the character­ connection to a banking facility for account adjust­ istics of a signal on one side of the interface is dif­ ment ferent from that required on the other side of the 2. Direct digital recording of remote data in a interface, some kind of interface conversion device computer system from any telephone must be used. 3. Time-controlled automatic meter reading 3. For high speed data transmission and com­ 4. Optical scanning of cash register sales and/ patibility with other members of the STR family, the or daily record tapes Synchronous Data Adapter (SDA) may be used with 5. Vehicle traffic control and air traffic control the 2701 to provide data rates up to 28,800 charac­ (perhaps even space traffic control) ters per sec.ond. 4. The 2701 may also transfer data from a Without applications such as these, the need for System/360 to a graphic plotter or similar display complex high-speed ultra reliable computer systems device, through the Parallel Data Adapter (PDA). diminishes. New applications will require a vast Data rates are limited only by the speed of the amount of work in establishing world-wide compati­ processor (in the case of a high-speed Selector bility standards of services and methods. Electronic channel, 1. 1 million bytes per second in groups of Industries Association (EIA) domestically and the 2 to 16 bytes at a time). In a Teleprocessing envi'­ Comite' Consultatit International Telegraphique et ronment, the 2701 can handle signals from a maxi­ Telephonique (CCITT) in Europe have already done mum of four telephone and/or telegraph lines; can a great amount of work in these areas. Continued automatically dial the telephone number of the re­ association and cooperation in these endeavors will mote terminals, or operate with selective call or help eliminate confusion in this growing science and automatic call telegraph terminals. Customers re­ provide a sound basis for future developments. quiring interface with more than four telephone or The future promises many new applications such telegraph lines, at transmission rates less than 180 as data transmission for coordinating the space ex­ bits per second, may select the 2702 or 2703. The ploration effort. A trip to the moon requires many 2702 can control 31 channels or lines while the 2703 days, but radio communication requires only about can control a maximum of 176 channels or lines. one second. It can readily be seen that demands for Note that, if we were employing 1050 terminals on TP will expand fantastically. We have already seen this line, there could be a maximum of 26 terminals the use of telemetry methods employed for examin­ on each of the 176 lines. Now we are dealing with a ing the surface of Mars and we realize that this is practical application utilizing the maximum capabil­ only a beginning of a vast series of extra-terrestrial ity of a Teleprocessing system. More information applications. To talk about applications in the more concerning the configuration possibilities of the 2703 immediate future, we will have only to consider the appears later in this course. transmission facilities which have just been made Since the announcement of the 2701, 2702, 2703, available for worldwide TP through the synchronous a new device called 2712 Remote Multiplexor has communications satellites, such as Early Bird. been added to the line. A customer previously re­ Remember that the primary aim of TP is more quired up to 14 separate telegraph or 10 telephone effective business operations through outstanding lines between the data processing center (DPC) and service to customers . Having examined the past,

8 IBM CONFIDENTIAL High Speed Communication Line Remote Multiplexor

3 2 4 1\/ f- 2702 2712 f-}'t- Multiplexor 5 6 10 f := To Terminals Channel 7 8 29 } Communications Lines to Terminals ~ Low Speed Line 30 Ex; 1030, 1050,1060,1070,2741, Teletypewriters t-

Local 360 CPU 2 2701 Data Collection Terminals DAU 3

Selector Channel Long Distance

Terminal Data Communication 40 Feet or Less 1 Terminals

2 2701 1--'2=--______--1 .. Process Control Terminals DAU 3 High Speed Synchronous (e.g., 2701 on another Data System /360 CPU) Device

FIGURE 4. SYSTEM /360 TELEPROCESSING

present, and future, we will look at the Teleprocess­ questions, you may proceed with Session 2. If you ing application, and the various concepts and ser­ answer any questions incorrectly, you should review vices required to implement it. the appropriate portions of the text before proceed­ This completes Session 1 of this course. If you ing. can correctly answer all of the following review

IBM CONFIDENTIAL 9 REVIEW QUESTIONS cards per minute? (For the purposes of the question, ignore any delays due to answer back or error pro­ 1. When did IBM enter the field of Teleprocess­ cedures.) cards per minute. ing? 7. The four general types of remote terminals 2. What are the three objects of Teleprocessing? through which a System/360 Computer may commun­ icate, using an IBM 2701 Data Adapter Unit, are:

______and ______3. What existing communications facility pro­ 8. If you wanted a remote terminal from which vided the connecting link between IBM Card Trans­ you could interrogate a computer, and receive ceivers using type: answers on a television-type display, which IBM 068 Signal Units? ______Teleprocessing Terminals would you select? ____ 067 Signal Units?______4. What are the three transmission rates in 9. Which IBM Teleprocessing devices are cap­ Words p~r Minute when utilizing the IBM Card Data able of answering an inquiry with voice responses? Transceiver with an 067 Signal Unit? ______and ______5. If a Word is equal to six characters, and 10. Draw a diagram showing how a System/360 each IBM Card Data Transceiver Character is made computer could be connected to five terminals of the up of 8 possible bits, what would be the transmission IBM 1050 type, where three of the terminals are in rates of question #4 in terms of Bits per Second? the same building with the computer and two are lo­ ______~_and cated apprOximately 5 miles away. You are limited in this problem to using communications facilities 6. What is the approximate maxi?lum transmis­ that the customer already has installed and further, sion rate of the IBM 7711 Data Communications Unit each of the terminals must be able to communicate handling magnetic tape if we express it in terms of with the others.

10 IBM CONFIDENTIAL SESSION 2

COMMUNICA TION CONCEPTS

As a result of completing this session you should: 1. Become familiar with the important factors to be considered in Communication System design. 2. Learn how to represent a system diagrammatically. 3. Learn how one type of customer utilizes these services. 4. Be able to define Teleprocessing.

Highlights

• Design factors: Purpose, number and size of messages, priority of messages, accuracy and cost. • Network: System of devices capable of intercommunication according to certain rules. • Teleprocessing provides our customer with a way to improve service to their cus­ tomers and, at the same time, improve their own operating efficiency. o Airline Reservation System remote terminal hookup to Data Processing center. o Teleprocessing defined.

The history of rapid communications from Before we discuss the individual pieces of equip­ smoke signals to sattellites reflects the continual ment that make up the Teleprocessing data commun­ growth in man's ability to convey information be­ ications system, we should define "network". The yond the range of the human voice. In less than a network describes the entire connection of the re­ hundred years, the electrical communications in­ mote terminal eqUipment and the intermediate proc­ dustry has developed from the first manually-keyed essing equipment and, finally, its connection to the telegraph to complex television systems. Messages data processing center to perform all of the functions have been sent and received over a million miles of of this system. The various remote devices and space, and television programs have been trans­ intermediate devices are connected to the data proc­ mitted from the United States to Europe by way of a essing center in the main office over telephone lines communications satellite. With all of these techno­ or perhaps dial-up telephone facilities or telegraphic logical advances, the basic considerations in a facilities. Figure. 5 shows three basic types of modern communication system are not too different network. The network at A represents a single drop­ from those in a primitive society using drums or type - that is, there is only one remote terminal smoke signals to send messages between related working with one control station. In any network, we villages. have to define one location as the control station so Some of the imnortant factors which must be that it can set up the necessary controls for the considered in communication system design are: entire communications network. Note that in network B, there are three terminals. At the extreme left­ 1. The purpose of the communication system hand side, (the apex of the triangular arrangement) 2. The number and size of the messages Station 1 could be the control station. Each remote 3. The priority of the messages terminal operates with the control station and is not 4. The accuracy and cost of the system capable of directly communicating with the other The following description of a data communication sys­ except through the control station. In Figure C, we tem introduces some of the terms and illustrates the note that all three t~rminals or stations are connect­ scope of the material covered in succeeding sessions. ed together. Thus, terminal 1 can communicate

IBM CONFIDENTIAL 11 2 2 (e) Arranging for wheelchairs, etc. to meet arri ving passengers who may require them 2. Improved airline efficiency thru: (a) Timely maintenance scheduling (b) Fewer unused seats on flying aircraft o 0 (c) Accurate crew time-logging A 2 3 C 3 (d) Advance weather information accurately logged and constantly available FIGURE 5. BASIC NETWORKS (e) Accurate control of arrival and departure of aircraft The concept of networks, as applied to the Airline Reservation System, is shown in Figure 6. The Airline Reservation System consists of a data processing center (DPC). This DPC contains computing equipment including disc files, drum files, and tapes for both long and short...;.term storage with terminal 2, 2 with 3, or 3 with 1, each indepen­ depending on the speed of access rate required. In dent of the other. Networks Band C are represen­ addition, there are special devices known as multi­ tative multidrop networks, since the control station plexors to coordinate the operations of the duplicate works with more than one other terminal. devices located in the DPC. The connecting lines between these terminals The DPC is connected to strategically located represent the communication channel or circuit terminal interchanges on high-speed telephone lines . . (also called lines). This channel or circuit can be There may be as many as 30 terminal interchanges a wire, or a cable, or it can be a radio or micro­ on one line. (We will use the abbreviation TI to wave link. To review what we have learned about represent a terminal interchange.) Through lower networks: speed channels, each of these terminal interchanges In the figure at A, terminal 1 may communicate may be connected to 30 "agents' sets". Agents' Sets with terminal 2. In the figure at B, terminal 1 can are the individual reservation terminals of the sys­ communicate with 2 or with 3. However, if terminal tem. The agent sets cannot communicate directly 3 wishes to communicate with 2, it must first com­ with each other but they may communicate through municate with terminal 1. Terminal 1 may then re­ the DPC under program control. The agent sets are lay the message to terminal 2. Here we have an normally installed in locations such as travel bureaus, ideal example of "Message Switching". The message ticket-selling agencies, or airports. The agent sets must first be sent from 3 to 1, then rerouted from send messages to the terminal interchange. The TI 1 to 2. In the Figure at C, we find that terminals 1, stores these low-speed messages and then transmits 2 and 3 may each communicate directly without re­ them in groups (soon after they are received) over quiring another station to perform any switching the high-speed telephone line for maximum efficiency function for them. The process by which the desired of transmission. Now, consider the matter of num­ terminal receives or transmits the message is ber and size of messages. analogous to the concept of circuit switching opera­ The agent set consists of equipment which can tion. More about circuit switching and message send and receive prearranged fixed code sequence switching appears in later Sessions. messages as well as operator-controlled texts. The In summary, the four main factors to be consid­ relative sizes of these messages are: ered in a communication system design are: purpose, 1. The fixed-length messages -- these are nor­ number and size of messages; priority or urgency mally 11 characters in length. of messages; the accuracy of the system; and cost 2. Variable-text messages -- approximately 100 of the system. The Airlines Reservation System character blocks. Additional blocks may be used handles some of these factors in the following man­ but they require special considerations either by the ner: TI or by the DPC. 1. Improved customer service through: The agent set can handle only one message at a (a) Reliable reservation control time. It can send or receive, but not simultaneously. (b) Advance hotel reservations for passen­ This is called a "half-duplex" operation. We will gers cover the half-duplex concept again later. Remem­ (c) Advance car rental arrangements at ber that half-duplex means the ability to send or to destination receive as long as we don't try to do both at the (d) Special dietary instructions if necessary same time.

12 IBM CONFIDENTIA L e co U .gE -0 c: a o f-

TI = Terminal Interchange AS = Agents Set Terminal

FIGURE 6. AIRLINE RESERVATION SYSTEM

The TI can be operating with as many as 30 of that it's time to 'start the poll of all of the terminal these agent sets. All these agent sets could con­ interchanges over again ("Poll" is the term meaning ceivably send at t~e same time, but the terminal "invitation to transmit" ). Only once does the data interchange has the capability to so sample the in­ processing center have to send out a specific com­ coming lines that it will never miss information mand to transmit to a terminal interchange, and then coming from the agent sets even if all transmit only to the first terminal interchange in the list. simultaneously. The terminal interchange can store From then on, as each terminal interchange finishes up to 39 individual message segments, each message sending its own blocks of traffic, it tells the next TI segment consisting of as many as 100 characters. down the line to send. This is the most efficient These may be any combination of messages destined way to handle this type operation. for the DPC, or return messages from the DPC in­ Now let's examine the problem of urgency of tended for agent sets. messages. As can be seen from the preceding para­ The manner in which the terminal interchange graph, the urgency of messages is established only communicates with the data processing center is by the DPC. The DPC can cause a change in the variable: that is, it may either be based on a re­ sequence in which the terminal interchanges are per­ quest from the DPC to transmit or it may be based mitted to communicate with it. Thus, we can alter on a previously received "go-ahead" signal from that sequential pattern of one terminal interchange another' terminal interchange. This perhaps seems telling the next down line terminal interchange to a bit confusing; but if we consider that on any high­ transmit. speed line there may be as many as 30 of these ter­ minal interchanges, each serving 30 agent sets, it is For example, consider Figure 6, communication obvious that the most efficient way to handle this line H. On this communication line, we have ter­ operation is for each terminal interchange to say, minal interchanges 1, 2, 3, 4 and 5. From terminal "Well, I'm done sending my traffic to the DPC, next interchange 3, note that we have agent sets connected. man down the line pick up the ball and carry it. " The line that is shown (with the breaks) represents This is the way it is done in some systems. Thus, the entire 30 agent sets that could be connected to when a complete line of terminal interchanges has terminal interchange 3. Suppose while transmitting sent all of its messages to the DPC, and finally, the from terminal interchange 1, the data processing last one says, "Go ahead, DPC", the DPC lmows center in scanning its polling charts finds that on a

IBM CONFIDENTIAL 13 normal basis, at this time of day, terminal inter­ accuracy are also important factors for consideration. change 4 will be piling up a lot more messages than The completed network must be examined and con­ it can possibly handle. The DPC can send a message sidered relative to its purpose, the volume of work, called a "change next interchange address" message the required response times and, finally, in terms to terminal interchange 1 which will cause terminal of cost. While cost is important, it is extremely interchange 1 to tell terminal interchange 4 to go unwise to attempt to plan a network based on meeting ahead instead of 2. This method of changing the a pre-established price. This -course will not deal polling sequence permits maximum utilization of with specific costs of facilities or equipment but the network facilities. The configuration of the network customer engineer should be aware that this is an can vary considerably from that shown in Figure 6. important consideration. Publications, covering The following particulars could vary, depending upon detail cost of required services, are available from the need for capacity and the demand for accuracy various common carrier companies, the Federal of the particular system: Communications Commission, and some state utility 1. Number of lines commissions. These are called "Tariffs," and 2. Number of terminal interchanges per line represent the standard prices charged for given 3. Number of agent sets per line into the ter­ services. minal interchanges This completes the self-study portion of text for 4. Complexity of the computing portion of the Session 2. Additional information on any of the DPC initial concepts presented here, can be found in the Let's talk a little more about this problem of following publications: accuracy and cost. To eliminate errors, many checks are made as the data is handled. Some of 1. Data Communications, Form 320-0903. This book is a detailed review of the development and these are: application of Teleprocessing equipment in IBM. 1. Each character sent from or received by the 2. Reference Manual IBM 9000 Series Airline agent set is parity checked Reservation Systems Remote Equipment, Form 2. Each character received by the terminal A22-6640. interchange is parity checked 3. Teleprocessing Systems Summary, Form 3. Each message is checked for a specific count A24-3090. This book will outline the basic char­ agreement on transfer between the terminal inter­ acteristics of many of the Teleprocessing devices change and the data processing center. Any disa­ marketed by IBM. greement in the count constitutes an error some­ where in the message. At this point, you have probably derived a defini­ Communication facilities are available to cover tion of Teleprocessing. Teleprocessing as it con­ the entire range from fast to slow • Microwave cerns IBM designates IBM products used for trans­ channels can carry great amounts of information mitting and receiving data at separately located data quickly but are considerably more expensive than a processing offices. Teleprocessing equipment con­ relatively slow, telegraph-rate, channel. Depending sists of transmitting terminals and receiving termi­ upqn customer requirements, the Airline Reserva­ nals that utilize transmission facilities such as tion System agent set may use telegraph facilities telegraph lines, telephone lines, and microwave or some type of telephone channels. Between the radio signals. terminal interchange and DPC, transmission occurs The next section of this course consists of study at about 3 milliseconds per character. This requires questions. for review to find out how much you learned higher speed telephone-type channels. In order from what you read, and how well you understand the satisfactorily to establish a cost for the system, a principles presented. cus~omer m~st weigh the advantages of the system If you can answer the following review questions against not having the system. The most efficient correctly, you may go on to Session 3. If you answer configurations and the most economical communi­ any questions incorrectly, review the appropriate cation channel consistent with required data rate and sections of the text before proceeding.

14 IBM CONFIDENTIAL REVIEW QUESTIONS:

1. The four main factors to be considered in the design of a communication system are: (a) ______(b) ______(c) ______(d) ______2. (a) Utilizing the principles of Figure 5, draw a similar schematic representation of 3. When the terminals of DPC-B wish to com­ the network consisting of a large Data Proc­ municate with each other, is Message Switching or essing Center (DPC) connected to two smaller Circuit Switching utilized, as configured in question DPCs (A & B). Each of the small DPCs is #2 (a)? ______connected with its own network of five remote ~)?------terminal devices. Each of the terminal de­ 4. The terminal systems of question #2a would be vices on either DPC-A or DPC-B is capable considered as of communicating with any other terminal but (a) Single drop only through one or more of the DPCs. ~) Multi -drop 5. A multiplexor coordinates the operation of multiple devices utilizing shared facilities. (True, False) 6.· How many Agents sets could be serviced on one high-speed telephone line if the maximum number of terminal interchanges was employed?

70 List four areas in which the Airline Reser­ vation System has made it possible for Airlines to improve the service they render to their customers. (a) ______~)------(c) ______(d) ______8. List four ways in which the efficiency of the Airline has been improved through the use of the system. (a) ______~)------(c) ______(d) ______(b) Repeat as above, except that the terminals 9. Can Agents sets communicate with each connected to DPC-B all communicate among other directly, i. e. without intervention by DPC? themselves without assistance of the DPC. Show only the portion of the network that must 10. Which governmental agencies regulate com­ be reconfigured. munications?

11. Define Teleprocessing, as you understand it.

IBM CONFIDENTIAL 15

SESSION 3

DATA TRANSMISSION

This session presents the functions of data transmission and control through analogies to normal data processing methods.

Highlights

o Keypunch and Summary Punch as examples of data transmission. o Data Flow in a typical Teleprocessing environment. o Serial versus Parallel transmission. • Interface defined. • Input/Output media available. • Message component sequence, including control signals.

The objective of Teleprocessing is the efficient, to communicate. The summary punch starts to run accurate, and economical transmission of data from if all operational requirements are met, and it sends one place to another. Teleprocessing requires a timed series of pulses to query the accounting originating and terminating equipment, a communi­ machine. The contents of the selected counters and cations facility, and equipment to convert data into storage units are transferred to the summary punch a form that may be handled by the communications and punched into the summary cards. The summary channel. punch then returns an acknowledment signal, in this The simplest form of data transmission, familiar case the "summary punch end" shot to the accounting to most customer engineers, is the keyboard of an machine. Again, the accounting machine reverts to IBM keypunch. This device translates the mechani­ processing data to make another record available to cal keystroke of the operator into electrically coded the summary punch. During processing time, the impulses to punch the required pattern into an IBM summary punch is idle. The initial call of the card. Through mechanical means, the depression accounting machine to the summary punch could be of the key is converted into closures of certain con­ called an inquiry; and it is a turn-around command. tacts in the keyboard. These contacts provide elec­ This means that the accounting machine will not take trical signals to be transmitted over the cable con­ any further action until given permission to do so by necting the keyboard to the remainder of the machine. the return signal from the summary punch at sum­ Control signals are also sent to tell the punch drive mary punch end time. The signal from the summary when all of the information has been transmitted to punch at summary punch end time is a turn-around the punch unit, and to perform the mechanical action command from the summary punch to the accounting of punching the code into the card. A return acknowl­ machine, and the accounting machine again begins edgment signal unlocks the keyboard and permits the processing. This same concept is used throughout next character to be keyed in. This is a form of the field of data transmission and the terms most asynchronous transmission as it requires a stop and frequently encountered have been introduced here. a start signal to control the beginning and end of In order to convert this operation to a true Tele­ each character handled. processing operation, we might hook the previously Another form of data transmission is summary discuss~d summary punch to the accounting machine punching. In this case, the carrier facility or by a mile-long cable. This wouldn't be very practi­ channel is the summary punch cable connecting the cal for several reasons. The most important reason accounting machine to the summary punch. The is that a cable a mile long has considerable resist­ accounting machine sends a signal at "total time" to ance and the si.gnal to the punch magnets would decay the summary punch to inform the punch that it wishes or deteriorate in quality sufficiently to cause a failure

IBM CONFIDENTIA L 17 to punch. This operation could be carried out if the receiving station, a similar interface with a demod­ square wave impulses were converted to alternating ulator and a terminal reconverts the signal to a form current impulses before they were sent; then ampli­ acceptable to the data processing equipment. fied back to their original levels upon receipt by the Figure 7 illustrates a data transmission system summary punch; finally, converted back to DC to and one method of signal conversion used in a tele­ energize the interposer magnets. This conversion phone circuit. The components used are:. process is modulation; it will be used extensively in 1. Input equipment, and IBM 1401 System Teleprocessing, and covered in more detail later in 2. The terminal - an IBM 1009 Data Transmission the course. Unit. In order to use existing telephone and telegraph 3. The modulator - a common carrier company networks for data transmission, data processing data set equipment must prepare suitable input for network 4. Circuit or channel - a communiqations line terminals, or be connected to the network. In addition, 5. Demodulator - a common carrier company data processing codes and signals must be converted data set to signals acceptable to the circuits or channels used. 6. Terminal - an IBM 1009 Data Transmission The data flow shown in Figure 7 starts with input Unit media such as punched cards, a keyboard, punched 7. Output equipment - an IBM 1401 System. paper tape, or magnetic tape. Information enters the system through an input device such as a card Note that the IBM 1009 is both a receiver and a reader; then goes to a terminal and data set before transmitter, capable also of code conversion. Each actually entering the communications channel. The character sent from one 1401 to another over this point at which the data processing and communica­ network is changed in mode from a parallel bit con­ tions equipment connect is called the interface. The figuration to serial form and changed back at the terminal changes the data to a form acceptable to receiving terminal. the modulator. The change or conversion may re­ We have just introduced two new terms "Serial" quire changes in mode, format, speed, code struc­ and "Parallel". When we punch a card from a key­ ture, insertion or deletion of special control char­ punch keyboard, the zone and numeric punches of acters. The modulator converts the signals to the the character are all punched simultaneously into the form acceptable by the circuit or channel. At the card. This constitutes a parallel transfer; that is,

Data Serial by Character, Parallel by Bit Serial by Character, Serial by Bit Processing 1009 System BCD 4/8 Fixed Count Code

Seri 01 by Character, Seri 01 by Bit ------; • 4/8 Fixed Count Code

Bit Serial b Character, Parallel b Bit Data 1009 Processing 4/8 Fixed Count Code BCD System

FIGURE 7. DATA TRANSMISSION SYSTEM

18 IBM CONFIDENTIAL all of the bits or pieces malting up a character are character from 4 of 8 fixed-count code back to binary­ handled at one time. However, when we summary coded decimal, which is the operating code of the punch a card using, for example, a 407 and a 514, data processing system. we punch the digits in the card in the order of 12 In Figure 7, we have considered the data proc­ punches, 11 punches, 0 punches, etc., down through essing system to be a 1401. This data processing the 9 numeric punch. If we punch just one column of system could actually be anything from a data trans­ the card on a summary punching operation, we are ceiver to a full System/360 operational complex. serially punching the character into the card; that is, Some of the available input/output choices are: cards, if the character represented is an A, we punch first magnetic tape, punched tape, printed copy, visual the 12 punch, skip the 11, skip the 0, another punch display in lights or visual display of characters on at 1 time, and skip the remaining punching positions a television-type tube. In addition, data being han­ 2 through 9. Thus, scanning a storage unit in the dled could come from a disk or drum file of one 407 accounting machine where the letter A was computer system to the main memory of another stored, we have converted the character from its system. parallel format in the storage unit to one bit at a The connection of the data processing system to time transmission over the summary punch cable to the communication equipment is called the "Inter­ the 514. face". In the case of data transmission, the inter­ Another application of data handling is the mag­ face or demarcation strip provides a dividing line netic tape unit in which characters are written one between the responsibility of IBM and that of the at a time, in parallel format, across the width of the communication company. For this reason, each magnetic tape. In this application, we have parallel manufacturer or supplier of communications equip­ characters recorded serially; that is, one full char­ ment for attachment to business machines provides acter at a time. The manner in which we transfer a publication called "Interface Specifications". data to a tape drive is referred to as "serial-by­ This publication defines what signals the business character, parallel-by-bit". The data processing machine must provide for the communications equip­ system in Figure 7 transfers information to the 1009 ment and describes the nature of signals which the by this method. In the 1009, the characters received communications equipment will return to the business from the data processing system in binary coded machine. decimal are converted to a fixed count 4 of 8 code. In Figure 7, the interfaces that exist are from For comparison of BCD with 4 of 8 codes, see Fig­ the data proceSSing system to 1009, from the 1009 ure 7. In addition to converting the code, the 1009 to the data set. On the receiving end, from the data takes each character, after it has been converted to set to a 1009, and from the 1009 back to the data 4 of 8 code, and instead of transmitting that charac­ processing system. ter in one swat over the communication line, it trans­ Besides handling data ("text" of the transmission), mits the character one bit at a time (like the A from this type of system sends and receives coordinating 407 to 514). The data is still in a form unacceptable signals. The most common of these are listed in the to the communications facility. Thus, we require the sequence of their normal use: service of the data set between the communications 1. Inquiry The transmitting end checks the line and the 1009. receiving end to see if it is ready The data set will perform an interface conversion to receive. function of changing the fixed-count 4 of 8 code bits 2. Turn-around Both ends switch their sending from the 1009, which are still in DC pulses, into a and receiving functions. (Time form that the line facility will accept. The data set required may be up to 200 milli­ is modulating the line signal in accordance with data seconds. ) being presented by the 1009. The data appears on 3. Acknowledge By this control signal, the receiv- the line in serial by character, serial by bit format ing end becomes a transmitter in 4 of 8 fixed-count code. As it is received by the and signals the transmitting end J data set at the receiving end, it will be received to proceed. serial-by-bit, serial-by-character and delivered in 4. Turn -around is repeated. 4 of 8 fixed-count code to the 1009 in DC pulses. 5. Start of Sending end begins transmission The 1009 will accumulate these bits one at a time Record with proper heading control, until it has a full character, and then transfer the followed by full text of that record. characters one at a time to the data processing 6. End of Trans- This control signal follows the system. A conversion from serial-by-bit, serial­ mission or last character of the record. It by-character, to parallel-by-bit, serial-by-charac­ End of usually includes an LRC (Longi­ ter has been effected. We have also translated the Message tudinal Redundancy Check)

IBM CONFIDENTlA L 19 auuurnulaLiuIl uf Lhe LexL irnrneui­ 8. TUl'n-arUWld is again repeated and sequence ately preceding. continues from 5. An LRC is essentially an odd/ In handling data flow on this communication network, even count of the bits transmitted we spoke of parallel-by-bit, serial-by-character in the preceding message. It processing which was then converted to serial-by­ constitutes a turn-around command bit, serial-by-character. The process of convert­ and causes the sending end to a­ ing data from parallel-by-bit to serial-by-bit is also wait reply from the receiving end. called "serialization". The reverse process on 7. Acknowledge is repeated if the message has receiving (i. e., receiving one bit at a time and con­ been received without error and verting it into a full character) is called "Deserial­ the LRC agrees with that which ization". Having covered the requirements of the the receiving end has accumulated. terminal equipment, we turn to the communications (Some acknowledgment signals channel. permit the sending end to ascer­ This completes the text for Session 3. If you can tain whether the message was answer all of the following review questions correctly, successfully received or whether you may go to Session 4. If you answer any questions it should be repeated.) incorrecey, review the appropriate sections of the text before proceeding.

20 IBM CONFIDENTIAL R:EVIEW QUESTIONS 10. List 6 choices of input and output media available for this operation. (a) ______1. When a character is transferred from the KeypWlch keyboard to the punching Wlit (serial/par­ (b) ______allel) mode transmission is employed. (Underline (c) ______choice. ) (d) ______2. Summary punching is an example of (serial/ (e) ______parallel) transmission. (Underline choice.) (~------3. Briefly describe what is meant by a "turn­ 11. The function of an interface or demarcation strip is: ______aroWld command".

12. To what would you refer if you wanted com­ plete information regarding signals exchanged be­ 4. What is modulation, and why is it used? tween a data terminal and a common carrier data set? ______

13. Converting data from serial-by-character, parallel-by-bit to serial-by-character, serial-by- bit is called ______14. The process of receiving characters serial­ by-bit and then transferring them in parallel-by-bit 5. Data transfer from the IBM 1401 in the text form is called ______figure to the IBM 1009 is in serial-by-character. 15. Why is an LRC exchanged between the sending ______bilform. and receiving terminal? 6. Data transfer from the IBM 1009 to the Data 16. What control signal usually indicates the be- Set is in serial-by-character, ______ginning of the Text portion of a message? _____ bit. 7. The signal on the line is ______17. What control signal is sent by the transmitting by the data stream from the IBM 1009 to the Data terminal to the receiving terminal to check whether Set (when transmitting). or not it is ready to receive? ______8. On the receiving end, the Data Set ______the line signal and provides _____ 18. What reply is expected by the transmitting ______bit, serial-by-character input to the terminal of question 17 ? ______IBM 1009. 9. Between the receiving IBM 1009 and the IBM 19. List 3 control signals which are considered 1401, the received characters are transferred as turn-around commands. serially in bit form and, at (a) ______the same time, are translated from (b) ______code to code. (c)______

IBM CONFIDENTIAL 21

SESSION 4

COMMUNICATIONS CHANNELS

This section covers the kinds of Communication facilities available for data com­ munication, the equipment necessary to provide these services, and their combined characteristics and problems.

Highlights

• Types of channels Simplex Half-Duplex Full-Duplex • Signaling Methods Morse Code Baudot Code Binary Coded Decimal (BCD) 4 of 8 Fixed Count Code American Standard Code for Information Interchange (ASCII) ., Frequency Spectrum, Carrier Systems and Channelization o Types of Modulation Amplitude Modulation Frequency Modulation Phase Modulation o Grades of Channels Broad Band Voice Grade Subvoice Grade Telegraph Grade • Line Quality Attenuation Phase Delay and Distortion Crosstalk Repeaters Echo Suppressors, Turn-Around, Conditioning, Compensators, Loading Coils Measurement of Decibel Levels o Data Set as an interface device

IBM CONFIDENTIAL 23 Table 1. BCD and 4 of 8 Code

.. BCD BCD 4 OF 8 TR CODE (ODD PARITY) 4 OF 8 TR CODE (ODD PARITY) Symbol Symbol 1 2 4 8 R 0 X N 1 2 4 8 C A B 1 2 4 8 R 0 X N 1 2 4 8 C A B

Space 2 4 8 0 A W 2 4 0 N 2 4 A 0 2 8 R N 2 8 C X 1 2 4 0 1 2 4 C A 1 1 0 X N 1 Y 8 R 0 N 8 C A 2 2 0 X N 2 Z 1 8 0 N 1 8 A 3 1 2 R N 1 2 C / 1 l\ 0 N 1 C A 4 4 0 X N 4 #= 1 2 8 R 1 2 8 1 2 8 N 1 2 8 A B 5 1 4 R N 1 4 C 6 2 4 R N 2 4 C $ 1 2 8 X 1 2 8 C B 7 1 2 4 R 1 2 4 , 1 2 8 0 1 2 8 C A (W' 4 8 R N 4 8 C 8 8 0 X N 8 9 1 8 R N 1 8 C o ) 4 8 0 X 4 8 C A B A 1 R 0 X 1 A B * 4 8 X N 4 8 B 4 8 0 N 4 8 A B 2 R 0 X 2 A B %( C 1 2 0 X 1 2 C A B &+ 2 4 8 N C A B D 4 R 0 X 4 A B - 2 4 8 X B E 1 4 0 X 1 4 C A B 7 2 8 0 X 2 8 C A B F 2 4 0 X 2 4 C A B ! 2 8 X N 2 8 B G 1 2 4 N 1 2 4 A B RM:f 2 8 0 N 2 8 A GM$ 1 4 8 N 1 2 4 8 C A B H 8 R 0 X 8 A B I 1 8 0 X 1 8 C A B MCiJ. 1 4 8 X 1 2 4 8 B J 1 R X N 1 C B SM -tt+- 1 4 8 0 1 2 4 8 A WS-V- 2 8 R X 1 4 8 C A K 2 R X N 2 C B TM";- 1 4 8 R 1 2 4 8 C L 1 2 X N 1 2 B M 4 R X N 4 C B > 2 4 8 R 2 4 8 < 2 4 R 0 2 4 8 A B N 1 4 X N 1 4 B 0 2 4 X N 2 4 B j 4 8 R 0 2 4 8 C B P 1 2 4 X 1 2 4 C B \ 2 8 R 0 2 4 8 C A : (Note 1) .. 1 2 4 8 1 4 8 Q 8 R X N 8 C B R 1 8 X N 1 8 B [ 2 4 R X 1 4 8 A B S 2 R 0 N 2 C A ] 4 8 R X 1 4 8 C B T 1 2 0 N 1 2 A Blank (Note 2) R 0 X N C U 4 R 0 N 4 C A V 1 4 0 N 1 4 A

NOTES: 1. This character is transmitted as the substitute character 2. An :lll-..ero 7-bit character is illegal, even when the tape unit is operating in even parity, because an attempt to write it on tape causes a tape echo check.

24 IBM CONFIDENTIAL A channel, circuit, or line is a path for electri­ requires a certain amount of turn-around time. In cal transmission between two or more terminals. most applications, this is in the vicinity of 200 milli­ The channel may be a group of wires or a special seconds. In preliminary planning for a network, part of the radio frequency spectrum. The channel consideration must be given to the time required for carries information from one place to another. Al­ answer-back signals that can occur before, during, though "circuit" is used conversationally as a syno­ and after each message as a response from there­ nym for channel or line, technically, a circuit can ceiving station, indicating a ready-to-receive status. contain several communications channels. In some instances, the time required for the answer­ back can affect the throughput of a data transmission TYPES OF CHANNELS system. The three basic channel types are Simplex, Half­ The terms Simplex, Half-Duplex and Full-Duplex Duplex, and Full-Duplex. (See Figure 8.) represent the types of circuits. The names indicate A Simplex circuit can carry information in only only the directional c~pabi1ity of the channel or cir­ one direction. It is Simplex because, in most cases, cuit. The grades of channels, however, are Broad the type of sending or receiving units cause this Band, Voice Grade, Sub-Voice Grade, and Tele­ restriction. graph. Circuits are graded on their basic line speed A Half-Duplex circuit can carry information in (transmission rate) expressed in characters per either direction but only in one direction at a time. second, bits per second or words per minute. Since A Duplex circuit or Full-Duplex circuit can carry these different grades of circuits use different types information in both directions at the same time. of signaling, an understanding of code structures is A network can consist of any combination of these, necessary to evaluate their potential. The following according to the application requirements. In a half­ section introduces some of the more common codes duplex telephone circuit, reversing the flow of data and signaling techniques now in use.

1SwH,h Battery II II ',rr0 Simplex Circuit (SPX)

• A

Battery S~. II I' Half Duplex Circuit (HDX) swr 0 Battery I II I I II I ~sw Battery Full Duplex Circuit L9

FIGURE 8. CIRCUIT TYPES

IBM CONFIDENTIAL 25 SIGNALING METHODS Character Sent Line Signals Perforated Tape

Morse or international code is made up of dots and dashes. For example, IBM, in Morse code, is two dots, a pause, a dash, and three dots, pause, two Impulses a. 1 2 3 4 5 dashes. Although this code is written as dots and ~12345Ji dashes, the actual transmission consists of long and short signals with pauses between characters. The ••• use of long and short intervals, intermixed with • •• pauses, indicates that time is an element of trans­ •••• mission. Compare the transmission of the code for • • V, (see Figure 9) that is, three dots and a dash, • with the actual periods of signal. The presence or • ••• absence of a signal indicates the character configur­ •••• ation. This code was developed for manual telegraph ••• 0·0 signaling, and the experienced operator could differ­ •••• entiate between letters because of the length of the ••••• no-signal or pause condition. Early mechanized •• • telegraph equipment could not handle Morse code •••• because the characters varied in length between ••• pauses. A five-bit code (called the Baudot code, for 8. its inventor) was developed and is still used (see , ••• Iii Figure 10). •••• • The most common form of the Baudot code in • • • telegraphic use requires 7.42 bits or units of time --- • • • per character. Only five of these units are used to - - - • carry information. A bit, in this instance, is the •••• fixed unit of time in which a signal is present or ••••• absent. One bit is used as a start signal and 1. 42 ••• • bits as a stop signal (replacing the pause used be­ • •••• • • • • tween letters in the Morse code). The stop signal ------shown in this example is 1. 42 bit times. The pres­ • • ence of a bit or signal on the line is a: Mark; the - •• - • • absence of a bit or signal is a Space. Baudot code - signals consists of Marks and Spaces. The start bit, - • -- ••• •• corresponding to the pause between characters in •••••• Morse code, is always a space. The long stop bit is always a mark and the line is in a mark condition - when not being used. Thus, the start and stop bits D Spacing Impulses of the character perform also the functions of syn­ • Marking Impulses chronizing the equipment at both ends of the commun­ ication facility.

VI VI VI 0::: (!) 0::: !:iAB U:9124 !:iADA,MS 3.GGGG•••••••••...... GO•• 0000 •• 0. 4 • ••• • ••• 5 ~.___ ._. __ ._. __ • __ •______• __~ Pause Dot Dot Dot Dash Pause

FIGURE 10. BAUDOT CODE

Code • • • Signal:

No Signal:

FIGURE 9. MORSE CODE TRANSMISSION OF LETTER "V"

26 IBM CONFIDENTIA L The following anecdote describes the origin of the Early electromechanical telegraph sending units, terms "mark" and "space". At each end of the circuit used to transmit Baudot code, were attached to a on the old Morse code telegraph, there was a tele­ three-row keyboard resembling that of a typewriter. graph key to switch the line current OFF and ON, Five contacts (one for each bit in the code) were and an associated electromagnetic type "sounder". arranged in a circle. Each time a key was depressed, (See Figure 11.) When the line was in the idle state, certain of the five contacts were activated, tested by full current flowed and the electromagnetic sounder a rotary wiper arm, and then reset. Figure 12, armature was attracted to the pole piece. Copying titled Transmission Modes, shows this mode of the message consisted of listening to the spacing between clicks of the armature striking the pole piece of the sounder. A short gap between clicks was a dot and a long gap between clicks was a dash. According to the story, the telegraph operator wanted to sneak out for a cup of coffee without missing any #1 Sounder #2 Sounder of the transmission coming to him. He attached a pencil to the armature of the sounder and then rigged up a reel of paper strips pasted together to form a ~ long piece of narr.ow tape. He ran the paper past the pencil and wound it up on another reel under con­ trol of an old clock works. The result was that, so long as the current flowed in the line, the pencil marked on the paper tape; whenever the line was line opened by keying, the pencil moved away from the - Loop T Battery paper tape and the tape merely spaced. Therefore, the line was either marking or spacing. The terms have remained to the present day. FIGURE 11. SIMPLE TELEGRAPH CIRCUIT

Units of Time

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Serial Start - Stop

a. Cl. Cl. 0 0 0 0 C .E ClIlI Iii.ii:t:I Vi Vi m::IiI CIIIII &113 Vi Vi I!!IIIII CI:Cl Vi VI .. III A ~ III ~ ... C .. Serial Synchronous .. -.. - A ~ .. --~ -4 --C - ~

Parallel - Second Channel - Third Channel ED - Fourth Channe I ~ - Fifth Channel A -C

WiOiiiI = Mark or Current Flowing in Telegraph line

FIGURE 12. TRANSMISSION MODES

IBM CONFIDENTIAL 27 transmission under a classification mown as Serial I I I I I Start-Stop (also called asynchronous). For example, Amplitude r----- h Y\ H 1 the letter A, when depressed, activated only the I \JI~ U first and second contacts of the five. As the rotary I I I I 1 wiper started testing the five contacts, it sent an I- One -I I 1 I Cycle I I I automatic no signal or space indicating the start of the character, then marks from the first two con­ tacts, spaces from the remaining three, and finally, FIGURE 13. AC SINE WAVE a long mark for the end of character or stop signal. Conceivably, if the sending and receiving term.inals were controlled by the same timing pulse, the start and stop bits could be eliminated. Characters would be detected on the basis of every five bit times. The serial start-stop Baudot code requires 7.42 units of The extend of the oscillation represents the rel­ time for each character of 7.42 bits. Without start ative energy level and is called the Amplitude; each and stop bits, however, the character requires only complete oscillation is called a cycle. Thus, the five units of time for the five actual intelligence bits. figure indicates three complete cycles. The number Transmission without start and stop signals is termed of times that one of these cycles occurs per second Synchronous. is referred to as the frequency of the wave. Fre­ In synchronous signaling, a special pattern of quency is usually expressed in cycles, kilocycles, bits is sent periodically to keep the terminals oper­ or megacycles (abbreviated CPS, KC, MC). A ating in unison. In most IBM applications, these are newly adopted term called Herzians (Hz) corres­ called idle characters. They are generated auto­ ponds to cycles. The overall frequency spectrum matically and sent as required by the system. for electrical communication ranges well above In addition to the serial start-stop and synchro­ 30,000 megacycles. Different parts of the frequency nous methods of transmission, the figure also shows spectrum are used for various types of communica­ how the same characters can be sent over five chan­ tion because the characteristics and behavior of the nels simultaneoulsy, allowing one channel for each signals change with the frequency. bit in the code structure. This is called Parallel Transmission. It is much the same as the keyboard CARRIER SYSTEMS of the key punch transmitting data to the punching unit. The lower costs of communications today have been In summary, a network may include Simplex, made possible by the efforts of communications Half-Duplex, or Duplex channels. The transmission engineers in using the frequency spectrum to full mode may be Serial Asynchronous, Serial Synchro­ advantage by employing Carrier Systems. These nous, or Parallel. In addition, depending on the systems carry many conversations or messages on rate of transmittion necessary, it may require a a single circuit. The human voice has a frequency Broad Band, Voice Grade, Sub-voice Grade, or range of approximately 50 to 16,000 cycles per Telegraph Grade channel. second. If modern telephone systems were allowed to use this entire frequency range for each conver­ FREQUENCY SPECTRUM sation, only very few conversations per channel would be possible at anyone time; and the cost per The basic method of transmission in telegraphy is the call would be high. Communications engineers have use of the key, a switch or a rotor to interrupt per­ found that a frequency range or band approximately iodically the flow of direct current (dc). Various~ three kilocycles wide is sufficient to retain most of other methods have been developed which are more the individual characteristics of the human voice suitable for transmission over long distances. Fig­ during transmis sion. Since many telephone circuits ure 13 is the schematic representation of an electro­ have a range or bandwidth of 150 kilocycles, at 3 kcs magnetic wave. Radio waves (which are electro­ per channel we can have 50 possible voice channels magnetic waves), electromagnetic waves in a wire in this range. The problem, of course, was to de­ conductor, and sound waves share the common char­ vice a method of carrying voice signals at different acteristic of oscillating perpendicular to the direc­ frequencies on the same line. Through a method tion of movement of the wave. In the figure, the mown as multiplexing, each three kilocycle band is perpendicular oscillation is shown to have occurred assigned an individual sub-carrier frequency to be three times. transmitted by the carrier facility. Thus, in much

28 IBM CONFIDENTIAL the same way that we can send many radio frequency To allow buffering, we have also provided to this carriers through the air at one time, we can send same channel the spectrum up to 19 kilocycles to multiple carriers over a wire at one time. The only prevent interference from one channel to another. restriction is that the frequencies used must endure The modulators and demodulators, along with the transmission without excessive loss. On the trans­ fixed carrier frequencies, act to raise and lower the mitting end of the carrier facility, modulators are voice frequency level. By using different oscillators, necessary for each of the sub-carriers used. On generating different carrier frequencies, the same the receiving end, demodulator circuits are neces­ technique can be used for bands A, C, and D in Fig­ sary to extract the original messages. (See Figure ure 15 to provide four simplex voice channels on a 14. ) single wire. Band B shows the upper side band of three kilocycles as previously described. In a more MODULATION complex carrier system, more channels can be provided. Consider an imaginary one-wire communication The three-kilocycle band, used in the preceding channel capable of carrying frequencies from 10,000 illustration, can be further subdivided into bands of to 30,000 cps. The human voice with a range of 50 150 to 200 cycles each. These are not wide enough to 16,000 cps is used to control the flow of current for the human voice but could be used for the trans­ in a telephone hand-set. Filtering circuits within mission of information in code. For data transmis­ the telephone hand-set permit only frequencies from sion, a code structure based on the presence or 200 to 3, 000 cps to pass. This signal enters the absence of a bit or Signal can be indicated by changes modulator and controls the operation of an oscillator. in the waveform of the side band frequency trans­ The oscillator's frequency is permitted to vary in mitted. Figure 16 illustrates some modulation proportion to the frequency of the applied signal. methods and shows the relationship between the Thus, if the oscillator'S center frequency is 15,000 binary-coded data, the presence or absence of a cps, we have 15,000 cycles plus 200'to 3,000 cycles, signal, and the representations of the various wave­ and 15,000 cps minus 200 to 3,000 cycles. We ob­ forms produced for serial transmission. The binary­ tain an upper side band from 15,000 to 18,000 cycles, coded data is indicated by a 1 or a 0 corresponding and a lower side band from 15,000 'cycles down to to the bit configuration. Thus, the presence of a 12,000 cycles. The upper and lower side bands both bit is aI, the absence of a bit is a 0, corresponding contain the same waveform or signal and either can also to a Mark or a Space respectively. The exam­ be used for the actual transmission. ple of Amplitude Modulation indicates a drop in the At this point, filters are used to eliminate or amplitude for a no-bit conditiqn. Frequency Modu­ suppress the carrier and, in this example, the lower lation changes the frequency of the carrier to indi­ side band. The upper side band alone with a frequency cate a no bit. Phase Modulation is not limited to the of 15,000 to 18,000 cps (which is a direct function of illustrated 1800 change but may be accomplished by 0 .the original voice signal) is routed to the telephone a 90 or other change according to the design of the wires or cables. At the receiving terminal, the terminals and the quality of the channel. For Phase 0 voice signal enters the demodulator and filter. The Modulation, the IBM 3977 Modem utilizes a 180 recovered voice signals, reduced from 15,000 - change. Various common carrier data sets employ 18,000 cps to the audible level of 200 - 3,000 cps, four-phase Modulation using shift increments of 450 • are forwarded to the receiving telephone hand-set.

30 kc

Band D 25 - 29 kc

~ :0 Band C 20 - 24 kc 0 Band D u 25 - 29 kc !(; Band C Band B 15-19kc ~ 20 - 24 kc /I,.qI'j,,'V-A,<-, U-'p-'-pe_r_Si_de_b_an_d __15_-_1_8_k_c_. 15 - 18 kc ~ EJ Band B Band A 10 - 14 kc Modulator '(.... tlt', Carrier Signal 15 kc ~ Filter - 15 - 19 kc Band A -\ 'v.,ft., Lower Sideband 12 - 15 kc 10-14 kc

FIGURE 14. MODULATION AND FILTERING, CHANNELIZING FIGURE 15. EXAMPLE OF CARRIER CHANNELS (CHANNELIZATION)

IBM CONFIDENTIAL 29 Binary Coded Data: o requires a band width of about 4,000 cycles. On the Signal: carrier system that we looked at previously, this

No Signal: would eliminate our buffer channel to prevent inter­ ference. Technological advances have made it pos­ sible to pass 2, 000 bits per second over a three Carrier: kilocycle band width. The number of bits per second over a given band width of channel is a function of the type of modulation used. Amplitude The grades of channels we will look at are Broad Modulation: Band, Voice, Sub-Voice, and Telegraph. This is in' descending order of bit handling capacity. These grades do not imply strict limitations. There are Frequency Shift general categories of high, medium, and low speed Modulation: facilities that are specifically described in tariffs filed with the Federal Communications Commission or equivalent State utility Commissions. Phase Modulation: Broad Band Channels

Broad band channels, via microwave or radio relay 1 800 1800 180 0 Change Change Change communications systems, use the super-high fre­ quencies above 3,000 megacycles. Radio waves of these frequencies tend to travel in a straight line FIGURE 16. MODULATION TYPES requiring repeater stations with dish -like antennae on high buildings or towers every 20 to 35 miles. Carrier, modulation, and channelizing techniques GRADES OF CHANNELS are used. The speed of transmission is limited only by the band width available. Some idea of the cost The agreement between the communications common of a broad band channel can be gained by noting that carrier and the subscribers is basically an arrange­ one type of channel capable of carrying 5100 char­ ment for the use of a certain type and grade of com­ acters (40. 8k bits) per second costs about $15 per munications channel. The channels are classified mile per month. This is similar to the common by type, i. e., Half-Duplex or Full-Duplex, and by carrier Telepak service. The IBM 7710 or 7711 grade, i. e., the capacity of the channel to carry Data Communication Unit provides point-to-point information in bits per second (or a similar grading communication over a Broad Band channel at speeds factor). The physical circuit or technique used, up to 230,400 bits per second (28,800 characters whether a voice frequency circuit, a wire carrier per second). If the customer's application cannot channel, or a portion of a microwave band, depends justify the utilization of Broad Band channels, the on the facilities available in each geographic loca­ same equipment can be operated over a Voice Grade tion. The subscriber is not necessarily concerned channel at lower rates. The 7710 and 7711 are com­ with the fact that a voice grade channel uses a car­ patible with the 1009 Data Transmission Unit, the rier frequency of 15 kilocycles or 500 kilocycles but 1013 Card Transmission Terminal and the 7702 only that the available band width is capable of carry­ Magnetic Tape Transmission Terminal. ing the required volume of information with the spec­ ified degree of accuracy. Voice Grade Channels The line speed of a channel, measured in bits per second, is direotly related to the band width of the Voice grade channels have a band width of approxi­ channel. It is important to keep this in mind be­ mately three kc and, when used for voice communi­ cause a high bit rate per second requires a wider cation, can carry only one conversation. In data channel (more cycles per second). Anything occur­ communications, it is possible to handle 2,400 bits ring in the channel which would tend to limit the per second with this type of a line facility. Higher transmission band width of that channel will, of nec­ speeds are possible but are dependent on the com­ essity, limit its transmission rate also. The com­ mercial availability of suitable channels and termi­ munications companies have found that from a prac­ nal equipment. The common carrier can channelize tical point of view, considering cost and performance, the voice grade line into smaller bands (of 150 to the band width should be about twice as wide as the 200 cycles) each suitable for Subvoice or Telegraph number of bits per second passing through the chan­ communications: that is, for up to 200 (approxi­ nel. This means that to handle 2, 000 bits per second mately) bits per second of transmission. The co:::t

30 IBM CONFIDENTIAL of a leased Voice Grade line used for data is de­ Telegraph Grade Channels termined by the length and type of channel. Dialed calls for data transmission are usually charged at The line speeds of these circuits range approxi­ the same rate as ordinary voice telephone calls. A mately from 45 to 75 bits per second. The circuits telephone and data set are required at each terminal. normally employ asynchronous mode of transmission; A telephone connection is established between two that is, both start and stop bits are required to syn­ terminals either by direct dialing or through an chronize the two ends of the operation. The telegraph operator. Each terminal attendant then presses a was the first effective means of cross-country elec­ data key on his phone to connect the data set to the trical communications. One of the characteristics of line, and disconnect the telephone. Pressing the early telegraph lines was the use of regenerative key establishes a direct line for data transmission repeater stations along the circuit. As mentioned between the two terminals and prevents use of the before, the quality of the DC signal decays on a nor­ telephone. The completion of this operation is called mal line as we go along that line, due to resistance Channel Establishment. Sometimes it is referred to and other characteristics of the line. as the "hand-shake routine" or other similar termi­ To maintain the quality of communication, me­ nology. The IBM equipment, encountered on this chanical repeaters were necessary to regenerate a type of channel, may range from a 1001 to a complete distorted or a decayed signal (one whose quality was System/360 utilizing IBM 2701 or IBM 2702 through no longer satisfactory for operating a teleprinter) data sets to the line. into a good, clean signal. This repeater samples the weak, distorted signals and then generates a ~ubvoice Grade Channel s completely new, undistorted signal to forward along the line. Regenerative repeaters, however, are Subvoice grade channels have a lower speed than code-sensitive and may restrict transmission to the Voice Grade channels. There are no specific limits code for which the repeater was designed. but Subvoice grade channels are usually considered Some electronic type repeaters have recently to be those below 600 bits per second transmission been introduced which are not code sensitive. The rate. The following are examples of utilizing Sub­ IBM 65 and 66 Data Transceivers are units used in voice Grade channels. conjunction with IBM 067 Signal Unit to send and receive punched card data over telegraph grade cir­ IBM 1030 Data Collection System - An Application cuits, at 60, 75, and 100 words per minute to pro­ vide the capability of sending approximately 3, 4, or The IBM 1030 has a transmission rate of 60 charac­ 5 cards per minute. ters per second. The 1030 is a multi-application data collection system that provides two-way com­ LINE QUALITY munications between a centralized IBM 1440 or 1460 Data Processing System and remote locations in a In discussing line quality, some of the terms that we plant utilizing an IBM 1448 Transmission Control encounter are: resistance, impedance, conductance, Unit. With the appropriate adapter, this system can and attenuation. In this introductory course, how­ be linked to a 1410, 7010, or a fully complemented ever, only a few of the communications problems System/360 through a 2701 or 2702. will be covered to illustrate techniques used to pro­ The IBM 1050 Data Communications System is vide faster and more accurate communications. the general purpose data terminal for on-line trans­ Based on theory, electrical communications mission or off-line preparation of data at rates up to travel at the speed of light. In practice, however, 14.8 characters per second. Input and Output de­ wires and cables have characteristics that tend to vices include the 1052 Printer-Keyboard, the 1053 reduce this speed. The frequency of transmission Printer, the 1054 Paper Tape Reader, the 1055 Card is a direct factor in determining how effective these Punch; all are controlled through the 1051 Control characteristics are in changing the propagation rate Unit. Each terminal can communicate with another of the signal. Some factors that influence the effi­ 1050 system, an IBM 1440, 1401, 1410, 1460, 7010, ciency of long distance wires and cables are: the or to the 2701 or 2702 of a System/360 installation. distance involved, the ability of copper or aluminum The IBM 1060 Data Communications System is wire to carry the signal, interference from other designed for banking applications. The IBM 1070 circuits (crosstalk), and electrical characteristics system is designed for process control applications. which cause distortion or loss of signal. Either system may be connected also to System/360 Before tubes and amplifier circuits were devel­ through the 2701 or 2702 with the appropriate adapter oped, the length of a telephone line was limited to units. relatively short distances. Amplifiers increased

IBM CONFIDENTIAL 31 the signal strength and the useful length of a line but The common carrier personnel talk about power required additional feedback in the amplifiers (for levels and signal levels on telephone lines in terms this particular application, called repeaters) to of decibels. Your readings, however, using an IBM prevent howling noises. Their function was to build Line Adapter, and injecting a signal on a leased-line up the line signal and prevent loss of signal along facility, will be in peak-to-peak volts from your the telephone line. oscilloscope. A problem in long-distance voice lines is a suc­ The reference, 0 dbm, is equal to 1 milliwatt in cession of echoes of diminishing volume that is dis­ a load of 600 ohms. This would correspond to a turbing to the person speaking. To solve this prob­ voltage level of .775 volts RMS or 2.2 volts peak-to­ lem, an echo suppressor was developed. The echo peak. Figure 17 provides a graph for rapid conver­ suppressor takes effect just after speaking starts, sion of db levels from +10 to -50 db in terms of peak­ and drops out just after speaking stops. The slight to-peak voltage readings that you obtain from your delay is unnoticeable in a conversation and the echo oscilloscope. problem is elimated. The delay required for the In summary, we are interested in attenuation of echo suppressor to drop out is known as "Drop-out a line as measured in a unit called the decibel; we Time" or "Turn-around Time" and must be taken have explained companders, echo suppressors, com­ into consideration when using a Voice Grade line for pensators, and repeaters. Having covered some of data transmission. If a terminal begins to transmit the concepts of types of channels, grades of channels, too soon after receivin~, data bits could be lost. the quality of a particular channel, channelization Devices designed specifically to compress the methods, and the kind of equipment used on lines, volume range of the human voice for economical we know that a telephone line consists of a lot more transmission and to prevent crosstalk and noise are than just two pieces of wire strung across the coun­ called Companders. Compander is a contraction of try, and we are ready to look at data sets. the words "compressor" and "expander". Effectively" soft sounds are amplified to a higher power level, DATA SETS and loud sounds are amplified to a lesser degree. The pr.ocedure is reversed by expansion at the re­ Data sets are mown also as subsets or modems. ceiving end. The common carrier normally removes The word modem is a contraction of modulator-de­ companders from circuits used for data transmission. modulator. Data sets perform the necessary inter­ It is possible for a common carrier to provide face conversion between data processing equipment lines of especially high quality at additional cost. and communications facilities. They are used at These specially conditioned lines permit data trans­ each termination of the communications channel at mission at lower error rates or higher rates of its interface with the data processing equipment. transmission than would otherwise be possible. One The basic function of a data set is modulation and disadvantage of conditioned lines is that alternate demodulation for data transmission. Following is routes may not be readily available should they be an examination of typical data set specifications: required. Usually, loading coils are inserted into 1. .Equipment: - Transmitter Receiver - It is the line at proper intervals. These are inductive not implied that the device is an original input or loads to compensate for the capacity of the line. output device but that it functions both as a modula­ They will, in some cases, cause unwanted distortion tor and demodulator. One is required at each ter­ of the data signals. Loading coils are sometimes -minal in a network. combined with resistance and capacity to correct 2. Transmission: Binary Serial delay or attenuation characteristics of the line. 3. Input-Output: Binary - Conforms to EIA When used in this manner, they are referred to as RS-232-A. This designation indicates that a binary compensators. code representation, meeting the current recom­ The signal levels on telephone lines are measured mended standards of the Electronic Industries Asso­ in a unit called the "decibel", abbreviated db. In ciation, must be used by the data processing equip­ telephone m:> rk, specifically where the line imped­ ment with the appropriate hardware adapter. (For ances are based on 600 ohms, the db changes to dbm availability of documentation on RS-232-A, see ref­ (decibel milliwatt). The ·reference level for this erences at end of session.) measurement is 0 dbm equals 1 milliwatt dissipated 4. Modulation: FM - Frequency modulation is in a load of 600 ohms. The formula for determining used. Frequency modulation in telephone work can . P-out db IS: dbm = 10 Log 10 P-;cl be either straight FM (e. g., frequency shifting) or If we use 0 db as the reference, the reference it can be phase modulation. power is .001 watts, or 1 milliwatt, and we can 5. Bit rate: 150 to 1200 bits per second - The measure relative to other signals either above or bit per second range over which the data set can below this level and obtain + or - db readings. operate.

32 IBM CONFIDENTIAL 3

2

0~-9-+_±;~~·ct~~.H~t~~!_±~~1rb~_±_~~~hH++~~~~~~_++_~_~++~.~~hH'~,j+_~+'_+:_~clH~!H;!~~l+~~.b;C·~,_,HC~_F~-~+~~~ o. 8 i=E =f= . =i • - ::r:-:=:==._ ,. 0.7 --5 0.6

.:: ~0.2 E "0 > ~ ::i 0.1

0.08 0.07 0.06 0.05 0.04

0.03

0.02

O.Ol~~~wu~~wu~~wu~~~~~~~~~~~~~~~~~~~~~ o -10 -20 -30 -40 -50 FIGURE 17. LINE VOLTAGE VS DBM

6. Synchronization: None provided by this type 7. Operation: 2-Wire Half-Duplex - Indicates data set. Synchronization is referred to as the that the data set and channel can carry information "synch" or "clocking". The clock is not a simple in both directions but not simultaneously. mechanical or electromechanical device but an elec­ 8. Unattended Answer: Yes - Indicates that an tronic component that provides a constant pulse rate. inCOming call can be connected without human inter­ The clock is used by the receiver to control the vention. sampling of received data and keep in step with the Additional information given may include power data flow. Some high-speed data sets (above 1200 requirements. bits per second) utilize either internal or external Certain basic lines are necessary to control the clocking. operation of a data set with a data terminal. (See Figure 18).

IBM CONFIDENTIAL 33 the Send Data line, the Request to Send, and simi­ ~arly what the data set will deliver on the Clear to Send line and the Received Data line. x * Rev Data De - Mod IJ From line 2. Some data sets are equipped with automatic gain control (A GC), while others are equipped with Carr Det only manual gain control, which requires setting by SCR the common carrier personnel for the levels of sig­

DCT nals encountered on the communications line. 3. It is important that the customer engineer SCT understands whose responsibility each of these lines * Snd Data is, the line characteristics, and the permissible variations from established criteria in the interface X * Req Snd - Mod IJ To Line specifications. * Clr Snd Reference Sources Intlk A self-study course, consisting of an audio tape and Fr Gnd work books, is offered on the basic STR Synchronous ~ Transmitter-Receiver. Your field manager may * = Basic Lin es consult the Field Education Guide to determine or­ dering procedures for this course.

FIGURE 18. BASIC DATA SET A special self-study course is also available for the UC STR (the Universal Code STR) which is attachable to a multitude of processors. Your field manager may refer to the Field Education Guide for ordering procedures. For more detailed information regarding the At the transmitting terminal, Request to Send actual configuration of the equipment used on tele­ will activate the data set. When the data set is phone and telegraph lines, you are referred to ready for the terminal to begin sending, it will re­ "Principles of Electricity Applied to Telephone and turn a Clear to Send line to the data terminal equip­ Telegraph Work" published by the American Tele­ ment. Beginning with the conditioning of the Clear phone and Telegraph Company. to Send line, a Send Data line may be activated from For more information regarding the Electronic the data terminal equipment to the data set present­ Industries Association Standards, a form on Recom­ ing the bits for transmission. This is the minimum mended Standards 232A is available from the engin­ configuration required for transmitting data. For eering department of the Electronic Industries Asso­ receiving data, we must have a Received Data line. ciation. This publication describes the interface be­ In addition to these basic lines, other data sets tween data processing terminal equipment and data may use Serial Clock Transmit, Serial Clock Re­ communication equipment. ceive. These clockings may be either internally Many Original Equipment Manufacturers' Informa­ generated by the data set or provided from an exter­ tion (OEMI) manuals are available within IBM which nal source such as the data terminal. A Data Car­ pertain to the attachment of IBM equipment to other. rier Detect line will indicate to the data set that a devices. Examples of these are the OEMI manuals complete circuit, or channel, has been established on the IBM 2701, and the IBM 7701, 02, 10, and 1I. with the remote end. You will learn more about the For more information on tele-typewriter fundamen­ additional lines when you study particular machines tals, there is a booklet called "Tele-typewriter utilizing data sets requiring them. Fundamentals Handbook" written by William D. Rex­ The Send Data line to the data set is normally road and available from the Computer Design Pub­ conditioned by the output of the serializing device in lishing Company. the data terminal. Similarly, when receiving, the This completes the study portion of Session 4. Received Data line provides the input to the des erial­ You will now find a group of study questions provided izing device of the receiving data terminal. Some so that you may evaluate whether you have obtained problems that will concern you in this regard are: the principal points from this session. If you do not 1. The data set has accompanying interface answer all of the questions correctly, you should specifications delineating what must be delivered on review this session before proceeding.

34 IBM CONFIDENTIAL REVIEW QUESTIONS 11. Carrier systems use a method lmown as Frequency Division Multiplexing to channelize the 1. A path provided for electrical communications frequency spectrum they occupy. is referred to variously as a a (a) True ______or a ______(b) False 2. This path can be provided only by wires. 12. Both sidebands of a signal must be trans­ (a) True mitted to accomplish satisfactory communication. (b) False (a) True 3. After each of the following channel types, (0) False place the letter corresponding to the correct defin­ 13. Define Modulation in your own words as ition from the right hand listing. applied to Data Sets. Simplex a. Capable of simultaneous transmission and recep­ tion. Half-Duplex ____ b. Can operate in only one 14. Why are 4 kc channels provided when voice direction. signals require only a bandpass of approximately Full-Duplex c. Can send or receive, 200-3000 Hz after filtering? but only one or the other at any given time. 4. The four grades of channels are: (a) ______15. Identify the type of Modulation being presented (b)------in each of the following figures: (c) ______(d) ______5. The code developed for use with printing telegraphic systems is called and consists of ___ data bits plus a ______bit and a 1. 42 unit bit. 6. Cross out the undesired terms in the follow­ ing chart to make each horizontal line of entries correct. Condition Bit Logical State Mark Yes/No One/Zero 16. The agency of the U. S. Federal Government Space Yes/No One/Zero which regulates communications is the If this referred to a telegraphic transmission, the line would be at fullcurrent condition for a (SPACE/ 17. What characteristic of data transmission is MARK). (Underline your choice.) primarily limited by the bandwidth (in Hz) of the 7. In your own words, describe the difference channel? ______between Asynchronous and Synchronous signaling. 18. What minimum grade of channel would be required to transmit data at each of the following bit rates? 8. In your own words, explain the difference (a) 45 bits per second ______between Serial-Bit and Parallel-Bit transmission. (b) 135 bits per second ------(c) 1800 bits per second ______(d) 200 to 600 bits per second -----_ 9. What is the name of the new term which has 19. Refer to the Line Voltage vs. DBM chart been adopted to replace the term "cycles per sec­ provided in the text and give the peak-to-peak volt­ ond" ? ages that would be displayed on an oscilloscope for a 1 kc signal at each of the following levels on a 600 ohm telephone leased line. 10. A voice channel is how wide in cycles (approx- (a) 0 dbm (b) -6 dbm ____ imately) ? (c) -8 dbm ______(a) 1000 20. Why are "Repeaters" used on: (b) 2000 (a) Telegraph lines: ______(c) 3000 (d) 4000 (e) 5000

IBM CONFIDENTIA L 35 21. The device provided in long distance tele­ 24. Loading Coils are placed in a telephone line phone lines to eliminate the annoyance of hearing to compensate for the ______your own voice coming back to you is called an capacity of the line. ______" This device injects 25. When capacitive, resistive, and/or inductive a problem of Turn-Around time into design of a components are added to a telephone line to improve communications system. What is meant by Turn- its characteristics from the standpoint of attenua­ Aroundtime? ______tion and/or phase distortion, the components thus added are referred to as ______26. The reference of decibels as used in tele- phone work is ____watts dissipated in a load of ______ohms. How may Turn-Around time affect the throughput of 27. What is the advantage of a "Conditioned" a system ? ______telephone line over an unconditioned line? ____

22. What two undesirable characteristics of tele­ phone lines are eliminated (or at least improved) through the use of Companders? (1) ______(2) ______28. The Data Set converts the output of a Busi­ ness Machine (Data Terminal) to a form which will 23. A compander provides (little/great) amplifica­ be accepted by the ______tion of weak signals and (little/great) amplification when sending. of strong signals, on the sending end which consti­ 29. The two principal functions of a Data Set are tutes (Compression/Expansion) of the signal level on ______and ______the line. (Underline your choices.)

36 IBM CONFIDENTIAL SESSION 5

,COMMUNICATIONS SYSTEMS CONTROL

You should understand the following concepts after completing of this session: Message routing and control including line access, formating, record keeping, error control, priorities and terminal operating modes.

Highlights

• Message Types - Single Address, Multiple, Group, Broadcast. o Message Switching - store and forward. Manual Semi-automatic Automatic o Circuit Switching - immediate line routing. o Selective Calling and Polling - to overcome "Contention" problem. o Addressing is direction to receive. • Polling is direction to send. • Intercept of messages for reroute to active terminal. G Editing of messages for sequence control and record keeping. o Examination of messages for priority, to determine status in "queue. " o Logging of traffic, Journal or record of transmissions. o Error Control, answerbacks. o Terminals in Control Mode and Text Mode.

The requirements for control of a data commun­ The Control Center of a network may handle ication system will be explained with reference to several types of message. Figure 19. 1. Single address message - intended for trans­ The block labeled "Communications Control" mission to only one remote terminal. must analyze each message to be sent or received 2. Multiple Address Message - requires trans­ to determine its proper routing. This information mission to more than one remote terminal. is usually contained in the heading of -each message. 3. Group Address Message - requires trans­ For messages to be sent, there will normally be a mission to a predetermined group of remote termin­ "destination code" which represents the unique ad­ als. dress of some remote data terminal. 4. Broadcast Message - requires transmission to all remote terminals. Messages may be sent as they are readied by the Control Center or they may be saved until a re­ quired number has been accumulated, or until a pre­ determined interval of time elapses. This is called "Queueing." Queueing permits more effective util­ Communications ization of communications channels. Control The function of "routing" must be performed in any data communication system, but Queueing is used with Message Switching Systems. Other types of systems include: Circuit Switching, and Selective FIGURE 19. COMMUNICATIONS NETWORK Calling and Polling.

IBM CONFIDENTIAL 37 MESSAGE SWITCHING SELECTIVE CALLING AND POLLING

Mes'sage Switching is used by the Control Center to When two or more terminals are operating on the transfer messages from one channel or circuit to same circuit; all terminals will receive all mes­ another. In Figure 10, a message from terminal 8 sages whether intended for them or not. This prob­ to terminal 2 would require that the Control Center lem can be overcome through "Selective Calling." completely receive the message from terminal 8 and This means that only the called terminal will copy then retransmit it to terminal 2 on a different chan­ the message. If more than one terminal tries to nel. This method of switching is also referred to as send at the same time, a condition called "Conten­ "store and forward." In telegraph-oriented systems, tion" arises. That is, multiple terminals are con­ three versions of this are employed: tending for the facilities of the Circuit or Channel. 1. Manual Torn-Tape Switching This problem can be eliminated by "polling" which 2. Semiautomatic Switching is a controlled invitation to send. 3. Automatic Switching Some systems have automatic mechanical polling devices which will sequentially permit each terminal Manual Torn-Tape Switching to send. This function can also be performed through programming by a computer. Each terminal as it is In a data communications system using this form of polled is expected to answer. If the terminal does switching, a message is received in punched paper not have any message to send, it will answer with a tape at the Control Center. The Origin and Destina­ "negative" response. If the terminal has messages tion codes are examined and the tape is then trans­ (also called traffic) to send, it will respond to the ferred by the operator to a tape reader for trans­ poll by sending its queued messages. Failure of a mission on the proper outgoing line. terminal to respond to a poll, indicates that it is in­ operative or nonexistent. The programmer and the Semi -automatic Switching Computer Control Center may elect to try again and/ or delete the terminal from the polling table or, he In data communications systems using this form of may leave the terminal in the list and, after waiting switching, an operator checks the destination code a predetermined length of time, go on polling the preceding each paper tape message and, by pressing rest of the terminals. the proper keys on a control unit, causes the mes­ sage to be relayed to the proper destination as it is LINE CONTROL received by the Control Center. In a message control network, each communications Automatic Switching line to the control center is shared by many termin­ als. Since only one terminal can use a line at a In systems utilizing this form of switching, an in­ given time, terminals will contend for the use of the coming message is perforated in paper tape and line, unless some form of supervision is imposed. automatically routed through a tape reader to analyze The control of the lines and terminals is a function the destination address. Circuits are then condition­ of the control center. ed to assign the message to the proper outgoing line Polling is the systematic interrogation of termin­ as it passes through the reader. als in the network by the control center. Each ter­ minal has a unique address, and can be started and CIRCUIT SWITCHING stopped by the control center. A table of terminal addresses is used by the center as a polling sequence. Circuit Switching (also called line switching) does When a terminal is polled, a signal is sent back to not require the receipt and retransmission of mes­ the control center indicating the status of the ter­ sages. The Control Center provides a direct con­ minal. This response, known as an answerback, in­ nection between the terminals desiring to communi­ dicates that the terminal is ready to send, ready to cate under the Control of an operator or automatic receive, or not ready to send or receive. The con­ switching equipment. One common example of Cir­ trol center, in response to the answerback, accepts cuit Switching is the use of the dial telephone. In messages that are ready, sends messages that have this application, dialing the required digits sets been waiting at the center, and proceeds to poll the automatic equipment in operation to connect your next terminal. line directly with the line of the called party. Com­ With terminal and line control responsibility, the pare this with the Message Switching counterpart of control center can restrict or stop polling when sending a telegram which must be received, printed, necessary. For example, if during the normal oper­ and then delivered to the addressee. ational day a momentary burst of traffic exceeds the

38 IBM CONFIDENTIAL handling and queueing capacity of the system, the 2. Hetention of priority addresses in core stor­ control center recognizes this overload and restricts age - In this method, a priority message is placed polling to limit the number of incoming messages. in its normal queue position, but the sequence num­ This procedure allows the total systems traffic to be ber and address location of the message are retained processed, although some delays will be encountered in core storage. during this period because of the system's "flatten­ 3. Transmission prior to logging - This method ing" of the traffic peaks. is based upon recognizing that a message is priority The concepts to be derived here are: type. The message is transmitted to its destination 1. Polling invites a terminal to send. immediately and logged later. 2. Addressing commands a terminal to receive. 4. Priority queues - In this method, special queues are established for priority traffic. Intercept Logging In some cases, messages may be intercepted by the control center. This means they are prevented from Some systems utilize long and short term "Journals" reaching their desired destination. This may occur for retaining messages handled. Retrieval may under program control for the following reasons: require special identification "Keys" to prove 1. Message contains errors. authorization for access to the Journal. 2. Message has incorrect format or heading. Long term Journals are usually Magnetic Tape; 3. Addressed terminal is inoperative. Control intermediate term on disk files; short term in mem­ center reroutes to an alternate terminal at a nearby ory, data cell, or drum files. This method helps in location. determining where an error entered a message and 4. Due to passing from one time zone to another, in repeating messages. the addressed terminal is not yet in operation. The control center will hold the message queued until the Error Control proper terminal comes on line. Normally, procedures will be provided for receiving terminals to answer back to the sending terminal Editing acknowledging correct or incorrect receipt of a message. If the answer-back indicates incorrect The control center may edit incoming messages receipt, procedures usually exist to provide for re­ prior to reroute, such as: transmis sion. 1. Add control center sequence number, date and time to the header. Terminal Operating Modes 2. Receive from an IBM terminal device and change heading for required address to print out There are normally two modes of operation: messages on a telegraphic printer. 1. Control mode 2. Text mode Priorities Control mode is in operation for polling and ad­ dressing while text mode indicates the data handling The control center can examine header information portion of the terminal operating procedures. Some in messages to determine priority or initial or re­ terminal devices also revert to control mode for transmis sion. acknowledgment sequences between messages. The There are several methods for handling priority division between control and text mode usually messages: occurs when addressing is ended. 1. Flagging - Priority traffic can be flagged This completes the text for Session 5. Answer during the header analysis and before the placement the following study questions. If you get them all of the message in the queue. On testing the queue correct, you have conquered the main points of the for traffic to be transmitted, the queue can be scan­ section. If you get any questions wrong, you should ned for priority traffic to be sent before normal review the necessary material before proceding to messages. the next session.

IBM CONFIDENTIAL 39 REVIEW QUESTIONS 8. If a terminal yields a negative answerback to a Poll, the Control Center should drop that terminal 1. In your own words, define the term "Queueing." from its Polling List. (a) True (b) False 9. The Control Center must always follow the same sequence of polling terminals on a line. Spec- 2. In your own words, compare the concepts of ifyWHY. -- Message Switching and Circuit Switching. (a) True (b) False 10. If the terminal for which a message is in­ tended happens to be inoperative, there is no way to send the message to its destination. Specify WHY. (a) True 3. If more than one termi.nal tries to send on (b) False the same line at the same time, what term is applied 11. In a Message Switching system, the Control to this situation? Center can add other information to a message be­ fore it is forwarded to the required addressee. (a) True (b) False 4. What is the difference in terminal operation 12. The Control Center of a Message Switching when being Polled from terminal operation when system must send all messages it has received for being Addressed? terminals in the same sequence in which they were received. Specify WHY. (a) True (b) False 13. What four methods may be used for process­ ing priority messages in a Message Switching sys­ 5. If a terminal has traffic for the Control tem? Center, what constitutes a positive answer to a Poll ? (a) ______(b)------(c) ______(d) ______6. If the Control Center has Polled a given ter­ minal twice in succession, what should it do? 14. Why is a Journal or Log maintained? (a) Continue trying until an answer is re­ ceived. (b) Skip that terminal and proceed to process the remainder of the Polling List. . (c) Stop and wait for operator intervention. 15. Anyone can access all of the messages in the 7. The terminals on a given line must be polled Journal. Specify WHY. and/ or addressed sequentrally by their physical lo­ (a) True cations on the line. (b) False (a) True 16. Describe the difference between Control Mode (b) False and Text Mode.

40 IBM CONFIDENTIAL SESSION 6

IMPL EMENTATION

SERDES AND SHIFT REGISTERS

In this session you will learn in more detail the methods of serializing and deserializing data for transmission and receiving, respectively.

Highlights

o SERDES is a Contraction of Serialize/Deserialize. o Use of "Storage Elements," "Store Control" blocks. o Line Control "Storage Element" and "Bit Timer." o Register is a group of Storage Elements. o In transmit, characters are converted from Bit Parallel to Bit Serial. o In receive, characters are converted from Bit Serial to Bit Parallel. o Characters are TRANSLATED from BCD to 4 of 8 Code on transmit operation. o Characters are TRANSLATED from 4 of 8 Code to BCD on receive operation. o Shift Register moves character up through it while presenting the character one bit at a time to the line instead of leaving the character stationary and sampling it one bit at a time to the line as in SERDES. o "OR Control" accepts either input ON to activate one leg of a Store Control block. o Line over a designated bit means "NOT" or logical zero condition of that bit. (Example: N)

This section deals with two methods of serializing device can be signaled to go into either of its two and deserializing data, and describes how a data set states and will stay that way until signaled to change. or modem responds to data bits. Thus, we require a line to turn the device on, and one to turn it off. The output line from its upper SERDES half is then considered plus (+) if the device is on, SERDES is a contraction of "Serialize/Deserialize." and negative (-) if it is off. The store control block A SERDES device is capable of loading a character merely indicates that a plus (+) condition is neces­ bit-parallel, then dismantling the character and sary on both of its inputs (left hand side) in order to presenting it one bit at a time to the data set for condition its output (right side) plus (+) to perform a transmission. This is Serializing. On the receiv­ turn on function to a Storage Element (T) or present ing end, the SERDES will accumulate bits, one at a a plus (+) level to the data set interface. The blocks time, until a complete character is assembled. labeled "Delay" serve only to provide a difference in This is Deserialize. When a complete character time between the input of the block going plus and the has been assembled, it can be transferred bit-par­ output going plus. This enables us to do certain op­ allel to other circuitry. erations at points within a single bit-time period. Figures 20 and 21 show the machine circuitry The bit times provide a source of sequential pulses necessary to perform these functions. of plus polarity and properly spaced to time the First, examine the notations we are using. The operation. (Comparable to the distributor of an letter "T" represents a storage element. This ele­ automobile ignition system or to a digit selector of ment can be a relay, a magnetic core system, an an accounting machine when the digit selector is electronic latch, or an electronic trigger. The wired as a digit emitter.)

IBM CONFIDENTIAL 41 Conventions ,.....--- + 4 of 8 Char = A Storage Element +On T R, 0, -Off 1---- I+AND[ 1,2,4,8, x, N NOTE: Line Over bit Indicates 1 '------' - No-Bit Condition 2 Line + Off T + Control Serial Bits to Modem ~ Send Data ·W » ~--- -a- T +Mark 2 f---- Figure 29 ----....:...... -- - Space 0- 4 ~ (4 of 8 Code) T ~--- -Fr 0- 4 '------' >--- 8 - T 0- ---- 8 ~ C5 ~- "0 R Bit Parallel 0- -;;; - c: T Input BCD c .= f---- +a- BCD R 0- to 0 ~---- 4 of 8 T ---- +M 0- 0 .-- X ----T '8 0- 1-- -- - X 34 -- 7 ~L--- N ·V- 6 T Bit Time~ 1--- J:r 5 r-±. N f"\ ~ 1'------' Bit 8 4 ~V "---r- ..("\ 3 Bit2 I v 2 Bit 1 1 '

End of Character SERDES Reset

Gate New Character Control Delay -- Delay 2 1

FIGURE 20. SERDES TRANSMIT OPERATION

Transmit Operation ON, at the time the Bit Timer samples the associated AND, a + or Mark will be delivered. If the "T" is Sequentially, the operations to be performed are: OFF when sampled, a no-bit condition exists and a (Refer to Figures 20 and 21) - or Space will be delivered for that bit interval to 1. Reset storage elements (entire group is the Send Data line. called a Register). 4. Slightly after the 8th bit (N) of the character 2. Translate BCD character to 4 of 8 code and is sampled to the Send Data line, Delay 1 will be place it in the register. satisfied and the SERD ES register will be reset 3. Continue running the Bit Timer which will (cleared). sequentially sample the storage elements of the reg­ 5. Later, at the end of Bit 8 time, Delay 2 will ister and transfer the information to the Send Data be satisfied and a new character will be translated line of the Data Set or Modem. Note: If the "T" is and loaded, ready for transmission.

42 IBM CONFIDENTIAL Bit Time 8 1 2 3 4 5 6 7 8 1 The SERDES Register may also be referred to as a Transmitting Data Register (D. R.) or an Assembly/ Reset Reg Disassembly Register (A/D Register). -.n. ~ I-

Set Reg r== ~ I- SHIFT REGISTERS

TI .-J L Another device utilized for serializing and deserial­

T2 izing data is the shift register. It accomplishes the same logical functions as the SERDES. In explaining Shift Register operational sequences, r T4 C Figures 24 and 25 will be referenced. (l) E First, additional conventions of operation must be (l) T8 W established. The Store Control Block requires both (l) m 0 TR inputs to be plus to produce an ON output; but, if the £ --.J I VI upper input leg is negative when the oscillator pulse is generated, then the OFF output line will be con­ TO I ~ ditioned. The OR control is slightly different. If either of the input legs is plus, the output will be plUS. TX I W In the Shift Register, since it is designed for TN higher transmission rates, we have replaced the 1 emitter with an oscillator to provide Bit Timing to line Ctl (T) F- the circuit. To control where we are in the proc­ r-- essing of a character, the counter circuit provides Mark Sp~ce Mark the necessary Bit Time identification. Send Data ~ 2 4 8" N I- 1 R 0 X Shift Register - Transmit (See Figures 24 and 25.)

The sequence of operation follows: FIGURE 21. SEROES CONTROL SEQUENCE, TRANSMIT 1. By Bit Time 1, a new character has been gated through the translator and loaded bit-parallel Receive Operation (See Figures 22 and 23.) into the shift register. 2. The first pulse from the "pulse maker" All data arriving at the terminal from the Data Set or performs the following: Modem appear bit-serial on the Received Data line. a. N bit moves up to "T" X, because TN was These data are applied to all Store Control Blocks at off and no plus condition was available to the the same time. Sequentially, the receiving oper­ Store Control block for "T" X. When the ation progresses as follows: pulse arrives on the lower leg of the Store 1. At the end of Bit Time 8, the entire SERD ES Control block, "T" X turns OFF; however, Register is reset (cleared). during this same period, "T" X was ON, and 2. As the Bit Timer advances to 1, if the Re­ therefore the store control block of "T" 0 is ceived Data line is in a Mark State, the "T" 1 will conditioned ON when the pulse is made and be turned on. ."1''' 0 stays ON, but now "T" X contains the 3. For each additional Bit Time, 2 through 8, N bit and "T" 0 the X bit of the "A" charac­ the appropriate store control (+ AND) will be tested ter in 4 of 8 code. and its associated "T" turned ON, if the Received b. In a similar manner, the 0 bit moves to Data Line is Marking, or will remain OFF if the the "T" R, the R bit moves to "T" 8, the 8 line is spacing. bit moves to "T" 4, the 4 bit moves to "T" 2. 4. Mter time has been allowed for the 8th bit the 2 bit moves to "T" 1 and the 1 bit enters (N) to be stored, Delay 1 times out and the entire the line control T to condition the send data character, which has been assembled by deserial­ line to the Modem at Mark level (+). ization, is gated through the translator and presented 3. For each succeeding pulse, the bits in the to the machine circuitry as BCD. shift register advance one position until Bit Time 8 5. At the end of the 8th Bit interval, the SERDES when the N bit is delivered to the Line Control "T" Register is reset and we are ready to receive another and another new character is loaded for transmission. character.

IBM CONFIDENTIAL 43 Figure 29 (Receiving Letter A = 1, 2, 4, 8, R, 0, x, N (Serial Bit Input) in 4 of 8 Code) Received Data /Tom Modem + Mark (4 of 8 Code) - Space Register + +On ~------ol - Off T +

Storage

2 T

2 Bit IT Parallel Store 4 Output + Control T (BCD) ~ 4 (Conventions) 8 T

8 5 + ~ Bit 1 ec I------CA T I- + Bit 2 R Bit 3 + ~------

T

N

End of. Char Dump Control

-----2--"7 Reset SERDES (Ready to Receive Again)

FIGURE 22. SERDES RECEIVE OPERATION (A)

44 IBM CONFIDENTIA L Bit Time 8 1 2 3 4 5 6 7 8 1 Shift Register - Receive (See Figures 26 and 27.)

Translate The operational sequence for receive follows: ~ .M...-I- 1. At Bit Time 1, the Receive Data line is at Reset Reg Mark (+). When the pulse is generated, the 1 bit ~ IIf----- from the line is set into "T" N and all of the other TI Storage Elements are reset OFF since their cor­ f----- L f----- responding Store Control blocks are not conditioned T2 ON. 2. At Bit Time 2, the 2" bit from the line is set T4 in "T" N and the 1 hit moves up to "T" X. Ii: 3. For each succeeding Bit Time, the Receive OJ E T8 OJ Data line condition is entered in "T" N and all other W OJ bits in the shift register are shifted up one position m 0 TR until at Bit Time 8; the 1 bit arrives in "T" 1 and a ~ L f----- V) complete character is identified by the Counter. TO 4. The assembled character in 4 of 8 code is L f----- then gated bit-parallel through the translator to TX L other machine circuits in BCD in Bit-parallel mode. f----- 5. Accumulation of next character begins. 1 TN The specific timings and circuitry of the Shift Reg­ Mark Space Mark ister, as employed in Teleprocessing equipment, will - Rec Data ~ vary somewhat from this conceptual shift register - 2" 4 "8 N 1 R 0 X due to requirements of the particular components from which it is constructed as well as to the actual speed at which it must operate. FIGURE 23. SERDES CONTROL SEQUENCE, RECEIVE This completes the text for Session 6. If you can answer all of the review questions correctly, you may go on to Session 7. If you answer any questions incorrectly, review the appropriate sections of the text before proceeding.

IBM CONFIDENTIA L 45 + Line Control Send T On Data Off T + ---Y

+Mark(On} 29 -Space(Off} 4 of 8 Output T Bit-Serial

4

BCD Input Store Bit Parallel Control 0 + On "0 v; c: + 0 ~ T ~ R

+

+ +

OR Ctl ~ ~

Count 7+ Time Gate Translator Oscillator (Timing)

n..JU1..J ~ (Local or from Modem) 11 1 21 3 I I 8 A = 1, 2, 4, 8, R, 0, x, N in 4 of 8 Code

FIGURE 24. SHIFT REGISTER - TRANSMIT OPERATION (A)

46 IBM CONFIDENTIAL 1 2 3 4 5 6 7 8 Bit Time l 8 1 (Caunter Va lue} Osc ~ r-L rL M-iLrt.- ILM- ~ M- Pulse Maker IL-lL-L L L M-IL-tL-L L

Send Data I Mark Space !---- Marks -On 1 2 4 8 R 0 X N Line Ctl Off ~ I-- ~ I ~ 1 R 0 X jI 2 R 0 IX / 3 R 0 [IX I 4 - R 0 IjIX I R R 0 ~X I o 0 [IX

X ~X

N

Gate 8.1 7· 8.1 Translator F

FIGURE 25. SHIFT REGISTER, CONTROL SEQUENCE, TRANSMIT

IBM CONFIDENTIAL 47 +

BCD Out T Bit Parallel

8

R +

+

Figure + 29 Received Data T X + Mark, - Space ( 4 of 8 Input X Bit Serial)

Synch (Local or from Modem) Letter A I, 2, 4, 8, R, Osc = ~ 1/2 Bit Out of Step with 0, X, N in 4 of 8 Code Gate Translator Out Transmit Osc.

FIGURE 26. SHIFT REGISTER - RECEIVE OPERATION

48 'IBM CONFIDENTIAL Bit Time (Counter 8 2 3 4 5 6 7 8 Value)

Osc

Pulse Maker

Rec Data

2

4

8

R

o

x

N

Gate Translator

FIGURE 27. SHIFT REGISTER, CONTROL SEQUENCE, RECEIVE

49 IBM CONFIDENTIAL REVIEW QUESTIONS 13. How does the Shift Register know it has trans­ mitted a whole character and that it is time to load 1. What does SERD ES stand for? ______a new one? ______

2. The primary function of SERDES when trans- 14. In which Storage Element is the "X" bit of mitting is to convert characters from ______the character "A" (In 4 of 8 code) at Bit Time 3 on bit to bit format. Transmit? ______3. The primary function of SERDES when receiv­ 15. At Bit Time 3, the Send Data line will be at ing is to convert characters from __-----_ (Mark/Space) and represents the ______bit to bit format. bit of the "A" character in transmit operation. 4. If a Store Control block has only one of its 16. At Bit Time 3, in receive operation, the "1" input legs ON, the output will be (ON/OFF). (Under­ bit of the "A" character is in the ______line choice.) Storage Element and the Received Data line is at 5. If a Storage Element is turned ON when a (Mark/Space) representing the bit of character is loaded for transmission, at what Bit the "A" character. Time will it be turned OFF ? ______17. How does the Shift Register recognize that a complete character has been assembled and is ready 6. Briefly describe why the Line Control Storage for Bit Parallel transfer through the Translator to Element is necessary. ______the rest of the machine? ______

7. The Translator used in the example in the 18. Briefly describe the difference in the way text converts code to. ______the SERDES and the Shift Register accomplish Ser­ code on transmit operation. ialization on Transmit. 8. Why is Delay 1 provided in transmit? ___

9. Why is Delay 2 provided in transmit? ___ ~9. Briefly describe the difference in the way the SERDES and the Shift Register accomplish De­ serialization on receive. 10. The line is a (Mark/Space) at Bit Time 7. (Underline choice. ) 11. Shortly after the beginning of Bit Time __ , the completely assembled (deserialized) character is transferred in bit form through the to the remainder of the ma- chine circuits on receiving operation. 12. If both input legs are ON or only one input leg is ON, of an OR Control block, the output will be (ON/OFF). (Underline your choice.)

50 IBM CONFIDENTIAL SESSION 7

IBM LINE ADAPTER

This session will provide you with an understanding of IBM's Modem equipment (one type) and how it can provide the interface function between a Serialize/Deserialize device and the communications line for transmit and receive. The student should also become aware of some of the equivalent components (R, L, C) of a transmission line and their effect on the transmission of data via the line.

Highlights

• IBM Line Adapter, IBM Modem are similar terms. • Line Adapter converts serial data bits from square wave to two different frequencies representing Mark and Space which can be handled by the communications channel. • Line consists of distributed Inductance, Capacitance and Resistance. o Line components attenuate the two frequencies used by different amounts. Causes amplitude loss of Space frequency. o A Delay occurs in the propagation of the signal from the sending modem to the re­ ceiving modem because of line characteristics. o Line Distortion of the sine wave signals of the Mark and Space frequencies may cause extraneous bit pick-up and resultant errors at the terminal.

In previous sessions, we discussed the required represent a Space (and cause emission of the higher function of a Data Set or Modem. We have estab­ frequency signal by the Modem) and a negative polar­ lished the minimum control lines for interfacing the ity signal to represent a Mark (and cause the Modem Data Set with the Data Terminal and also those for to emit its lower frequency signal). These are the the connection of the Data Set to the Communications actual signal levels used in the IBM 1050. facility. The IBM line adapter (Modem) is a device The communication facility (telephone line or performing the functions of a Data Set but it is sup­ channel) has been presented in "lumped-constant" plied by IBM instead of the Common Carrier. form. A telephone line comprises DC Resistance, In the preceding section, the operation of as well as Inductive and Capacitive reactances. SERDES and Shift Registers has been explained. These characteristics cause a condition called Now, examine how we can hook up a complete data communication link between two terminals. (See Figure 28.) The Data Terminal at A develops data for transmission to Terminal B. The SERDES of Terminal A will deliver serialized data to Modem 1 Data Data for conversion to a signal capable of being trans­ Terminal Terminal CD Line Facility mitted over the line facility (C). The form in this Vl Vl W \.U Cl MODEM MODEM case is two different Audio frequency sine wave sig­ A a:: ~ B w #1 #2 \.U nals. The low frequency signal represents a Mark Vl C Vl and the higher frequency signal represents a Space. In Figure 29 Compare Line "Send Data" with line AA CD = Send Data from SERDES to MODEM and note that AA is a sample of the output of the (]) = Recd Data from MODEM to SERDES Sending Modem as it would appear on an Oscillo­ scope. Note also that, at this point, we have an in­ put signal to the Modem which is of plus polarity to FIGURE 28. IBM LINE ADAPTER APPLICATION

IBM CONFIDENTIAL 51 .on in which all signal frequencies do not Detail "C - C" vith the same efficiency on the line. In our the higher frequency signal is attenuated; ~, a lower amplitude of signal for the higher frelJ.uency than that developed for the low when ob­ served with an oscilloscope at point BB and shown in line BB of the Chart. Note also the time delay involved to propagate the signal from Terminal A to Terminal B as shown by the arrows X. The amount of delay and the attenuation of the signal are func­ tions of the telephone line. The Received Data line represents the data signal which will be delivered by Modem 2 to Data Terminal B. In line AA of Figure 29, note section C-C' and Acceptable examine this in detail in Figure 30. The wave shapes at A, B, and C are oscilloscope representations of the signal on line during a Mark period. (A Space interval could have been used also). The line A shows an Ideal wave shape but B is still acceptable. If a signal such as pictured in line C is received, errors will result. See 1 of line Band C in Figure 30. In line B, the signal levels off and then contin­ ues to rise - no actual change of polarity (direction) C Unacceptable but in line C at point 1, the signal actually changes direction. This change of direction is due to distor­ tion usually created by the line facility or due to improper Termination of the line in the Modem. It FIGURE 30. LINE ADAPTER WAVEFORMS causes extraneous bits to be detected. The fore­ going will briefly introduce some of the new problems you will have to work with and analyze in maintaining Teleprocessing equipment. This completes the text for Session 7. If you can answer the following review questions correctly, questions incorrectly, review the appropriate sec­ you may go on to Session 8. If you answer any tions of the text before proceeding.

Send Data - Mark Received Data - Mark

Equivalent af Telephane line ~ ______~A ______~

MODEM MODEM (IBM) (IBM) #1 #2

Bit Periads r----j----+-----1f----+---4----I------t----t.----+----

Send Data ~----..------~+EO ~---+-~-~--~ -E

AA

BB

+E Rec Dala -=E

FIGURE 29. IBM LINE ADAPTER, LINE, SIGNALS

52 IBM CONFIDENTIAL REVIEW QUESTIONS 4. The loss in amplitude of the Space frequency as compared to the Mark frequency is partly due to 1. When used with customer owned or leased ______distortion of the line. lines, the IBM Line Adapter performs the same 5. If the signal shown in Figure 30, line C is function as a common carrier ______presented to the receiving modem (line adapter), ______will probably result. 2. The bits and no bits of the data stream pro­ 6. As delivered to the SERDES on receive, the duced by the SERDES on transmit are presented to signals on the Received Data line are ______the communications line as two different _____ polarity for Space and polarity for Mark.

3. The low frequency of the Modem corresponds to a condition of the signal from the SERDES.

IBM CONFIDENTIAL 53

SESSION 8

DATA CONTROL OF MODEMS (DATA SETS)

This session will familiarize you with the modes of Data Set control as far as input and output signals between the data set and the data terminal are concerned.

Highlights

o Bi-Polar-signals relative to Signal Ground. o Uni-Polar-Single Polarity relative to Signal Ground. o Current-Change in current instead of voltage.

Basically, there are three methods of presenting Modem. Example: (1) 0 current equals Space, 62 data to, and receiving data from a Modem: Milliamperes equals a Mark, (2) 20 Milliamperes 1. Bi -polar mode equals a Space, 5 :Milliamperes equals a Mark. 2. Uni-polar mode Various types of Data Sets will use different 3. Current mode versions of these basic modes. This completes your text material on Implemen­ Bi- Polar Mode tation which has included SERDES, Shift Registers, IBM Line Adapter and Data Control of Modems. Bi-polar mode indicates that the data lines between This material represents the practical applications the Terminal and the Modem swing plus and minus of the concepts developed in the preceding sections symmetrically with respect to a zero reference. and is intended to familiarize you with some of the Example: ±E relative to 0 Volts for IBM Modem. different concepts you will be working with in main­ taining Teleprocessing equipment. Uni -Polar Mode Teleprocessing is a field of unlimited develop­ ment and capable of presenting an unending challenge This mode indicates that the data line swings from to the Customer Engineer who wants to stay abreast zero reference to a single voltage level (either plus of technological developments of space age commun­ or minus polarity) to represent Marks and Spaces. ication. Example: 0 Volts (signal ground) could be a Space This completes the text portion of Session 8. while +6 Volts could represent a Mark. Answer the review questions and proceed to Session 9. The following review questions are provided so Current Mode that you may determine for yourself whether or not you have learned the principles presented in this ill current mode data delivery, the presence of section. If you give any wrong answers, you should Marks and Spaces is indicated by a change in current review the necessary sub-topics. level exchanged between the data terminal and the

IBM CONFIDENTIAL 55 REVIEW QUESTIONS

1. A signal input or output which swings posi­ tive and negative around a reference is considered as mode of operation. 2. A signal which swings in only one direction relative to reference is considered a ______mode operation. 3. If the signal condition representing a Mark is denoted as 62.5 milliamperes of current and a Space is 0 milliamperes, then mode is indicated.

56 IBM CONFIDENTIAL SESSION 9

COMMUNICATIONS FACILITIES

This session is provided to familiarize you with some of the available facilities for communications, by whom they are provided, and the agencies that control these offerings.

Highlights'

• Common Carriers defined. o The Federal Communications Commission controls domestic interstate and interna- tional communications. • State Utilities Commissions control intrastate communications. o International Telecommunications Union, of which CCITT and CCIR are portions, provides international efforts aimed at standardization and coordination. o Common Carriers and their services: Bell System General Telephone and Electronics Independent Telephone Companies Western Union American Cable and Radio Corporation. RCA Communications, Inc., Privately Owned Communications Systems

COMMUNICATIONS COMMON CARRIERS availability of service, billing arrangements, chan­ nels and related devices pertinent to data trans­ Communications common carriers are companies mission. which furnish communications services to the public. THE FEDERAL COMMUNICATIONS COMMISSION They are regulated by the Federal Communications Commission or appropriate state agencies. Their The Federal Communications Commission, an in­ services include communications facilities for VOice, dependent federal agency, regulates interstate and data, facsimile and printed messages, as well as internatiorial communications originating in the appropriate communications channels for television, United States, such as radio, telephone, telegraph, telemetry and telephoto. In the United States approx­ facsimile, telephoto and other broadcast program imately 2, 800 companies are recognized as com­ transmissions by wire, cable or radiO. munications common carriers. These companies The Communications Act, establishing the Fed­ can provide complete communications services to eral Communications Commission, requires that the subscriber including channels, modulating equip­ every subject common carrier furnish service at ment, and the necessary terminating arrangements. reasonable charges upon reasonable request. No Alternatively, the customer may lease only the carrier may construct, acquire or operate inter­ channels and provide purchased or leased terminals state or foreign facilities originating in the United equipment for data communications. States without the approval of the commission. The services mentioned in this section are pre­ Under the provisions of the Communications Act sented as a survey of some of the communications every common carrier must file with the commis­ facilities available today. The representatives of sion schedules showing all charges, practices, the communications companies should be consulted classifications and regulations for interstate com­ in order to obtain current information on rates, munications services offered to the public. These

IBM CONFIDENTIA L 57 schedules, lmown as tariffs, are normally filed at THE BELL SYSTEM least 30 days before their terms become effective. The tariffs form a significant part of the machinery The parent company of the Bell System is the Amer­ by which the commission enforces the duties and ican Telephone and Telegraph Company, incorpor­ prohibitions imposed on the common carriers for ated in 1885, which owns all or part of the stock of the benefit of the public. They are also the basic 23 associated operating telephone companies and the contract between the common carrier and the user. Western Electric Company. Together with Western Telephone and telegraph companies are not required Electric, AT&T owns the Bell Telephone Labora­ to file tariffs of their own if they concur in the tariffs tories. Western Electric manufactures, purchases, filed by other common carriers. Due to local con­ distributes and installs equipment to fit the needs of ditions, however, tariffs may vary from company to the Bell System. The Bell Telephone Laboratories company. carryon centralized research for the Bell System. One example of a tariff with a high degree of The people of the Bell Telephone System design, concurrence among a large number of telephone build, operate and maintain facilities for approxi­ companies is tariff #245 filed with the Federal Com­ mately 67 million telephones in 48 of the states and munications Commission by the American Telephone the District of Columbia. Bell System lines connect and Telegraph Company. This tariff covers the V-H with telephone systems in all 50 states of this coun­ Measuring Plan. It establishes the basis for deter­ try and throughout the world. mining the cost of a telephone call by providing a The Bell System provides a wide range of pro­ uniform means of calculating the distance between ducts and services to fit specific communications the calling station and the receiving station. In the needs, from the basic telephone instrument to DATA­ V -H Measuring Plan, each area in the United States PHONE* Service which enables business machines and Canada is assigned a mathematical coordinate to communicate via the telephone network in the on a vertical. (V) and a horizontal (H) basis. This same way people do. The technological contribu­ divides the entire area into a series of small tions of the Bell System Include the invention of the squares, each having an equivalent of latitude and transistor and the solar battery, as well as the de­ longitude. The distance for billing purposes in air­ signing and building of the Telstar satellites. line miles between any two points can then be calcu­ Touch-Tone calling which will replace the rotary lated from these coordinates. dial with push buttons, and completely electronic telephone call switching are being developed to im­ STATE UTILITY COM].'.1ISSION prove the service of the Bell System to its customers. Some of the communications services of the Bell Intrastate common carrier communications service System are Wide Area Telephone Service (W A TS), is subject to regulation by state commissions simi­ Telpak, Teletypewriter Exchange Service (TWX) and lar in function to the Federal Communications DATA-PHONE Service. Commission. WA TS. -- Wide Area Telephone Service is arranged INTERNATIONAL TELECOMMUNICATIONS UNION for subscribers who make many outgoing long dis­ tance calls to many points. Monthly charges are The International Telecommunications Union is an based on the size of the area in which the calls are administrative international organization responsible placed, not on the number or length of calls. Under for the allocation, registration and utilization of the the WATS arrangement, the United States is divided radio frequency spectrum. The main objective of into six zones. The subscriber is billed a flat rate the union is to maintain and develop international according to the zones to be called on a full-time or cooperation for the improvement and rational use of measured-time basis. This can be an advantageous communications. The union undertakes studies and arrangement for data transmission. issues recommendations for the benefit of all mem­ bers, as well as participating in the Technical TELPAK. -- Telpak service is a pricing arrange­ Assistance Programs of the United Nations. Within ment that makes available wide band communications the ITU, the Consultive Committee on International channels of various sizes suitable for large-volume Telephone and Telegraph (CCITT) and the Consultive point-to-point transmission of data, voice, teletype­ Committee on International Radio (CCIR) are actively writer, facsimile, or other services for a flat-rate engaged in the standardization and coordination of regardless of usage. Telpak can be used as a single international worldwide communications facilities. large channel or a group of smaller channels. For

*Trademark of American Telephone and Telegraph Company

58 IBM CONFIDENTIA L example, a Telpak "A" channel may be divided into Western Electric equipment will be used in most in­ 12 voice grade channels. stances where GT&E does not manufacture equiva­ lent equipment. GT&E equipment will be compatible Teletypewriter Exchange Service. -- Teletypewriter with the equivalent Bell System equipment, where Exchange Service (TWX) provides direct dial point­ required, to allow direct interconnection of services. to-point connections using input/output equipment Special arrangements will be available when required such as page printers, keyboards, paper tape readers to meet individual requirements. and paper tape punches. INDEPENDENT TELEPHONE COMPANIES DATA-PHONE Service. -- DATA-PHONE Service provides for the transmission of data between a var­ The General System and balance of the 2,800 tele­ iety of business machines, using regular local or phone companies operating 13 million telephones in long distance telephone networks, or WATS lines. the United States provide services that interconnect The cost to the customer is the same as an ordinary with the Bell System and each other. Over 150 in­ telephone call in addition to a monthly rate for the dependent telephone companies have more than DATA-PHONE data set. 10,000 subscribers, and another 100 have more than 5,000 subscribers. Other Services. -- In addition to the familiar dial The United States Independent Telephone Associ­ telephone services, voice grade and telegraph grade ation (USITA), with headquarters in Washington, lines can be leased for the exclusive use of the sub­ D. C., represents many of the independent telephone scriber. companies. It provides guidance to its members and coordinates their practices through committees. GENERAL TELEPHONE AND ELECTRONICS COR­ "Telephony Magazine", published weekly by the PORATION Telephony Publishing Corporation of Chicago, and "Telephone Engineer and Management", published General Telephone and Electronics Corporation is a semi-monthly by the Telephone Engineering Publish­ highly diversified communications and manufacturing ing Corporation of Chicago, are important vehicles enterprise whose operations throughout the United for distributing information about the telephone in­ States and abroad are known as the "General Sys­ dustry. Both companies publish annual directories tem". GT&E provides communications services indicating the corporate structure and pertinent ranging from telephone service for the home and statistics about telephone companies in the United office to highly complex voice and data systems for States. industry and national defense. The company has approximately 5-1/2 million telephones in more WESTERN UNION than 30 domestic telephone operation subsidiaries and three international subsidiaries located in The Western Union Telegraph Company, incorpor­ British Columbia, the Dominican Republic and Haiti. ated in 1851, has played a vital role in the develop­ Automatic Electric Company, a subsidiary of ment of communications in the United States. GT&E, produces communications equipment for the The company furnishes communications services independent telephone industry. Lenkurt Electric by wire and microwave radio throughout the United Company, Incorporated, another subsidiary, manu­ States and by ocean cable between the United States facturers data sets, microwave radio, and carrier and foreign countries. It provides the only national multiplexing equipment for commercial and military telegraph message service. It also furnishes custom­ communications. built private wire systems and facsimile systems on The General System has had broad and extensive a leased basis and Telex, a direct-dial teleprinter experience in the data communications field. Over service. the years, it has provided a wide variety of services Western Union leases more than 2,000 private making use of channels ranging from narrow band wire systems of varying sizes and speeds for indus­ telegraph up to four-megacycle video channels. Its try and government. It recently placed in service services include teletypewriter services in its oper­ for the Department of Defense the world's largest ating territories and direct dial TWX operations. and most advanced digitar data network with a capa­ It is the General System's intention to offer, city of 7,000,000 punched cards, or the equivalent under tariffs, all data services of the common car­ of 100,000,000 words daily. riers including wide band Telpak channels. The ter­ Western Union recently expanded its offerings minal and hardware equipment utilized in providing of leased wire facilities to include a full range of data communications will be developed and manufac­ voice, alternate voice-record, Telpak and voice­ tured by GT&E subsidiaries where practicable. data services. It also leases circuits and equipment

IBM CONFIDENTIA L 59 to speed communications by facsimile. suhscribers in London or Paris, for example, with­ Scheduled for operation by Western Union in 1964 out any operator intervention whatsoever. is a new coast-to-coast microwave system which will be capable of accommodating all modern forms of RCA COMMUNICATIONS, INC. communication at high speeds and in large volume .. The Radio Corporation of America was created in It will be used to transmit vOice, facsimile, and 1919 to provide international communications facili­ high-speed data as well as public message and pri­ ties. Ten years later RCA organized a wholly owned vate wire services. subsidiary company, RCA Communications, Inc., to concentrate on the further development of inter­ AMERICAN CABLE & RADIO CORPORATION national radio communications. In recent years RCA has augmented its global radio facilities with coaxial American Cable & Radio Corporation (AC&R), a cable channels to Europe, Puerto Rico, Hawaii, subsidiary of International Telephone and Telegraph, Bermuda, and Jamaica. Since 1962 the company has owns and operates an international telegraph system significantly added to its cable facilities across the with both cable and radio facilities. AC&R was Atlantic and has acquired extensive facilities through­ formed when the operations of four IT&T affiliates, out the Pacific. RCA also plans to expand its cable All America Cables and Radio, The Commerical facilities to South and Central America in the very Cable Company, Mackay Radio and Telegraph Com­ near future. pany, and Sociedad Anonima Radio Argentina Today RCA's global communications network (Buenos Aires) were consolidated. The company comprises almost 1000 radio and coaxial cable chan­ later acquired control of Globe Wireless, Incor­ nels providing telegraph service to the entire world, porated. Telex service to 105 countries, and Radiophoto AC&R, in addition to its operating centers loca­ service to 53 foreign terminals. In addition, RCA ted in New York, Washington, and San Francisco, operates the terminals of 14 radiotelephone circuits maintains and staffs more than 110 overseas traffic in the Pacific area and provides two-way Program offices, as well as seven marine radio stations. In Transmission Service for broadcasters to almost the three "gateway" cities of New York, Washington, any point on the globe. The company also maintains and San Francisco, the public deals with AC&R dir­ facilities for communication with ocean-going ves­ ectly. Customers outside these cities use AC&R sels and ships plying inland waterways. international facilities through the intermediate tele­ RCA Communications furnishes private leased­ graph or teleprinter services of the domestic channel communication services to all parts of the carriers, Western Union and the TWX Bell System. world for commercial and governmental customers. This applies to telegraph and Telex service, as well More than 210 such channels for teletypewriter, as to leased channel operation. telephone, facsimile, and data communications are AC&R's communications network now includes in use. New facilities are being designed to meet more than 500 cable and radio channels, extending the needs of proposed transoceanic data processing across the Atlantic to Europe, down through the systems. In New York a wholly automated telegraph Caribbean, Central and South American areas, and terminal will electronically route, process, and out to the Far East. Through the cable network, its transmit telegrams. RCA now provides automatic own radio facilities, and by connection with foreign Telex service between the United States and Belgium, cable and telegraph companies, the IT&T/AC&R Japan, the Netherlands, Switzerland, United Kingdom, Communications System not only connects the United and West Germany. Subscribers to the RCA Telex States with practically all countries of the world but network simply dial the number of their overseas also furnishes communications between countries correspondent after dialing an area code as in direct outside the United States. distance dialing in the United States. Tll Telex, This worldwide network provides customers however, the calls are on a teleprinter. These in­ with regular message service, press-cast service ternational connections are now established, sub­ radiotelephone service, Telex, Datatelex and leased scriber to subscriber, within seconds. Datatelex channel service. service provides for data communications between AC&R technical activity in the communications the United States and Great Britain on a call-up field is demonstrated by its installation of the first basis. RCA has recently extended Datatelex service automatic Telex switching centers in the United to Hawaii ~nd plans to make it available to other States. AC&R Telex customers may call direct to overseas points when the demand arises.

60 IBM CONFIDENTIAL PRIVATELY OWNED COMMUNICATIONS SYSTEMS

The federal government and some industries pur­ chase, maintain and operate some of their commu­ nications facilities. Examples of these private sys­ tems are telegraph and telephone systems owned by railroads and pipeline companies operating in re­ mote areas. Licenses can be obtained to operate private radio and microwave systems under certain circum stance s.

IBM CONFIDENTIAL 61 REVIEW QUESTIONS 6. What do the following abbreviations stand for? (a) WATS ______1. Define Communications Common Carrier. (b) TWX ______7. What kind of service is Telex?

8. How many voice channels can be multiplexed 2. Schedules showing charges, practices, reg­ on one Telpak "A" service? ______ulations and other particulars for interstate commu­ 9. Photolex provides a means for ______nications services must be filed with and approved transmis sion. bythe ______

3. If the communications service is limited specifically to intrastate service, the regulating agency becomes the ______This completes the text of Introduction to Tele­ processing. Contact your course Administrator for the final examination. Your grade on the examination will be your grade for the course. No reference material is to be used and you will have 1. 0 hour to 4. The schedules referred to in question 2 are complete the examination. known as ______5. The CCITT and the CCIR work to provide ______and ______of world wide communications systems.

62 IBM CONFIDENTIAL APPENDIX - TELEPROCESSING GLOSSARY Area, Operating - Separation of most of the tele­ phone company's work into a large geograph­ ical unit. An area functions as a complete AC/DC Ringing - A method of telephone ringing telephone company up to the executive level. which utilizes current having both alternat­ ARQ - An automatic system which provides error ing and direct current components: ac to correction by utilizing a constant ratio code operate a ringer; dc to aid the action of a and a closed loop to request retransmission relay which stops the ringing when the called of mutilated characters as indicated by re­ party answers. ceipt of nonconstant ratio characters. ACK - Aclmowledge. Artificial Load - See Dummy Load. ACU (Automatic Calling Unit) - Unit capable of es­ ASA Code - A standardized code set recommended tablishing a circuit connection upon input of by the American Standards Association for a digital calling sequence from an attached industry-wide use in transmission of infor­ processor. mation. Address - In communication usage, the coded repre­ ASCII - American Standard Code for Information In­ sentation of the destination of a message. terchange, usually pronounced "Askee". An Addressee - The intended recipient of a message. 8-level code for data transfer proposed to Addressing - This is the means whereby the multi­ achieve compatibility between data devices. plexor or control station selects the unit to ASR - Automatic Send/Receive - A teleprinter unit which it is going to send a message. with keyboard, printer, paper tape reader ADU - Automatic Dialing Unit. and paper tape punch, which allows tape to be Aerial Cable - A cable connected to a pole or simi­ produced and edited off line for automatic lar overhead structure. transmission. Aggregate - The transmitted carrier signal which A-Switchboard - A switchboard in a local central consists of the 12 single-sidebands being office, arranged primarily for receiving sent over the transmission circuit. local orders for telephone connections and Alphanumerics - Characters which may be either for completing these orders, either at the letters of the alphabet or numbers. same switchboard or by way of trunks to Ambient Noise - Acoustic noise existing in a room other switching equipment. or other location. Asynchronous - (Start/Stop) Transmission - Trans­ Amplifier - A device which receives energy at a low mission in which each information character level and sends it out at a high level in iden­ is individually synchronized by the use of tical or nearly identical form. See Repeater. start and stop pulses. Amplitude - The size or magnitude of a voltage or Attended Operation - In data set applications, indi­ current wave form. viduals are required at both stations to estab­ Amplitude Distortion - See Distortion Amplitude. lish the call and transfer the data sets from Amplitude Modulation (AM) - Variation of a carrier talk mode to data mode. As opposed to Un­ frequency's amplitude in accordance with an attended Operation. information signal. Attenuation - Decrease in magnitude of current, vol­ Analog - Information varying in amplitude, fre­ tage, or power of a signal in transmission quency or both as opposed to information ex­ between points. May be expressed in decibels pressed by discrete levels. or nepers. Annunciator - A visual signaling device, operated by Attenuation Equalizer - See Equalizer. relays, which indicates conditions of associ­ Attenuator - See Pad. ated circuits. Audio - Frequencies that can be heard by the human Answerback - The response of a data set or terminal ear (usually 50 cycles to 16,000 cycles per to remote control Signals. second) • Answer Lamp - Telephone switchboard lamp which Autodin - (Automatic Digital Network) - The data­ lights when an answer cord is plugged into a handling portion of the military communica­ line jack, goes out when the called telephone tions system. (See COMLOGNET). answers, and lights when the call is com­ pleted. Area, Exchanges - Areas set up for administrative reasons for telephone service covered by a single rate basis. Usually a single city or Babble - The aggregate cross talk from a large large division of town or village. number of interfering channels.

IBM CONFIDENTIAL 63 Balanced-Balanced to Ground - When applied to a Bit Stream - Referring to a binary signal without cable pair or two wire line it means that the regard to groupings by character. impedance to ground as measured from one Black Box - A generic term used to describe an un­ side of the line is equal to the impedance to specified device which performs a special ground as measured from the other side of function or in which !mown inputs produce the line. !mown outputs in a fixed relationship. Band - A range of frequency between two defined Blank - 1. A machine character to denote the pres­ limits. ence of no information rather than the ab­ Bandwidth-Band Pass - The difference, expressed sence of information. It is composed of all in the number of cycles per second, between spacing pulses between the start and stop the two limiting frequencies of a band. pulses. Bank - An aggregation of similar devices (e. g. , 2. In paper tape, it references a feed hole transformers, lamps, etc.) connected to­ without intelligence holes. gether and used in co-operation. In automa­ Blank Coil - Tape (for perforation) with only the feed tic switching, a bank is 'an assemblage of holes punched. fixed contacts over which to establish elec­ Blank Deleter - Device which eliminates the receiv­ tric connections. ing of blanks in perforated paper tape. Baseband - The frequency band which defines an in­ Blind - (Unblind) - The ability of a device to receive formation signal, e. g., the baseband signal selective information of a transmission and is the information vehicle which modulates a be "blinded" or non-receptive to unwanted carrier wave. data such as item description, price, polling Base Frequency - In any wave, that frequency which and addressing characters, etc. is considered to be the most important. In Book Message - A message to be sent to two or more a driven system it would in general be the terminals and is of such a content that the driving frequency while in most periodic originator feels that no destination needs to waves it would correspond to the fundamental be informed of any other destination. frequency. BPS - Bits per second. Base Group - Term used to designate a number of Break - To break, in a communication circuit, is carrier channels combined to form a channel when the receiving operator or listening sub­ bank which will be further modulated to a scriber interrupts the sending operator or final frequency band. talking subscriber and takes control of the Baud - A unit of signaling speed used in data trans­ circuit. mission. It may contain several binary de­ Bridge Tap - An unterminated length of line attached cisions but most commonly is equal to one somewhere along the system. Bridge taps bit per second (bps). are undesirable. Baudot Code - The conventional5-level teletypewriter Broadband - High speed communication channel hav­ code consisting of a start impulse and five ing a bandwidth greater than voice grade character impulses, all of equal length, and channels. a stop impulse whose length is 1. 42 times Broadcast - Simultaneous transmission and recep­ that of the start impulse. Also !mown. as the tion of a message to all receiving locations 7.42 unit code. on a communications service. Bel - See Decibels. Buffer - A system component which permits a change Bellfast - A teletypewriter switching system leased of speed, voltage, or interface characteris­ from AT&T. tic; frequently presumed to include storage Bell Idles - Special Code sent during periqds of non­ capability. activity between data sets (10001000). Bug - A semi-automatic telegraph sending key in Bias Distortion - See Distortion, Bias. which movement of a lever to one side pro­ Bid - An attempt to occupy a line in order to pass duces a series of correctly spaced dots and traffic. movement to the other side produces a single Bipolar - See Polar Circuit. dash. Bit - Contraction of binary digit, the smallest unit Buried Cable - A cable installed under the surface of of information. It has two possible states: the ground in such a manner that it cannot be 1 or O. removed without dif:lturbing the soil. Bit Rate - The speed at which bits are transmitted, Bus - A conductor, or group of conductors, in a usually expressed in bits per second (bauds). switch gear assembly which serves as a common connection for two or more circuits.

64 IBM CONFlDENTIA L Bussback - Term denoting the common carrier's CARRIER NUMBER OF TRANS- action of tying the output portion of a circuit SYSTEM CIRCUITS DERIVED MISSION back into the input portion of a circuit. TYPE (FD = FULL DUPLEX) FACILITY Bustback - A Western Union term. Similar in nature to Bussback. K(Telephone) 12 FD 2-19 GA Cable Busy Test - In telephony, a test made to find out Pairs (Non- whether certain facilities which may be de­ Loaded) sired, such as a subscriber line or trunk, N (Telephone 12 FD Non-Loaded are available for use. or Program) Toll or Ex- change Cables ON (Telephone) 20-24 FD Cable ON/k(Tele- Cable - Assembly of one or more conductors within phone) 12-16 FD Cable an enveloping protective sheath, so con­ TD2(Micro- 600 FD Radio structed as to permit the use of conductors wave) separately or in groups. L1(Tele- 600 FD Paired Coax Cable Branch - Cable which leaves a main cable to phone or reach some secondary point. Program) Cable Coaxial - A cable consisting of one conductor, L3(Tele- 1860 FD Paired Coax usually a small copper tube or wire, within phone or and insulated from another conductor of Program) larger diameter, usually copper tubing or CAX (Community Automatic Exchange) - A small copper braid. dial office serving a community. Cable Distribution - Branch off a feeder cable. CDC - Call directing code - character directing Cable Feeder - Principal cable from a central code - An identifying call, usually two letters, office. which is transmitted to an outlying telegraph Calling, Selective - The ability of transmitting receiver and automatically turns its printer station to direct a call to 'one or more specif­ on (selective calling). ically designated stations. Central Office - A switching center of the telephone Camp-On - A method of holding a call for a line that company where all telephone lines terminate is in use and of signaling when it becomes for a certain exchange area. See Exchange, free. (Also called Clamp-On). Central Office. CARR - Carrier. Centrex - Central office type telephone equipment Carrier - A high-frequency current that can be serving subscribers at one location on a modulated by voice or signaling impulses. PABX basis. The system allows direct in­ Carrier, Communications Common - A company ward dialing, direct distance dialing, console which furnishes communications services to switchboards, etc. the general public, and which is regulated by CHAD - That piece of paper removed in punching a appropriate state or federal agencies. hole in perforated tape. Carrier System - A means of conveying a number of Chadless Tape - Perforated tape with the Chad par­ channels over a single path by modulating tially attached. each channel on a different carrier frequency Chaining - A system of storing records in which and demodulating at the receiving point to each record belongs to a list or group of rec­ restore the signals to their original form. ords and has a linking field for tracing the See TELPAK. chain. Some typical Carrier Systems are: Channel - A path for electrical transmission between CARRIER NUMBER OF TRANS- two or more stations or channel terminations SYSTEM CIRCUITS DERIVED MISSION in telephone or telegraph company offices, TYPE (FD = FULL DUPLEX) FACILITY furnished by wire, radio or a combination of both; also called circuit. B(Telegraph) 10 FD 4 Wire, Open Channel,. Analog - A channel on which the informa­ Wire tion transmitted can take any value between C(Telephone) 3 FD 4 Wire, Open the limits defined by the channel. Voice Wire channels are analog channels. J (Telephone) 12 FD 4 Wire, Open Channel, Four Wire - A two-way circuit using two Wire paths so arranged that the communication o (Telephone) 16 FD 2 Wire, Open currents are transmitted in one direction only Wire on one path and in the other direction on the

IBM CONFIDENTIA L 65 other path. The transmission path mayor Circuit - A physical, metallic connection between may not employ four wires. (See Channel, two points, also called a channel. Full Duplex, Simultaneous Transmission, Circuit Grade - The grades of circuits are broad and Equivalent 4-Wire System.) band, voice, sub-voice, and telegraph. Cir­ Channel, Full Duplex - A circuit capable of trans­ cuits are graded on the basic line speed ex­ mitting and receiving in both directions at pressed in characters per second, bits per the same time. Usually req:l.ires 2 sub­ second or words per minute. scriber loops. (See Channel, Four Wire, Circuit, Multidrop - A circuit interconnecting sev­ Simultaneous Transmission, Non-Simultan­ eral locations that makes information trans­ eous Transmission.) mitted over the circuit available at allioca­ Channel, Half Duplex - A circuit capable of trans­ tions simultaneously. mitting and receiving signals but in only one Circuit Noise Level - The ratio of the circuit noise direction at a time. Usually requires 1 sub­ to some arbitrary amount chosen as a refer­ scriber loop. (See Channel, Two Wire.) ence. This ratio is normally indicated in Channel, Simplex - A circuit capable of transmitting decibels above the reference noise, dbrn, or or receiving in one direction only. The cir­ in adjusted decibels, dba, which signifies a cuit is not capable of being reversed. noise meter reading adjusted to represent the Channel, Two Wire - A two-way circuit for trans­ interfering effect under specified conditions. mission in either direction, but not simul­ See dba explanation under the db heading. taneously. (See Channel, Half Duplex.) Circuit Switch - A communications switching sys­ Channel, Voice Grade - A channel that permits tem which completes a circuit from sender transmission of speech. Usually will pass a to receiver at the time of transmission (as frequency range of approximately 300 to opposed to a message switch). 3000 cps. In data applications, phase dis­ C L - Control Leader. tortion limits the data speeds to 1200 bps or Clamp-On - A method of holding a call for a line less. Suitably conditioned lines, with phase that is in use and of signaling when it becomes equalization, may handle 1600 to 2400 bits free. (Also called Camp-On.) per second. CLK - Clock. Channelizing - The process of dividing one circuit COAM Equipment - Customer communication owned into several channels. and maintained equipment connected to com­ CHAR - Character. munication company lines but not owned by Character - T~e actual or coded representation of a the communication company. The IBM Ter­ digit, letter or special symbol. minal is a good example (even though not Character Density - A measure of the number of owned by the customer). characters recorded per unit of length or Coaxial Cable - See Cable, Coaxial. area. COD - Change of Direction. Character Emitter - An electromechanical device Code - A system of symbols and rules for use in which emits a timed pulse or group of pulses representing information. in some code. Code Conversion - A process for changing the bit Character Printer - A printer in which only a single groupings for characters in one code into the character is composed and determined within corresponding character bit groupings for a the device prior to printing. second code. Character Reader - An input device which reads Code Holes - The information holes in perforated printed characters directly from a document. tape, as opposed to the feed or other holes. Character Recognition - The act of reading, identi­ COMLOGNET - Abbreviation for Air Force Combat fying and encoding a printed character by Logistic Network. See Autodin. optical or other means. Common Carrier - A company that furnishes com­ Character Set - A list of characters acceptable for munication services to the general public and coding to a specific computer or input - out­ which is regulated by appropriate state or put device. federal agencies. Characteristic Distortion - See Distortion, Charac­ Communication - The process of transferring infor­ teristic. mation from one point, person or equipment Characteristic Impedance (Zo)·- The ratio of voltage to another. to the current at every point along a trans­ Communication, Data - The transmission of data mission line on which there are no standing from one point to another. waves. Compandor - Equipment that compresses the out­ going speech volume range and expands the

66 IBM CONFIDENTIAL incoming speech volume range on a long dis­ Crossbar Exchange - An exchange in which switching tance telephone circuit. is done by crossbar apparatus. Composite - To composite a pair of wires used for Cross Fire - Interference between telegraph circuits voice communication is to apply "composit­ that cause the faulty operation of the relays ing" equipment to the pair. It is a means of in a telephone circuit. getting two dc telegraph channels in addi­ Crosstalk - Interference from adjacent communica­ tion to the voice channel on a single pair of tion channels. wires. Crypto - Cryptographic - Usually pertains to mili­ Compressor - Electrical device which compresses tary equipment used for the transmission of the volume range of a signal. classified documents. Comprise Net (Network) - Network, used in conjunc­ CT - Control Trailer. tion with a hybrid coil to balance a subscriber's CTS - Clear to send (return from data set in re­ loop, that is adjusted for an average loop sponse to request to send). length or an average subscriber's set or both, Customer Station Equipment - Telephone company to secure compromise (not precision) isola­ equipment located on the customer's prem­ tion between the two directional paths of the ises. Such as a telephone instrument or data hybrid. ' set. Constant Ratio Code - A code in which all characters Cutting Through - See Switching Through. are represented by combinations having a fixed ratio of ones. Contention - 1. A condition on a multidrop commun­ ication channel when two or more locations Data, Analog - A physical representation of infor­ try to transmit at the same time. mation such that the representation bears an 2. Unregulated bidding for a line by exact relationship to the original information. multiple users. The electrical signals on a telephone channel Continuous Loading - The practice of wrapping a are analog data representation of the original cable conductor with a permalloy tape or voice. wire. Seldom done because of high cost. Data Collection - The act of bringing data from one Control Character - A character used to cause or more points to a central point. May be functions such as line feed, carriage return, in-plant or out-plant. etc., to occur. Data Digital - Information represented by a code Control Switching Points - Collectively, the class 1, consisting of a sequence of discrete elements. 2, 3 offices (Regional, Sectional, and Pri­ Data Gathering - See Data Collection. mary Centers) needed for nationwide dialing. Data Link - D/L - Electronic equipment to perform The greatest number of long distance toll automatic transmission of digital informa­ links required for any subscriber-to-sub­ tion. scriber connection is 7. The average number Data Origination - The translation of information of links required is 3 or 4. from its original form into a machine - Converter - A device capable of converting impulses readable form or directly into electrical from one mode to another, such as analog to signals. digital or parallel to serial. Data Phone - Both a service mark and a trade mark CPS - Abbreviation for "characters per second" and of the Bell System. As the service mark it "cycles per second". indicates the use of the Bell System message Crossbar - Switching system using mechanisms network for the transmission of data. As a called crossbar switches, consisting of rec­ trade mark it identifies the branch of data tangular fields of contact springs operated in sets designed and manufactured for DATA co-ordination by horizontal and vertical PHONE service. members. Data Set - A modulation/demodulation device de­ Crossbar No.1, the earliest type, is a local signed to provide compatibility between, input/ telephone switching system for use in met­ output equipment and communication facili­ ropolitan areas where there is a high per­ ties. It is also referred to as line adapter, centage of interoffice calls. modem and subset. Some manufacturers of Crossbar No.5, the most recent type, was data sets are: designed primarily to serve the residential American Telephone & Telegraph sections of large cities and the fringe areas General System around these cities. Collins Radio

IBM CONFIDENTIAL 67 Lenkurt Electric parallel. Here, the data speeds are Western Union usually referred to as characters per Classes of Data Sets: second. (Bits per second = characters Data sets can be classified according to per second times bits per character.) type (analogue or digital), speed in bits/ Data Set Clocking - This term identifies the service second, characters/second or bandwidth in where the data set (common carrier) supplies kilocycles, synchronous or non-synchronous the time base oscillator for the bit rate of and transmission mode (serial or parallel). transmission. This, is also referred to by These are defined in the following list of IBM as "external clocking" and by the common definitions. carrier as "internal clocking". To avoid Speed: confusion use "Data Set Clocking" or "Busi­ Low - Below 200 bits per second on a ness Machine Clocking". voice channel or more narrow band facil­ DB - See Decibel. ities. In general, use of voice channels DB Meter - A meter having a scale calibrated to is always preferable where distances are read directly in decibel values at a reference short, or where this bandwidth permits level that must be specified (usually 1 milli­ the simplified design of the data set. watt equals zero db). Used in audio-fre­ Medium - 200 to about 2000 bits per sec­ quency amplifier circuits of broadcast sta­ ond on voice channels. New data sets tions, public-address systems, and receiver under development will probably extend output circuits to indicate volume level. this to about 2400 bits per second. D Code - Control characters are sometimes identi­ High - Above 2400 bits per second on fied by this term. They have the configura­ broad band facilities such as: tion, 1 and R and X and not 0 or 0 and not X TELPAK A 48 kc and not N. TELPAK C 240 kc D=l. R. (OX + XO). N TELPAKD 1000 kc (or 1/2 TD DCT - Dibit Clock Transmit (data set interface). 2 Channel) Dead Line - A telephone circuit disconnected from a Video Channel central office. NOTE: The bandwidths shown above Decibel - 1/10 Bel - The unit used to express power are carrier system bandwidths and ratio: db = 10 log P 1/P2, where PI and P2 the customer signals (baseband) must are the two powers being compared; for ex­ be limited to more narrow spectrums, ample, 3 db down (-3 db) means a 50 percent due to filter characteristics and pilot loss of power. Decibel is = 1/10 bel or tones. 0.1151 neper. It requires a known refe:cence Non-Synchronous - A non-synchronous level, and impedance. For example; db data set will accept any rate of input up usually in telephone work means dbm where to its designed limit and will deliver at o db is 1 milliwatt in 600 ohm. Another the same rate on output. common value is db6m where the reference Synchronous - Synchronous data sets will of 0 db is 6 milliwatts in 500 ohm. This accept only one specified rate of input and value is used principally in audio amplifier will deliver only at that rate on output. work where 500 ohm lines are used. Dbv is Type: used in measuring the open-circuit output of Analogue - Signals which may assume' devices such as microphones where the ref­ any amplitude for any period within a erence is 0 db = 1 volt with an infinite im­ generally restricted range and are of a pedance. Dba, decibels adjusted, this is continuous rather than pulsed nature. used as a base for noise measurements. It (Speech waves are analogue waves. ) references 85 dbm at 1000 cycles. Dba re­ Digital - Signals made up of pulses of places the obsoleted value dbrn. Some other discrete durations, amplitudes and per­ references which have been used are 10, iods. (Teletypewriter, etc.) 12.5 and 50 milliwatts with impedances of Transmission Mode: 52, 75, 100, 125, 150, 250, 300 ohm. Serial - Where each pulse is sent separ­ Therefore, unless the reference and impe­ ately, one after the other. The data dance are known, the term db is of little or speeds are usually referred to as bits per no value except to get an idea of the relative second. gain or loss in a circuit between points. Parallel - Where all the pulses comprising Decineper - 1/10 neper. a character are sent simultaneously or in

68 IBM CONFIDENTIAL Dedicated Service - See Leased Channel and Private Disconnect Signal - A signal transmitted from one Line. end of a subscriber line or trunk to indicate Delay Distortion - See Distortion, Delay. at the other end that the established connec­ Delay Equalizer - A corrective network which is de­ tion should be released. signed to make the phase delay or envelope Display Unit - Device which provides a visual repre­ delay of a circuit or system substantially sentation of data. constant over a desired frequency range. Distortion - Lack of similarity between a signal re­ See Equalizer. ceived over a transmission line and the sig­ Demarcation Strip - Usually refers to a terminal nal put on the line at the transmitting end. board acting as an interface between the Usually measured in percent. business machine and the common carrier. Amplitude - (Frequency - Harmonic) - Dis­ Demodulation - The process of retrieving an original tortion caused by unequal attenuation or signal from a modulated carrier wave. This amplification of different frequencies by technique is used to make communication a transmission line, filter, or other cir­ signals compatible with business machines cuit. signals. Bias - In teletypewriter applications, this is DFT - Diagnostic Function Test - A program to test defined as marks or spaces consistently over-all system reliability. too long or too short. If an alternate Dial Exchange - An exchange where all subscribers mark space test pattern were transmitted can originate their calls by dialing. with an equal amount of time between Dialing, Direct Distance - An exchange service transitions, the received signal will prob­ which enables a telephone user to select ably have a percentage of marking or subscribers outside the user's local area. spacing bias. This may be caused by the Dial Pulse - An interruption in the DC loop of a characteristics of the terminal, data set, calling telephone. It is produced by the or by an unequal rate of transmission. brealting and malting of the dial pulse con­ When the mark pulses appear lengthened, tacts of a calling telephone caused by the the space pulses will be shortened. This dialing of a digit. The loop current is inter­ condition is called MARKING or POSITIVE rupted as many times as the digit units Bias. When the mark pulses appear dialed. shortened, the space pulses will be Dial-Up - The service whereby a dial telephone can lengthened. This condition is called be used to initiate and effect a station-to­ SPACING or NEGATIVE Bias. station telephone call. Characteristic - The normal and predictable Dibit - A group of two binary bits; in 4-phase modu- distortion of data bits produced by char­ 1ation' each possible dibit is encoded as one acteristics of a given circuit at a parti­ of four unique carrier phase shifts. cular transmission speed. Digital Data - Information represented by a code Delay - (Envelope Delay, Phase Delay) - consisting of a series of bits. Distortion of a signal resulting from un­ Digital Subset - See Data Set. equal propagation time for different fre­ Direct Distance Dialing - DDD - Service which en­ quencies over a transmission line, ables the caller to dial toll calls without op­ through a filter, or other circuit. erator intervention. End - In start-stop teletypewriter signals, Director - A type of crossbar equipment used-to the shifting of the end of all marlting make cross-office selection and connection pulses from their proper positions in re­ from an input to an output in accordance with lation to the beginning of the start pulse. CDC's. (Telegraph applications.) A marlting end distortion denotes a Direct-Point Repeater - A telegraph operator in lengthening of the marlting bit. A spacing which the receiving relay controlled by the end distortion denotes a lengthening of signals received over a line repeats corres­ the spacing bit (mark bit shortened). ponding signals directly into another line or Fortuitous - A type of distortion which re­ lines without the interposition of any other sults in the signals being intermittently repeating or transmitting apparatus. shortened or lengthened. This distortion Disconnect (Release) - To disengage the apparatus is entirely random in nature and can be used in a telephone connection and to restore caused by battery fluctuations, hits on it to its condition when not in use. the line, power induction, etc. See Jitter.

IBM CONFIDENTIAL 69 Frequency - See Amplitude Distortion. Duplex - Term used to indicate that a channel or sys­ Harmonic - See Amplitude Distortion. tem can be used for communication in two Jitter - Peak Jitter - Random variation in bit directions. See Half Duplex and Full Duplex length due to noise, modulation process, definitions. etc. This results in a varying signal Duplex System - Having two distinct and separate duration caused by the non-constant machine facilities each of which is capable of switching time in the transition of a signal assuming the proceSSing function while the level. Jitter for the most part cannot be other assumes a standby.status. Usually, adjusted. It becomes more frequent at both systems are identical in nature. Duplex':" the higher rates of transmission. Also ing is utilized for greater reliablilty. mown as the combined effect of charac­ teristic and fortuitous distortion. Marking - See Bias Distortion. EAX - Electronic Automatic Exchange - A high Negative - See Bias Distortion. speed semi-automatic switching office now Positive - See Bias Distortion. undergOing development by General Tele­ Spacing - See Bias Distortion. phone. Teletypewriter Signal - In start-stop tele- Echo Check - A check which transmits received in­ typewriter signals, the shifting of the formation back to the source and compares transition points of the signal pulses from it with the original. their proper positions relative to the be­ Echo Suppressor - A line device used to prevent ginning of the start pulse. The magnitude energy being reflected back (echoed) to the of the distortion is expressed in percent transmitter. It attenuates the transmission of a perfect unit pulse length. See Bias, path in one direction while signals are being End, Fortuitous Distortion. passed in the other direction. Distributing Frame - A structure for terminating Effective Speed - Speed (less than rated) which can permanent wires of a central office, private be sustained over a significant period of time branch exchange, or private exchange and for and which reflects slowing effects of control permitting the easy change of connections be­ codes, timing codes, error detection, re­ tween them by means of cross-connecting transmission, tabbing, etc. wires. EIA Interface - A set of signal characteristics (time DLT - Data Loop Transceiver - Western Union's duration, voltage and current) specified by low-speed data set. the Electronic Industries Assn. for business Dot Cycles Per Second - One dot cycle is a mark machine/data set connections. and 'space. The speed of transmission of a Eight Level - A telegraph code which utilizes eight system in dot cycles per second is numeri­ impulses, in addition to the start and stop cally equal to half the speed of transmission impulses, for describing a character. expressed in bits per second or bauds. End Distortion - See Distortion, End. DR - Data Register. End Office - Class 5 office - local telephone ex­ Drop Relay - A relay actuated by a ringing current change where subscriber's loop terminates - and used to call on operator's attention to a See Exchange, Central. subscriber's line. End of Message - The specific set of characters Drop, Subscriber's - The line from a cable termin­ which indicates the termination of a message. ation to a subscriber's location. End to End Test - Dynamic test - a Bell System test Dry Contact - Term indicating a contact closure utilizing the 900 series test equipment. Re­ only. Used where one vendor controls by quires Bell maintenance personnel at each contact closure another vendor's voltage/ end of the circuit. current loop. Energy Level Diagram - A line drawing that shows Dry Reed Contact - Term usually used to differenti­ increases and decreases of electrical power ate from mercury wetted type. as current intensities rise and fall along a DS - Data Set. channel of signal communications. Dummy Load - A device in which the output power EOI - End of Idles. can be absorbed, used for simulating condi­ EOM - End of Message. tions of operation for test purposes. In EOT - End of Transmission. modem applications, a resistor, 8. 2K, which EOTR - End of Transmittal Record. may be substituted on the line for a modem. Equalization - The process of reducing frequency A dummy load counts as one modern. and/ or phase distortion of a circuit by the

70 IBM CONFIDENTIA L introduction of networks to compensate for Expander - A transducer which for a given amplitude the difference in attenuation and/or time de­ range of input voltages produces a larger lay at the various frequencies in the trans­ range of output voltages. One important type mission band. of expander employs the envelope of speech Equalizer - Any combination (usually adjustable) of signals to expand their volume. range. coils, capacitors, and/or resistors inserted Extension - 1. Additional telephone set on the same in transmission or amplifier circuit to im­ line but at a different location other than the prove its frequency response. main station. Equivalent 4-Wire System - A term applied to a 2. PBX station. carrier on repeater system using only one Extension, PBX, Outside - PBX station on premises pair of wires but different frequencies for separated from the PBX. Sometimes called each direction of transmission. Long Distance Locals. ERR - Error. Extension Station - A telephone station associated Error Rate - A measure of quality of circuit or with a main station through connection to the equipment; the number of erroneous bits or same subscriber line and having the same character in a sample, frequently taken per call number designation as the associated 100,000 char. main station. ESS - Electronic Switching System - Bell Systems External Clocking - This term is used by IBM to new electronic switching center utilizing identify the service where the data set (com­ high speed computers. mon carrier) supplies the time base oscilla­ Exchange - Exchange, Central Office - An office in a tor for the bit rate of transmission. See telephone system that provides service to the Data Set Clocking - the preferred term. general public where orders fo.r, or signals, controlling telephone connections are received and connections established. See End Office. Exchange Classes of - Facsimile (FAX) - A system for the transmission of Class 1 - See Regional Center fixed images. Type A facsimile is a system Class 2 - See Sectional Center of facsimile communication in which images Class 3 - See Primary Center are built up of lines or dots of constant in­ Class 4 - See Toll Center tensity. Type B facsimile (telephotography, Class 5 - See End Office photoradio, etc.) is a system of facsimile Exchange, Dial - An exchange where all subscribers communication in which images are built up originate their calls by dialing. of lines or dots of varying intensity. Exchange, Manual - An exchange where calls are Facsimile-Signal Level - An expression of the max­ completed by an operator. imum signal power or voltage created by the Exchange, Private Automatic (PAX) - A dial exchange scanning of the subject copy as measured at that provides private telephone service to an any point in a facsimile system. According organization and that does not allow calls to to whether the system employs positive or be transmitted to or from the public telephone negative modulation, this will correspond to network. picture white or black, respectively. It may Exchange, Private Automatic Branch (PABX) - A be expressed in decibels with respect to private automatic exchange that provides for some standard value such as 1 milliwatt or 1 the transmission of calls to and from the volt. public telephone network. Far-End Cross Talk - Cross talk which travels Exchange, Private Branch (PBX) - A manual or dial along the disturbed circuit in the direction in exchange, connected to the public telephone which the signals travel in that circuit. To network often located on a customer's prem­ determine the far-end cross talk between ises and operated by his employees. two pairs, 1 and 2, signals are transmitted Exchange, Service - A service permitting intercon­ on pair 1 at station A, and the cross talk nection of any two customers' telephones level is measured on pair 2 at station B. See through switching equipment. Near-End Cross Talk. Exchange, Toll - A toll office where customer's calls FCC - Federal Communications Commission - A are connected to toll circuits or toll circuits board of seven commissioners appointed by are interconnected. An exchange where toll the President under the Communications Act or long-distance connections are made. of 1934, having the power to regulate all Exchange, Trunk - An exchange primarily devoted to electrical communication systems originat­ handling trunk calls. ing in the United States.

IBM CONFIDENTIAL 71 FD or FDX - Full Duplex. Free Routing - That method of traffic handling FDM - Frequency Division Multiplex. wherein messages are forwarded toward Feed Holes - Holes punched in a tape to enable it to their destination over any available channel, be driven by a sprocket wheel. normally the most direct without depending Feed Pitch - The distance between the centers of on a predetermined routing doctrine. feed holes. Frequency Division Multiplex - See Multiplexing. Fieldata Code - A standardized military data trans­ Frequency Modulation - Variation of a carrier fre­ mission code, 7-data plus 1-parity bits. quency in accordance with an information Figure Shift - A control character in the Baudot signal. code after which characters are interpreted Frequency-Shift Keying (FSK) - Frequency-Shift as belonging to the grouping containing nu­ Transmission - A system of automatic code merics, punctu.ation and special symbols transmission and reception that shifts the (upper case). the carrier frequency back and forth between FINAC - A leased automatic teletypewriter system two distinct frequencies to designate mark provided by AT&T. and space, instead of keying the carrier on Five Level - A telegraph code which utilizes five and off •. impulses, in addition to the start and stop FTS - Federal Telecommunications System. impulses for describing a character. Full Duplex - See Channel, Full Duplex. Foreign Exchange Service - A service which con­ Full Speed - Referring to transmission of data in nects a customer's telephone to a telephone teleprinter systems at the full rated speed company central office normally not serving of the equipment. the customer's location (such as tie lines). Fully Perforated Tape - Perforated paper tape in Fortuitous Distortion - See Distortion, Fortuitous. which the perforations are complete. That Four-Row Keyboard - Used for origination of 8-level is, the punch makes a complete hole in the codes eliminating the need for figures/letters tape (as opposed to chadless tape where the case shifts. As opposed to three row. hole is not completely punched out). Four-Wire Circuit - See Channel, Four-Wire. Function Key - A term associated with specific keys Four-Wire, Half Duplex - IBM term only, does not on a teletypewriter (for example, "CR", refer to communication line services. "LF", "LTRS", "FIGS", etc.) which, when Four-Wire Repeater - Repeater which provides for operated, cause the teletypewriter to per­ transmission in opposite directions on two form mechanical functions so that a message transmission paths. may be received in proper form. Four-Wire Terminating Set - Hybrid arrangement by which 4-wire circuits are terminated on a 2-wire basis for interconnection with 2-wire circuits. GM - Group Mark. Fox Message - A standard mesflage which is usen Group - In telegraphic usage - a word. for testing telegraph circuits and machines Group Mark - Any indicator to signal the end of a because it includes all the alphanumerics as word or other unit of data. well as most of the function characters. Frame, Type A - Distributing frame carrying on one side (horizontal) all outside lines, and on the other side (vertical) the terminations of the Half Duplex - See Channel, Half Duplex. central office equipment and protective de­ Half Speed - Referring to transmission of data in vices for them. teleprinter systems at half the rated speed Frame, Type B (Main) - Distributing frame carry­ of the associated equipment. ing on one side (vertical) all outside lines and Hand Shaking - Exchange of predetermined codes protective devices for those lines and on the and signals when a connection is established other (horizontal) all connections of the out­ between two data terminals. side lines toward the central office equip­ Hard Copy - A machine printed document, such as ment. a message, order or invoice. Framing - The process of selecting the bit group­ Harmonic Distortion - See Distortion, Amplitude. ings representing one or more characters Harmonic Telephone Ringer - A telephone ringer from a continuous stream of bits. which responds only to alternating current Framing Bits - Non-information carrying bits used within a very narrow frequency band .. A to make possible the separation of characters number of such ringers, each responding to in a bit stream. a different frequency, are used in one type of selective ringing. 72 IBM CONFIDENTIAL HD or HDX - Half Duplex. Interface - A common boundary - for example, Header - The initial characters of a mes,sage desig­ physical connection between two systems or nating addressee, routing, time of origina­ two devices. tion, etc. Intermediate Distributing Frame (IDF) - A distribut­ Hits - Hit on the Line - Momentary line disturbances ing frame in a local central office, the pri­ which could result in mutilation of charac­ mary purpose of which is to cross-connect ters being transmitted. the subscriber line multiple to the subscriber Hollerith Code - The 12-unit code used in conven­ line circuit. In a private exchange, the in­ tional punched tabulating machine cards. termediate distributing frame is for similar Home Loop - Data path, allowing off-line use of purposes. terminal components. Internal Clocking - This term is used by IBM to HSSTR - High Speed Synchronous Transmitter Re­ identify the service where the business ma­ ceiver. chine supplies the time base oscillator for Hybrid Coil - Four-winding coil wound and connected the bit rate of transmission. See Non Data so that incoming and outgoing currents in a Set Clocldng - the preferred term. 2-wire path are separated and kept from in­ International Telecommunication Union (ITU) - A terfering with each other. civil international organization established to provide standardized communication proce­ dures and practices including frequency allo­ cation and radio regulations on a world-wide ICA - Industrial Communications Association. basis. Idles - Bit Code 1 8 R 0 set when no other trans­ Interoffice Trunk - A direct trunk between local cen­ mission is called for by the STR. tral offices in the same exchange. Incoming Trunk - Trunk coming into a central office. Interpreting - Printing the symbol or meaning of Indicator, Routing - A group of letters, engineered holes in the same paper tape or cards in and assigned to identity a station within a which they are punched. teletypewriter network. Intertoll Dialing - Dialing over intertoll trunks. Induction Coil - Coupling transformer. Intertoll Trunk - A trunk between toll switchboards Information Bit - One of those bits which are used to in different offices. specify the characters of a given code group Inverse Neutral Telegraph Transmission - That (opposed to framing bits). form of transmission in which marlting sig­ In-Line Processing - Processing in order of receipt, nals are zero current intervals and spacing without prior grouping or sorting, of transac­ signals are current pulses of either polarity. tions. In-Plant System - A system whose parts, including remote terminals, are all situated in one building or localized area. Jitter - See Distortion, Jitter. INQ - Inquiry. Joint Use - The simultaneous use of a pole, line, or Intercepting - Routing of a call placed to a discon­ plant. Facilities by two or more kinds of nected or nonexisting telephone number, to a utilities. operator or to a machine answering device. Junction Pole (S-Pole) - A pole at the end of a trans­ Intercepting, Operator - Answering an intercepted position section of an open-wire line or the call by an operator who asks, "What number pole common to two adjacent transposition did you call, please?" and is then given in­ sections. structions on completing the call. Intercepting Trunk - A trunk to which a call for a vacant number or changed number or a line out of order is connected fo:c action by an Key Click - Those components of telegraphic radia­ operator. tion that are set up as transients by the Intercommunicating System - A privately owned opening or closing of the signaling key but system without a switchboard capable of two­ are not essential for communication. way communication. It is normally a single Key-Click Filter - A filter that attenuates the surges unit, building or plant. Stations mayor may produced each time the keying circuit of a not be equipped for originating a call, but transmitter is opened or closed by the key. they can answer any call. Key Pulse - System of signaling where numbered Inter-Exchange Channel - Channel connecting two keys are depressed instead of using a dial. different metropolitan areas.

IBM CONFIDENTIAL 73 Keying - The forming of signals, such as those em­ Line, In-House - A privately owned or leased line ployed in telegraph transmission, by the that does not cross a public right of way. modulation of a direct current or other Line Level - The signal level in decibels at a partic­ carrier between discrete' values of some ular position on a transmission line. . characteristic. Line Loop - See Local Loop . Keying Chirps - Sounds accompanying code signals Line Loop Resistance - The metallic resistance of when the transmitter is unstable and shifts the line wires that extend from an individual slightly in frequency each time the sending telephone set to the dial central office. key is closed. Often called loop resistance. Keying Wave - The emission that takes place in Line Noise - Noise originating in a transmission telegraphic communication while the active line. portions of the code characters are being Line Printer - A printer in which all characters transmitted. Also called Marking Wave. across an entire line of type are printed in KSR - Keyboard Send/Receive - A teleprinter unit one printing cycle. with keyboard and printer. Line Relay - A relay which is controlled over a subscriber line or trunk line. Line Speed - The maximum rate at which signals may be transmitted over a given channel; Lag (In Telegraph System) - The time elapsing be­ usually in baud or bits/sec. tween the operation of the transmitting de­ Line Stretcher - An impedance matching device for vice and the response of the receiving device. coaxial transmission lines. Landline - A telegraph or telephone line passing Link - 1. In dial central offices, a complete talking over land, as opposed to submarine cables. path. LD - Long Distance. 2. Any combination of switches to accomplish LD Line - A telephone line or channel between two that path, such as a linefinder and connector central offices in different exchanges. tied together. LD Office - A central office primarily arranged for Link Group - Those links that employ the same terminating LD lines, switching trunks, re­ multiplex terminal equipments. cording trunks, and recording-completing Load - 1. A resistor or other impedance which can trunks and for their interconnection with each replace some circuit element temporarily or other. permanently removed. LD Switching Center - An LD office that serves as a 2. The power that a machine or apparatus switching point between local exchanges and delivers. the long distance telephone network. 3. The device used to absorb power and con­ LD Switching Trunk - A trunk extending from an LD vert it into the desired useful form. office to a local central office for connecting Load and Go - A computer operation and compiling LD lines to user lines. technique in which the pseudo language is Leased Channel - A point-to-point channel reserved directly converted to machine language and for sole use of a single leasing customer. the program run without an output machine - See Private Line Circuit. language program being created. Letters Shift - A control character in the Baudot Loaded Lines - (Loaded Cable) - A transmission line code after which all characters are inter­ or cable pair which has had inductance (load preted as belonging to the group containing coils) added in series with each conductor, letters (lower case). usually at definite spaced intervals. Common Level Compensator - An automatic gain control de­ load coil spacings are: vice used in the receiving equipment of a B 3000 feet telegraph circuit. D 4500 feet Line - See Circuit. H 6000 feet Line Adapter - See Data Set. M 9000 feet Linear Distortion - Amplitude ·distortion wherein Loaded cable pairs are usually designated by the output signal envelope is not proportional an alphanumeric code as follows: Two digits to the input signal envelope but no alien fre­ representing the wire gauge, a letter denot­ quencies are involved. ing the load coil spacing and two or three Line Hit - An electrical interference causing the digits representing the load coil inductance introduction of spurious signals on a circuit. in millihenries.

74 IBM CONFIDENTIAL For example: of a closed circuit or loop. LRC - Longitudinal Redundancy Check. 19 B 88 LTRS - "Letters" shift. . + , Lumped Loading - The action of inserting uniformly / Load Coil Load Coil In- spaced inductance coils along the line, as Wire Gauge Spacing ductance in opposed to continuous loading. See Loaded 1 millihenries Lines. \ / Main Distributing Frame (MDF) - A distributing 22 H 135 frame, on one part of which terminate the permanent outside lines entering the central Local Battery Talking-Common Battery Signal Tele­ office building and on another part of which phone Set - A local battery telephone set in terminate the subscriber line multiple cabl­ which current for signaling by the telephone ing, trunk multiple cabling, etc., used for station is supplied from a centralized direct­ associating any outside line with any desired current power source. terminal in such a multiple or with any other Local Channel - In private line service, the term outside line. It usually carries the central "local channel" refers to that portion of a office protective devices and functions as a complete circuit between the toll office (inter­ test point between line and office. In a pri­ exchange channel terminal) and the customer's vate exchange the main distributing frame is premises. See Local Loop. for similar purposes. Local Exchange - An exchange serving a compara­ Main Station - A telephone station with a distinct tively small group of customers, not exceed­ call number designation, directly connected ing 10, 000 in number; 10, 000 is the basic to a central office. unit of the A T&T switching" system. The Margin Control - See Range Finder. term is quite often used to refer to the build­ Mark - The presence of a bit or signal on the line. ing which houses the central office equip­ In telegraph applications it is an impulse ment used to provide the local exchange ser­ which, in a neutral circuit, causes the loop vice. to be closed; or in a polar circuit, causes Local Loop - A channel connecting the subscriber's the loop current to flow in a direction oppo­ equipment to the line terminating equipment site to that for a space impulse. in the central office exchange. Usually me­ Mark-Hold - The normal no-traffic line condition tallic circuit (either 2-wire or 4-wire). whereby a steady mark is transmitted. May Local Service Area - That area within which are be a customer selectable option. located the stations which a customer may Marking Bias - Bias distortion which lengthens the call at rates in accordance with the local marking impulse by advancing the space-to­ tariff. mark transition. See Distortion, Bias. Lock-Out - In a telephone circuit controlled by two Marking End Distortion - End distortion which voice-operated devices, the inability of one lengthens the marldng impulse by delaying or both subscribers to get through, either the mark-to-space transition. See Distor­ because of excessive local circuit noise or tion, End. continuous speech from either or both sub­ Marking Wave - In telegraphic communication, the scribers. emission which takes place while the active Long Line - A T&T term for circuits between ex­ portions of the code characters are being changes. transmitted. Also called Keying Wave. Loopback Test - A test, if available within the data Mark-to-Space Transition - The transition, or set, under control of a Bell data test center switching, from a marking impulse to a where signals are looped from the test center spacing impulse. Also may denote a type of through the data set and back to the test cen­ bias distortion. ter for measurement. Master Station - A terminal having selection control Loop Jack Switchboard - A patch panel with rows of of all other terminals on a multipoint circuit. vertical jacks. (Maximum capacity of 90 MBR - Memory Buffer Register. . channels). Each vertical jack strip consists Mercury Wetted Relay - Uses mercury as relay con­ of two looping jacks, a set jack, and a mis­ tact closure substance. cellaneous jack. Message - A sequence of words or symbols which is Loop Test - A method of testing employed to locate complete in itself; typically consists of head­ a fault in the insulation of a conductor when er, text and EO M. the conductor can be arranged to form part Message, Broadcast - A message sent to all termin­ als ona network. IBM CONFIDENTIAL 75 Message Circuit - A long distance telephone circuit code modulation systems wherein the in­ used in furnishing regular long distance or stantaneous amplitudes of several signals toll service to the general public. The term are sampled and codes corresponding to is used to differentiate these circuits from these amplitudes transmitted in turn, tele­ circuits used for private line service. metering schemes wherein meter readings Message, Multiple Address - A message to be de­ from many different locations are "read" livered to more than one destination. one at a time by a central recording device. Message, Single Address - A message to be delivered Time division multiplexing may be effected to only one destination. either of two ways: Message, Switching - A system'in which messages 1. Sequential Servicing - The input/output between stations are routed through a central Units are served in a fixed sequence. point having a storage media. Messages are The two examples of time sharing given stored and forwarded when the appropriate above are of this type. outgoing circuit becomes available. 2. Demand Servicing - The input/output Microwave - An electromagnetic wave in the super­ units are served on a demand basis. A high frequency radio spectrum ranging from dial telephone exchange uses this type of 1, 000 to 300, 000 megacycles per second. servicing. Th~ common switching equip­ Miscellaneous Intercept - The act of intercepting ment is connected to a subscriber's line single-address messages containing a non­ on demand, the demand being ,indicated valid CDC and/or the action of intercepting when the subscriber lifts the handset off multiple-address messages without a proper the "hook". multiple-address code. See Willful Intercept. B. Frequency Division Multiplexing - This Mod/Demod - Abbreviated form for modulating and method is generally applied in getting sev­ demodulating units. See Data Set. eral signals over one transmission line. Modem - Contraction of modulator - demodulator. rt is accomplished by having the various See Data Set. signals modulate different carrier fre­ Modulation - The process by which some character­ quencies using mixing and filtering techni­ istic of one wave is varied in accordance with ques. In this method all signals may be another wave. "ON" simultaneously. Examples - two or Multidrop-Multipoint - So named because several more IBM transceiver chanr..els on one line, terminals are connected to a single line. radio broadcasting, telephone carrier These terminals mayor may not have the systems. ability to communicate with each other. The Multipoint - Private line arrangement having more prime application for this circuit configura­ than two terminals connected by the same tion would be a low traffic circuit. A savings line. in line cost can be realized when using the Near-End Cross Talk - Cross talk which is propa­ multidrop configuration. gated in a disturbed channel in the direction Multiplexing - Multiplexing is any means whatsoever opposite to the direction of propagation of the whereby two or more signals (or the output current in the disturbing channel. The ter­ of two or more system elements) share the minal of the disturbed channel at which the same physical transmission facility, circuit near-end cross talk is present is ordinarily element or system component. Multiplexing near or coincides with the energized termi­ can be subdivided into two categories using nal of the disturbing channel. See Far-End. method as a criterion. N eper - A unit of the same nature as the decibel but A. Time Division Multiplexing or Time­ differing from it in magnitude. One neper is Sharing. This method can be applied to equivalent to 8.686 decibels. sharing of a transmission line or sharing Network - 1. Communication term: An organization of a centrally located computer by several of stations capable of intercommunication but input/output units or sharing of anyone not necessarily on the same channel. system component among several other 2. Engineering term: Two or more inter­ components. Time multiplexing is gener­ related circuits. ally accomplished by switching techniques. Network, Balancing - Lumped circuit elements (in­ In this method, the various signals or sys­ ductances, capacitances, and resistances) tem components take turns in having exclu­ connected so as to simulate the impedance of sive use of the transmission line or com­ a uniform cable or open -wire circuit over a mon system component. Examples - pulse band of frequencies.

76 IBM CONFIDENTIA L Network, Equalizing - Network connected to a trans­ the original recording functions and the ul­ mission circuit to correct, control, or alter timate data processing function. This in­ the response of the circuit in a desired way; cludes conversion operations as well as the particularly to equalize the response over a necessary loading and unloading operations frequency range. See Equalization. incident to the use of point-to-point or data­ Network, Leased Line or Private Wire - A series of gathering systems. In the telegraph sense, points interconnected by communications off-line means not in the loop. Paper tapes channels, and reserved for the exclusive use frequently are punched "off-line" and then of one customer. transmitted using a paper tape transmitter. Network, Private Telegraph - A series of points in­ On-Demand System - A system from which timely terconnected by telegraph or telephone chan­ information or service is available on request. nels and reserved for the exclusive use of One-Way Trunk - A trunk between central exchanges one customer. where traffic can originate on only one end. Network, Private Telephone - A series of points On-Hook - Unit de-activated (hung-up). interconnected by leased voice-grade tele­ On-Line - In the Teleprocessing Systems sense, an phone lines, with a customer operated ex­ on-line system eliminates the need for human change. intervention between source recording and the Neutral Circuit - A telegraph circuit in which cur­ ultimate processing by a computer. In the rent flows in only one direction. The circuit telegraph sense, it means in the loop. is closed during the marking condition and Open-Circuit Jack - A jack that normally leaves its open during the spacing condition. Also circuit open. The circuit can be closed only called Unipolar. through a circuit connected to the plug that is Noise - Random electrical signals introduced by inserted in the jack. circuit components or natural disturbances Open Wire - A conductor separately supported above which tend to degrade the performance of a the surface of the ground, and separately communications channel. supported on insulators. Noise Killer - An electric network inserted in a Open-Wire Line - A pole line whose conductors are telegraph circuit, usually at the sending end, principally in the form of open wire. for the purpose of reducing interference with OPM - Operations Per Minute - Equivalent to char­ other communication circuits. acters per minute when control functions are Nominal (Rated) Speed - Maximum speed or data rate included. of terminal which makes no allowance for nec­ Options - Usually refers to the strapping options essary delaying functions as checking, tab­ (features) available within data sets. These bing, etc. options are wired in during installation. Non Data Set Clocking - This term identifies the Some typical options are: service where the business machine supplies Originate - Data set always is in originate the time base oscillator for the bit rate of frequency mode. transmission. This is also referred to by Answer - Data set always is in answer IBM as Internal Clocking and by the common frequency mode. carrier as External Clocking. To avoid con­ Remote - Business machine controls the data fusion use Non Data Set Clocking or Data set's operation in either the originate or Set Clocking. answer frequency mode. Non Loaded Lines - (Non-Loaded Cable Pairs) - Mark Hold - Quiescent condition of the line is Cable pai rs or transmission lines with no is in a mark condition. added inductive loading. As opposed to Space Hold - Quiescent condition of the line is Loaded Lines. in a space condition. Non Simultaneous Transmission - A communication Orientation (Teletypewriter) - An adjustment of the device capable of transmitting on one pair of time the receiving apparatus starts selection, a Full Duplex Circuit, but not capable of with respect to the start signal. See Range receiving on the other pair at the same time. Finder. Out-of-Service Jack - Jack associated with a test jack which removes the circuit from service when a shorted plug is inserted. Off-Hook - Unit activated. Out-Plant System - A data transmission system Off-Line - In the Teleprocessing Systems sense, consisting of one or more centrally located off-line describes that kind of system in terminals and one or more terminals located which human operations are required between at some distance.

IBM CONFIDENTIAL 77 PABX - Private Automatic Branch Exchange. movement of the armature is governed by the Pad - Device which introduces transmission loss direction of current flow. into a circuit. It may be inserted to intro­ Poll - A flexible, systematic method, centrally con­ duce loss or to match impedances. trolled, for permitting stations on a multi­ Pad Switching - Transmission loss pad automatically point circuit to transmit without contending cut in and out of a toll circuit for different for the line. desired operating conditions. Polling - Orderly selection, one at a time, of multi­ Page Printer - A printer printing characters one at ple terminals to allow transmission of traffic. a time in page format. The action whereby the multiplexor or control Paper Tape Reader - A device which senses and station says effectively to the terminal, "Do translates the holes in perforated tape into you have anything for me?" internal form. Power Level (dbm) - The ratio of the power at that Parallel-By-Bit - or Parallel Transmission - point to some arbitrary amount of power System where the bits of each character chosen as a reference. This ratio is usually occur simultaneously. Implies as many lines expressed either in decibels referred to 1 or wires as there are bits in a character. milliwatt, abbreviated dbm, or in decibels Parity Check - Addition of non-information bits to referred to 1 watt, abbreviated dbw. See data, making the number of ones in a group­ Decibel. ing of bits either always even or always odd. Primary Center - A control center connecting toll This permits detection of bit groupings which centers together - a class 3 office. Can also contain single errors. It may be applied to serve as a toll center for its local end offices. characters, blocks, or any convenient bit Primary Jack - Terminate line conductors in a long grouping. lines testboard in one direction and central PAX - Private Automatic Exchange. office equipment in the other. PBX - Private Branch Exchange. Priority Indicators - Groups of characters which Peak Jitter - See Distortion, Jitter. indicate the relative urgency of a message. Perforated - A more suitable word to use in com­ Private Automatic Branch } See listing bination with paper tape than the word Exchange - P ABX under punched, e. g., perforated tape includes Private Automatic Exchange - PAX Exchange punched paper tape. Private Branch Exchange - PBX Perforator - A paper tape punch which is controlled Private Lme Circuit - A circuit assigned to one manually. It is used for punching tape off­ particular customer for his exclusive use. line. Tie line. PH - Phase. Private Line Service - Communication service used Phantom Circuit - A superimposed circuit derived exclusively by one particular customer. from two suitably arranged pairs of wires Also, the whole process of providing private called side circuits, with each pair of wires line circuits. being a circuit in itself and at the same time Processing, Batch - A method of processing in which acting as one conductor of the phantom circuit. a number of similar input items are accumu­ Phase Distortion - See Distortion, Delay. lated and grouped. Phase Modulation - Control of the phase, or timing, Processing, In-Line - A method of processing in of a carrier signal by an information signal. which individual input transactions are com­ Plant (As Used by Bell System) - The local facility pletely processed and all pertinent records of Bell System consisting of the switching are updated without previously having been equipment, local service department, and grouped. central office personnel. Pulse Modulation - Transmission of information by Plantman - See Plant. modulation of a pulsed, or intermittent, Point-to-Point Transmission - Transmission of data carrier; pulse width, count, phase, and/or directly between two points without the use of amplitude may be the varied characteristic. any intermediate terminal or computer. Polar Circuit - In telegraph applications a circuit in which current flows in one direction on a marking impulse and in the opposite direction Quad - A structural unit employed in cable, consist­ during a spacing impulse. Also called ing of four separately insulated conductors Bipolar. twisted together. Polar Relay - A relay containing a permanent magnet Quarter-Speed - Refers to transmission of data in that centers the armature. The direction of teleprinter systems at one fourth the rated

78 IBM CONFIDENTIAL speed of the associated equipment. of decibel units. For sound loudness, the Queue - 1. A waiting line generated by the time reference level is usually the threshold of required to move through channels, e. g. , hearing. For communication receivers, the traffic at a toll booth, a line at a ticket window. commonly used level is 60 microwatts. A 2. To arrange in or form a queue. common reference in electronics is 1 milli­ watt and power is stated as decibels above or below 1 milliwatt (dbm). See Decibel. Reference Noise - The magnitude of circuit noise that Rain Barrel Effect - Sound noted on an over compen­ will produce a circuit noise meter reading sated line. equal to that produced by 10 micromicro­ Range Finder - An adjustable mechanism on a tele­ watts of electric power at 1, 000 cycles per typewriter receiver which allows the receiver - second. distributor face to be moved through an arc Reference Volume - That magnitude of a complex corresponding to the length of a unit segment. electric wave,' such as that corresponding to It is adjusted normally for best results under speech or music, which gives a reading of operating line conditions. See Receiving zero vu on a standard volume indicator. The Margin. sensitivity of the volume indicator is adjusted Rate Center - A point of measurement from which so that reference volume or zero vu is read the telephone company bases its mileage when the instrument is connected across a rates. 600-ohm resistance to which there is delivered Rated Speed - See Nominal Speed. a powe-r of 1 milliwatt at 1,000 cycles per RCD - Record. second. RCL - Receive Control Leader. Regenerative Repeaters - See Repeaters, Regenera­ RDC - Receive Data Condition. tive. Real-Time Operation - Concurrent operations for Regional Center - A control center connecting sec­ data processing (computing) and physical tional centers together. Every pair of re­ processing in such a way that the results of gional centers in the United States has a the computing operations are available when­ direct circuit group between them. ever needed by the physical processing oper­ Relative Transmission Level - The ratio of the test­ ations, and vice versa. tone power at that point to the test-tone Receiving-End Cross Fire - The cross fire in a power at some point in the system chosen as telegraph channel introduced from one or a reference point. The ratio shall be ex­ more adjacent channels at the terminal end pressed in db. The transmission level at the remote from the transmitter. transmitting switchboard is frequently taken Receiving Margin - In telegraph applications, the as the zero level reference point. See Zero usable range over which the range finder may Transmission Level Reference Point. be adjusted. The normal range for a prop­ Relay Center - Synonymous with message switching erly adjusted machine is approximately 75 center. points on a 120 point scale. Sometimes re­ Repeaters - A combination of apparatus for the ferred to as range or operating range. reception and transmission of either l"";way Record - A group of related facts or fields of infor­ or 2-way communication signals and deliver­ mation treated as a unit. ing corresponding singals which are either Recording Trunk - A trunk from a local central amplified or reshaped or both. A repeater office or private branch exchange to a long for I-way communication is termed a "I-way distance office, which is used only for com­ repeater" and for 2-way communication munication between operators. impulses a "2-way repeater". Normally a Redundancy - In the transmission of information, repeater is part of an echo suppressor. redundancy is the fraction of the gross infor­ Some types of repeaters are: mation content of a message which can be Type 22 - Maximum 18 db gain: triode eliminated without loss of essential informa­ operating with all equalization and balanc­ tion. Numerically, it is one minus the ratio ing equipment included. of the net information content to the gross Type 44 - Maximum 42 db gain: similar information content, expressed in percent. to Type 22 but used on four-wire circuits. Redundancy Check - A check which uses extra bits. Type E - 8 to 10 db gain: a negative Reference Level - The level used as a starting point impedance repeater or converter which is when designating the value of an alternating line connected through a single, double­ quantity or a change in the quantity by means wound transformer.

IBM CONFIDENTIAL 79 Type V - Maximum 25 db gain: this is the NOTE: By extension, it is common practice most universal type of repeater in use. to designate by these terms the conductors It is independent of the hybrid filters, having similar functions or arrangements equalizers, and line equipment which are in circuits where plugs or jacks may not associated with the line. This permits be involved. complete interchangeability. . RM - Record Mark. Repeater, Regenerative - Also called "Regens". RO - Receive Only - A receive only page printer. Normally a repeater utiliz ed in telegraph ROPP - Receive Only Page Printer - A teleprinter applications. Its function is to retime and unit with prjnter only for stations which do repower (retransmit) the received signal not generate messages. impulses. These repeaters are speed and Rotor - Phonetic term for ROTR. code sensitive and are intended for use with ROTR - Receive Only Typing Reperforator - A paper standard telegraph codes. tape punch which also types the received Repeater, Single Line - A telegraph repeater utiliz­ character on the edge of the tape. ing a pair of cross-coupled polar relays Routing - The assignment of the communications which are inserted in series with a circuit path by which a message or telephone call to repower the signal. will reach its destination. Repeating Coil - A 1 to 1 ratio audio-frequency Routing, Alternate - Assignment of a secondary transformer for transferring energy from communications path to a destination when one electrical circuit to another and to permit, the primary path is unavailable. in wire communication work, the formation Routing, Indicator - An address, or group of char­ of simplex and phantom circuits. acters, in the header of a message defining Reperforator - A paper tape punch which is con­ the final circuit or terminal to which the trolled electrically. It is used for punching message has to be delivered. tape on-line. Reperforators, in some cases, Routing, Message - The function of selecting the may be used as perforators for manually route, or alternate route, if required, by punching tape, as well as for producing a which a message will proceed to its destination. tape from on-line traffic. Sometimes used in place of message switching. Reperforator/Transmitter - Trade names used by RPT - Repeat. AT&T to indicate a teletypewriter receiver - RS - Request to Send (to Data Set, elicits response transmitter consisting of a reperforator and of Clear to Send - CTS). a tape distributor, each of which is independ­ RT - Reperforator /Transmitter - An integrated unit ent of the other. It is used as a relaying consisting of paper tape punch and paper tape device and is especially suitable for trans­ reader for temporary storage of traffic for forming the incoming speed to a different retransmission. outgoing speed. RTL - Receive Transmit Leader. Retard Coil - Choke coil. RTTY - Radio telecommunications. A method of Reverse Battery Supervision - A form of supervision telegraph communication using a radio link. in which supervisory signals are furnished Running Open - In telegraph applications, a term from the terminating end of the originating used to describe a machine connected to an end by reversing the direction of current open line or a line without battery. A tele­ flow over the trunk. graph receiver under such a condition Ring - 1. A ring-shaped contacting part, usually appears to be running, as the type hammer placed immediately in back of the tip. continually strikes the type box but does not 2. The negative or battery side of a tele­ move across the page. phone line. Ringdown - Signaling methods used to operate receiver's ringer. Ringing - The production of an audible or visible SCL - Send Control Leader. signal at a station or switchboard by means SCR - Serial Clock Receive (data set interface). of an alternating or pulsating current. SCT - Serial Clock Transmit (data set interface). Ringing Tone - Tone sent to a caller to indicate that SCU - Station Control Unit. that called line is being signaled. SDC - Send Data Condition. Ring Side - That conductor of a circuit which is Sectional Center - A control center connecting pri­ associated with the ring of a plug or the ring mary centers together - a class 2 office. spring of a jack.

80 IBM CONFlDENTIA L Seizure - A term used in automatic (dial) telephony Side-Circuit Repeating Coil (Side-Circuit Repeat to indicate the establishment of an electrical Coil) - A repeating coil that functions simul­ connection through the operation of the first taneously as a transformer at a terminal of switch. a side circuit and as a device for superposing Selective Calling - A form of telegraph communica­ one side of a phantom circuit on that side tions system. One loop may include several .circuit. machines but, with selective calling, only Signal to Noise Ratio (SiN) - Relative power of sig­ the machine selected will respond. The nal to the noise in a channel. device that controls the individual machines Simplex Channel - See Channel, Simplex. in response to a selective call (CDC) is Simplex Circuit - A circuit derived from an existing called a stunt box. wire circuit by the use of center-tapped Selector - In automatic (dial) telephony, a switch repeating coil. This additional circuit must which in response to dial pulses, hunts for use another wire conductor or ground return and chooses an idle circuit to extend a call. to complete its path. Selector Permanent - A permanent condition in a Simplex Operation - 1. A communication system or selector caused by a short circuit in the network capable of transmitting or receiving calling line loop or by failure of the calling in one direction only. Not capable of being telephone user to operate the dial immedi­ reversed. ately after hearing dial tone. 2. (Obsolete) A method of Semiautomatic Switching - Transfer of traffic from operation in which communication, i. e. , incoming to outgoing circuits under operator transmit-receive operations, take place in control (usually push -button). one direction at a time. This meaning now Serial-By-Bit or Serial Transmis sion - Used to synonymous with Half Duplex. identify a system wherein the bits of a char­ Simultaneously - Occurring at substantially the same acter occur serially in time. Implies only a instant of time. To be meaningful, the min­ single transmission line. imum time interval to be considered must be Serialize - To change from parallel-by-bit to serial­ specified. by-bit. Simultaneous Transmission - A communication Service, Extended Area - An exchange service with­ device capable of transmitting control char­ out toll charges, which extends over an area acters or data on one pair of a Full Duplex where there is a community of interest in Circuit and receiving information on the return for a somewhat higher exchange ser­ other pair at the same time. vice rate. Singing - Unstable oscillations on the line. Service, Private Line (Wire) - See Private Line, Single-Office Exchange - An exchange served by a Service. single central office. Sideband - Frequency band above and below the Single Operation (Simplex Operation) - Operation of carrier frequency produced as a result of a telegraph system in only one direction at modulation. a time. Side Circuit - A circuit arranged for deriving a Single-Wire Line - A transmission line that utilizes phantom circuit. In 2-wire side circuits, the ground as one side of the circuit. the conductors of each side circuit are Slice - To remove those parts of a wave form lying placed in parallel to form a side of the outside two given amplitude limits on the phantom circuit. In 4-wire side circuits, same side of the zero axis. the lines of the two side circuits, which are Slicer - A circuit which effectively amplifies a por­ arranged for transmission in the same direc­ tion of the incoming pulses lying between tion, provide a I-way phantom channel for two closely spaced amplitude levels. transmission in that same direction; the two Smoothline - See Non-Loaded Lines. conductors of each line are placed in parallel SOTUS - In 8 1 D 1 systems, a station control device to provide a side for that phantom channel. located at each station on a multi-station Similarly the conductors of the other two line. It is the selecting device at each lines provide a phantom channel for trans­ station. mission in the opposite direction. Source Recording - The recording of data in punched Side-Circuit Loading Coil - A loading coil for intro­ cards, punched paper tape, magnetic tapes, ducing a desired amount of inductance in a etc. Once in this form, the data may be side circuit and minimum amount of induc­ transmitted, processed or reused without tance in the associated phantom circuit. rekeying.

IBM CONFIDENTIAL 81 SND - Send. rotation of a telephone call. The selectors Sneak Current - A leakage current that gets into are electromagnetically operated and contain telephone circuits from other circuits. It is a number of tiers of fixed contacts with each too weak to cause immediate damage, but tier arranged in a semicircle. A moving can produce harmful heating effects if al­ contact arm first rises to the height of the lowed to continue. desired tier, then swings around horizontally SNG - Sending. and stops over the required contact. Solid State - Utilizing transistors, diodes, and STL - Send Transmit Leader. pressure components only; excludes tubes, Stop Element - Stop Bit - The last element of a relays, and other electromechanical devices. character in asynchronous serial transmis­ Sounder - A telegraph receiving instrument in which sions, used to insure recognition of next an electromagnet attracts an armature each start element. In telegraph applications, it time a pulse arrives. The armature makes is 1. 42 times as long as the unit data bit. an audible sound as it hits against its stops Store and Forward - The interruption of data flow at the beginning and end of each current im­ from the originating terminal to the designated pulse, and the intervals between these sounds receiver by storing the information enroute, are translated from code into the received in physical media (punched card or tape, etc.) message by the operator. and forwarding it at a later time. See Switch­ Space - The absence of a bit or signal on the line. ing Message. In telegraph applications, it is an impulse, STR - Synchronous Transmitter Receiver - This is which in a neutral circuit, causes the loop the transmitted receiver section of the 1009, to open; or in a polar circuit, causes the 1013, 7702, Autodin and other medium speed loop current to flow in a direction opposite to IBM Teleprocessing equipment. that for a mark impulse. Stunt Box - A device used in telegraph terminals to Space-Hold - The normal no-traffic line condition perform nonreadout functions such as car­ whereby a steady space is transmitted. May riage return, line feed, ring singal bell, be a customer selectable option. answer CDC's and TSC's, etc. Spacing Bias - Bias distortion which lengthens the SUB RCD - Substitute Record (Replaces Characters spacing impulse by delaying the space-to­ of Bad Parity). mark transition. See Distortion, Bias. Subscriber's Loop - See Local Loop Spacing End Distortion - End distortion which Subset - 1. In communications, a subscriber set, lengthens the spacing impulse by advancing such as a telephone. the mark-to-space transition. See Distor­ 2. A modulation and demodulation device. tion, End. See Data Set. Space-to-Mark Transition - The transition, or Sub-Voice Grade - Denotes a communications channel switching, from a spacing impulse to a mark­ wider than telegraph but narrower than voice ing impulse. Also may denote a type of bias grade channels. Considered capable of trans­ distortion. mitting data at from 180 to 600 bits/second. SPX - Simplex. Superposed Circuit - An additional channel obtained Standard Test-Tone Power - 1 milliwatt (0 dbm) at from one or more circuits, normally pro­ 1,000 cps. vided for other channels, in such a manner Standby - Condition of equipment which will permit that all the chann~ls can be used simultane­ complete stable operation within a short ously without mutual interference. period of time. Superposed (Superimposed) Ringing - Party-line Start Element - The first element of a character in ringing in which a combination of alternating certain serial transmission, used to permit and direct currents is utilized, the direct synchronization. currents, of both polarities, being provided Start-Stop Transmission - Asynchronous signaling for selective ringing. utilizing a start bit preceding the character Supervisory Control - A system for the selective and a stop bit following the character for control and automatic indication of the oper­ synchronization purposes. ation of remotely located units by electrical Station Battery - The electrical power source for means, over a relatively small number of signaling in telegraphy. common transmission lines. Carrier cur­ Step-by-Step Automatic Telephone System - A switch­ rent channels on power line can be used for ing system characterized by the use of suc­ this purpose. cessive step-by-step selector switches Supervisory Relay - A relay which, during a call, is actuated by current impulses produced by controlled by the transmitter current supplied

82 IBM CONFIDENTIAL to a subscriber line to receive from the asso­ completing a long distance call. ciated station signals that control the actions Switch Room - That part of a central office building of operators or switching mechanisms. that houses switching mechanisms and asso­ Supervisory Signal - A signal for attracting the ciated apparatus. attention of an attendant to a duty. Switch Train - In telephone, a sequence of switches Suppressed Carrier Transmission - That method of through which connection must be made to communication in which the carrier frequency establish a circuit between a calling telephone is suppressed either partially or to the max­ and a called telephone. i~um degree possible. One or both of the Synchronize - To lock one element of a system into sidebands may be transmitted. step with another. Usually refers to locking Switch Hook - A switch on a telephone set, associ­ a receiver to a transmitter, or can refer to ated with the structure supporting the re­ locking data terminal equipment bit rate to ceiver or handset. It is operated by the data set frequency. removal or replacement of the receiver or Synchronous - Having a constant time interval be­ handset on the support. tween successive bits, characters or events. Switching Center - Location where incoming data Synchronous Transmission - Continuous bit-stream from one circuit is transferred to the proper transmission, with no start-of-character outgoing circuit. identification. Switching Center, Automatic Message - A location System - An over-all term used to describe com­ where an incoming message is automatically munication facilities from an engineering directed to one or more outgoing circuits aspect, including all the associated equip­ according to intelligence contained in the ment. message. Switching Center, Semi-Automatic Message - A location where an incoming message is displayed to an operator who directs the Tandem - Method of interconnecting central offices message to one or more outgoing circuits by trunks when the central offices do not according to information read from the have trunks directly to each other. message. Tandem Central Office - A central office primarily Switching Center, Torn Tape - A location where used as a switching point for traffic between operators tear off the incoming printed and other central offices. punched paper tape and transfer it manually Tandem Completing Trunk - A trunk, extending from to the proper outgoing circuit. a tandem office, used as part of a telephone Switching Central - An installation in a wire system connection between stations. where telephone or teletypewriter switch­ Tandem Office - A central office used exclusively boards are installed to interconnect tele­ for interconnection of other end offices with­ phone or teletypewriter circuits. in the same exchange and near-by exchanges. Switching, Circuit or Line - A switching technique Handles no direct connection to subscribers. where the connection is made between the A class 5 exchange. calling party and the called party, prior to Tandem Trunk - A trunk, extending from a central the start of a communication. office to a tandem office, used as part of a Switching, Message - The technique of receiving a telephone connection between stations. message, storing it until the proper outgoing Tape Chadless - A tape used in printing telegraphy/ circuit is available, and then retransmitting teletypewriter operation. The perforations it. are not completely severed from the tape, Switching Through - Extension of a calling line loop, thereby permitting the characters represent­ clear of attachments, through one switch to ing the perforations in the tape to be printed a succeeding switch of a switch train. Some­ on the same tape. times referred to as Cutting Through, or Tape Relay - A method of receiving and retransmit­ Cut-Through. ting messages in tape form. Switching-Through Relay - A control relay of a line­ Tariff - 1. The published rate for a particular ap­ finder, selector, connector, or other stepping proved commercial service of a common switch, which extends the loop 9f a calling carrier. telephone through to the succeeding switch in 2. A list of the specifications for a service. a switch train. Usually designated relay D. TD - Transmitter - Distributor - The device in a Switching Trunk (LD) - Trunk from a long distance telegraph terminal which makes and breaks office to a local exchange office used for the line in timed sequence. Modern usage of

IBM CONFIDENTIAL 83 the term refers to a paper tape transmitter. Telegraph Switching Systems - Some of the existing TEL - Request for coordinating communication be­ switching systems are: tween terminals. AT&T Telautograph - A writing telegraph instrument, in 81D1 Full Duplex which movement of a pen in the transmitting 83B2 Half Duplex apparatus varies the current in two circuits FINAC Full Duplex in such a way as to cause corresponding SCATS Semiautomatic System movement of a pen at the remote receiving Western Union instrument. Also called Telewriter. Plan 57 Full Duplex Telecommunication - Transmission or reception of Plan 111 Contention signals, writing, sounds, or intelligence of Plan 115 Half Duplex any nature, by wire, radio, visual or other Plan 117 Full Duplex electromagnetic systems. Often used inter­ Telegraph Transmission Speed - The rate at which changeably with Communication. signals are transmitted, and may be meas­ Telectrograph - A system of phototelegraphy in which ured by the equivalent number of dot-cycles the original subject copy is composed of lines per second or by the average number of on a metal base, prepared by photograph letters or words transmitted and received through a single screen of parallel lines. A per minute. metal stylUS moving over the plate makes NOTE: A given speed in dot-cycles per contact with the metal base only in regions second (often abbreviated to dots per second) corresponding to dark areas of the picture, may be converted to bauds by multiplying by so that current flows for dark portions. At 2. The baud is the unit of signaling trans­ the receiver, this current makes a colored mission speed recommended by the Inter­ mark by electrolytic action on paper moving national Consultative Committee on Tele­ synchronously. graph Communication. Where words per Telegraph - System of communication by coded sig­ minute are used as a measure of transmis­ nals. As used today, hand sending and ear sion speed, five letters and·a space per word receiving are usually implied. are assumed. Telegraph Channel - A channel suitable for the Telemeter - To transmit digital and/or analog data transmission of telegraph signals. by radio waves, e. g. , data can be teleme­ NOTE: Three basically different kinds of tered from a missile and recorded at a ground telegraph channels used in multichannel tele­ station. graph transmission are: Telephony - The transmission of speech current 1. One of a number of paths for simultaneous over wires, by means of which two persons transmission in the same frequency range can converse effectively over a distance. as in bridge duplex, differential duplex, Teleprinter - Trade name used by Western Union to and quadruplex telegraphy. refer to its telegraph terminal equipment. 2. One of a number of paths for simultaneous Teletype - Trademark of the Teletype Corporation. transmission in different frequency ranges, A system for transmitting messages over as in carrier telegraphy. some distance employing keyboard or paper 3. One of a number of paths for successive tape sending and printing receiving. transmission, as in multiplex printing Teletypewriter - Trade name used by AT&T to refer telegraphy. Combinations of these three to its telegraph terminal equipment. types may be used on the same circuit. Teletypewritcr Exchange Service (TWX) - A forn1 of Telegraph Circuit - The complete circuit over which teletypewriter service in which suitably signal currents flow between transmitting arranged teletypewriter stations are provided and receiving apparatus in a telegraph system: with lines to a central office where connections It sometimes consists of an overhead wire or can be established between any such stations cable and a return path through the ground. and any similar station (in the same city or Telegraph Equipment Abbreviations·- in other cities) under control of the subscriber - ASR Automatic Send and Receive provided by AT&T. KSR Keyboard Send and Receive Telewriter - See Telautograph. RO Receive Only Telex (TEX) - An automatic Teletype Exchange ROTR Receive Only Typing Reper­ Service provided by Western Union. forator Telpak - Telpak service makes available wide-band R/T Reperforator/Tran smitter communication channels of various sizes

84 IBM CONFIDENTIAL suitable for large-volume point-to-point the tip spring of a jack. transmission of data, voice, teletypewriter, NOTE: By extension, it is common practice facsimile, or other services for a flat rate to designate by these terms the conductors regardless of usage. Telpak can be used as having similar functions or arrangements in a single large channel or a group of smaller circuits where plugs or jacks may not be channels. For example, a Telpak "A" chan­ involved. nel may be divided into 12 voice-grade chan­ TL - Transmit Leader. nels. See Carrier System. Toll - 1. A charge made for a connection beyond an Terminal, Job Oriented - A terminal specially exchange boundary. designed to receive source data in an envi­ 2. By extension, any part of telephone plant, ronment associated with the job to be per­ circuits, or service for which toll charges formed, and capable of transmission to and are made. from the system of which it is a part. Toll Center - Toll Office - Toll Point - Basic toll Terminal Repeater - A repeater for use at the end switching entity. A central office where of a trunk or line. channels and toll message circuits terminate. Terminal Room - A room, associated with a central Usually this is one particular central office office, private branch exchange or private in a city; however, larger cities may have exchange, which contains distributing frames, several central offices where toll message relays, and similar apparatus except that circuits terminate. A class 4 office. mounted in the switchboard sections. Torn Tape Switching - Manual transfer of incoming Terminal Unit - Communication-channel equipment messages in the form of punched paper tape that can be used for either input or output. to outgoing circuits for retransmission to Terminated Line - A transmission line terminated their destination. See Switching Center, in a resistance equal to the characteristic Torn Tape. impedance of the line, so there is no reflec­ Touch-Tone Dialing - The use of keys or pushbuttons tion and no standing waves. instead of a rotary dial to generate a sequence Test Board - Switchboard equipped with apparatus of digits to establish a circuit connection. for making tests and for temporary inter­ TR - Transmit. connection and rearrangement of circuits. Traffic (Communication) - All transmitted and Test, Busy - Test to determine if circuits are received messages. available and may be taken for use. Train - Sequence of pieces of apparatus joined to- \ Test Desk - In exchange testing, a board with trunks gether to forward or complete a call. See to distributing frames and testing apparatus Switch Train. for testing users' lines, switching trunks, TRAN - Transmit. and cable pairs. Transceiver - A terminal which is capable of both Test Handset (Hand Test Set) - A handset used for transmitting and receiving traffic. test purposes in a central office or in the Translator - Devices used in cross-bar systems outside plant. It may contain in the handle which change information coded by one system other components in addition to the trans­ to equivalent information coded by .another ducer; for example, a dial, keys, capacitors, system. It may convert a multifrequency and resistors. dialing code to a cross-bar marker code, a Test Tone - Tone used in identifying circuits or for 3-digit area code to a special local code, or trouble location. an equipment number to a telephone number. Test-Tone Power, Standard - See Standard Test- Transmission - The electrical transfer of a signal, Tone Power. message, or other form of intelligence from TEX - See Telex. one location to another. Text - The information portion of a message. Transmission Level - The transmission level of the Three-Row Keyboard - Utilized for transmission of signal power at any point in a transmission 5-level codes and requiring figures/letters system is the ratio of the power of that point shifts. As opposed to four row. to the power at some point in the system Tie Line - A leased channel, usually voice-gr~de. chosen as a reference point. This ratio is Tie Trunk - A telephone line or channel directly usually expressed in decibels. The trans­ connecting two branch exchanges. mission level at the transmitting switchboard Tip - The tip of a plug is the contacting part at the is frequently taken as the zero level reference end of the plug. point. See Decibel. Tip Side (Tip Wire) - That conductor of a circuit Transmission Section (Communications) - One of two which is associated with the tip of a plug, or or more portions of a long message, each of

IBM CONFIDENTIAL 85 which is transmitted separately. All trans­ Unattended Operation - A data set option allowing a mission sections of the same complete mes­ data call to be automatically answered by the sage use the same date-time group'. receiving station. As opposed to attended Transition - The instance of switching from one operation. state (e. g. , positive voltage) to a second Unbalanced to Ground - When applied to a cable pair state (negative) in a serial transmission. , or two wire line it means that the impedance Translators - Code conversion devices which may to ground as measured from one side of the generate a character sequence in response line is not equal to the impedance to ground to a single character, e. g., $ = dlrs. as measured from the other side of the line. Transposition - Interchanging the position of open Unbalanced to ground in cable pairs can make wire conductors to reduce noise and inter­ the unbalanced pairs susceptible to noise and ference. cross talk and can cause the unbalanced pairs Transposition Section - A length of open-wire line to to cross talk to other pairs. which a fundamental transposition design or Unipolar - See Neutral Circuit. pattern is applied as a unit. User's Set - Apparatus located on the premises of a Transverse Cross Talk Coupling - Between a dis­ user of a communication or signaling service turbing and a disturbed circuit in any given and designed to function with other parts of a section, the vector summation of the direct system. couplings between adjacent short lengths of the two circuits, without dependence on inter­ mediate flow in other nearby circuits. Triplex System - A telegraph system in which two Validity Check - A check for accuracy of character messages in one direction and one message representation.

in the other direction can be sent simultane­ Variolosser I - A device whose loss can be controlled ously over a single circuit. by a voltage or current. Trouble, Ticket - In testboard work, a small form VOGAD - Voice-Operated Gain-Adjusting Device - for reporting any circuit condition that re­ A device somewhat similar to a compandor quires a testboardman' s attention. and used on some long radio systems. A Trouble, Unit (LD) - Weighting figure applied to voice-operated device which removes fluctu­ circuits or circuit to indicate their expected ation from input speech, and sends it out at a performance in a given period of time. constant level. No restoring device is needed Trunk - A channel connecting switching centers or at the receiving end. exchanges, as opposed to local loops. Voice-Frequency Carrier Telegraphy - That form of Trunk Group - Consists of those trunks between two carrier telegraphy in which the carrier cur­ pOints both of which are switching centers rents have frequencies such that the modulated and/or individual message distribution points, currents may be transmitted over a voice­ and which employ the same multiplex terminal frequency telephone channel. equipments. Voice-Frequency Telegraph System - A telegraph Trunk Hunting - A method of switching incoming system permitting use of up to 18 channels on calls to the next consecutive number if the a single circuit. A different audio frequency first called number is busy. generated by a tuning-fork-controlled vacuum­ TSC - Transmitter Start Code - Usually a two-letter tube oscillator is used for each channel, being call that is sent to an outlying telegraph ter­ keyed in the conventional manner. The var­ minal which automatically turns its. tape ious audio frequencies at the receiving end are transmitter on. separated by suitable filter circuits and fed TT - Transmit Trailer. to their respective receiving circuits. TTY - Teletypewriter equipment. Voice-Grade Channel - A channel which permits Turn Around Time - The actual time required to transmission of speech. reverse the direction of transmission of a Voice-Operated Device - A device used on a telephone haU-duplex channel, data set and terminal. circuit, the object of which is to permit the (Nominally 200 milliseconds.) presence or some quality of the telephone Two-Tone Keying - See Frequency Shift. currents to effect a desired control. This de­ Two-Wire - See Channel, Two Wire. vice is used in most echo suppressors. Two-Way Trunk - Traffic originating either end. VRC - Vertical Redundancy Check. TWX Service - See Teletypewriter Exchange Service.

86 IBM CONFIDENTIAL VU - Voice Units - The gross amplitude of an elec­ Miscellaneous Grouping trical speech or program wave is called its volume and is expressed in VU' s. The ref­ o - Phase. erence volume is usually 0 VU which is one 4W/HD - Four Wire Half Duplex - IBM term only. millivolt of steady sine wave into 600-ohm Does not refer to communication line serviees. resistive load. A good volume is usually L21A - Transmission Measuring Set. between -10 to -30 VUe Anything over 0 VU WE2B - Noise Measuring Set - A device for measur­ is definitely too loud; anything under -55 VU ing noise in telephone channels. It is speech is definitely too soft. Readings will depend related and employs weighted networks to on the meter's frequency response and cal­ simulate the action of the ear. ibration criteria. 901 Data Test Set - This is an interface adapter designed to make out-of-service installation and routine tests on all Bell System data sets to date. The 901 Data Test Set includes an WATS - See Wide-Area Telephone Service. "adapter" which also permits in-service Way Station - Western Union terminology for a monitoring and measuring of signals in the station on a multipoint circuit. interface between the data set and business Wide-Area Telephone Service (WATS) - This service machine. is arranged for subscribers who make many 902 Data Test Set - This is a portable test set de­ outgoing long distance calls to many points. signed primarily for the measurement of Monthly charges are based on the size of the peak distortion, and for the detection of trans­ area in which the calls are placed, not on the mission errors in serial data sets. The 902 number or length of calls. Under the WATS data set is intended to be connected to, and arrangement, the United States is divided in­ operated in conjunction with, the 903 Data to six zones. The subscriber is billed a flat Test Set (63-bit word generator). rate according to the zones to be called on a 903 Data Test Set - This is a self-contained, portable full time or measured time basis. This can signal generator used to simulate business be an advantageous arrangement for data machine outputs. It provides a 63-bit binary transmission. word suitable for testing binary serial-type Willful Intercept - The act of intercepting messages data sets. The 903 Data Test Set also gen­ intended for stations having equipment or erates alternating-mark space signals line trouble. See Miscellaneous Intercept. called a dot pattern. WM - Word Mark. Word - 1. In telegraph, six operations or characters Acknow ledgements (five characters plus one space). (Group is also used in place of word.) The following sources were utilized in preparing this 2. In computing, an ordered set of charac­ material: ters which is the normal unit in which infor­ Electrical Communications Systems Engineering mation may be stored, transmitted, or oper­ Definitions and Abbreviations. Department ated upon within a computer. of the Army Technical Manual, TMll-486-11. WPM - Words Per Minute - Generally six characters Department of the Army, Washington 25, (including space) per word. D. C., 18 January 1957. WRS - Working Reference System - An actual system "Glossary", Data Systems Design Vol, 1, No. 11, working under specified conditions and used November, 1964. Pages 4, 8. as a reference for other telephone systems. Holmes, James E. Communications Dictionary. New York. John F. Rider Publishers, Inc., a Division of Hayden Publishing Company, Inc., 1962. Zero Transmission Level Reference Point - An McKenzie, Alexander A. "New Era in Telephony: arbitrarily chosen point in a circuit to which Electronic Switching," Electronics, October all relative transmission levels are referred. 19, 1964, Pages 72-85. The transmission level at the transmitting Rexroad, William D. Teletypewriter Fundamental switchboard is frequently taken as the zero Handbook. West Concord, Massachusetts. transmission level reference point. See Computer Design Publishing Company, 1965. Relative Transmission Level. Miscellaneous IBM Publications.

IBM CONFIDENTIAL 87 ANSWERS TO REVIEW QUESTIONS Term

Blr------~ r------~B5 SESSION 1

(b) 1. 1941 with the IBM 040 and IBM 057 2. a. To provide rapid transfer of source data to processing location. b. To provide accurate, timely reports to management for decision making. c. To accomplish a and b with r.educed time, 3. Message Switching (through DPC-B), Circuit effort, and expense. Switching (direct) 3. Telephone, Telegraph 4. (a) Single drop 4. 60, 75, 100 5. 48, 60, 80 5. True 6. 21,600 6. 900 (30 per TI, 30 TI's per line) 30 x 30 = 900 7. IBM Start-Stop (Asynchronous), Synchronous, 7. (a) Reliable reservation control Parallel Data, Telegraph (b) Advance hotel reservations for passen­ gers 8. 2260 9. 7770 or 7772 (c) Advance car rental arrangements (d) Special meal' considerations, medical 10. conveniences, etc. 8. (a) Maintenance scheduling f--- 5 Miles ------l (b) Accurate crew time logging 2701 5/360 1-----11/0 2702 (c) Weather Information Control CPU Channel or 2703 (d) Accurate control of seats, arrivals, departures 9. No, only through the DPC. 10. Federal Communications Commission, State Public Utilities Commissions. 11. Use of IBM equipment for transmitting and receiving data at locations physically removed from each other utilizing Te~ephone, Telegraph and Radio SESSION 2 communication facilities.

1. (a) Purpose SESSION 3 (b) Number and size of messages (c) Priority of messages 1. parallel (d) Accuracy required and cost of system 2. serial 2. (a) 3. A signal which causes a terminal to change from a transmitter to a receiver or from a receiver Term to a transmitter. 4. Modulation is the method of. causing one sig­ nal to vary, depending upon the characteristics of another signal, for the purpose of conveying intelli­ gence. (In one case, in a form acceptable by the channel. ) 5. parallel 6. serial 7. modulated 8. demodulates, serial 9. parallel, 4 of 8, BCD 10. (a) Punched cards (b) Magnetic tape (c) Punched paper tape (d) Visual display

88 IBM CONFIDENTIA L (e) Printed copy b. To improve signal to noise ratio and com­ (f) Disk or drum file pensate for line loss 11. to provide a dividing line of responsibility 21. Echo suppressors. The time required from 12. Interface specifications publication from end of sending in one direction until transmission data set manufacturer may begin in the opposite direction. Reduces 13. serialization throughput due to idle line time. 14. de serialization 22. 1. Crosstalk by maintaining more uniform 15. For the purpose of checking validity by signal levels on line agreement of odd/even count of bits in message 2. Noise effects reduced character 23. great, little, compression 16. start of record 24. Distributed 17. inquiry 25. Compensators 18. acknowledgement 26. .001, 600 19. (a) Inquiry 27. Low noise, low or no echo problem, better (b) End of transmission or message frequency response, handle slightly higher data (c) Aclmowledgement rates with a lower error rate than ordinary lines. 28. Channel SESSION 4 29. Modulation, De-modulation

1. Channel, circuit, line 2. False SESSION 5 3. b, c, a 4. Telegraphic, Subvoice, Voice, Broadband 1. Queueing is the procedure of holding mes­ 5. Baudot, 5, start, stop sages in a programmed sequence ready to be for­ 6. Yes, one warded to another destination. No, . Zero 2. Message switching is store and forward Mark while circuit switching is initial routing control to 7. Asynchronous signaling requires th..:.t each addressee direct without intermediate receive and character be prefixed by a Start bit and followed by retransmit. a Stop bit while special clocking circuits make this 3. Contention wasteful use of time unnecessary by controlling be­ 4. Polling is direction for the terminal to send ginning and ending of characters based on a count. to the control station. Addressing is direction from 8. Serial bit transmission disassembles a char­ control station to terminal to receive messages. acter and sends it one bit at a time over one circuit, 5. The message itself while parallel-bit transmission requires one circuit 6. b. skip that terminal and proceed to process for each bit value and sends the entire character at the remainder of the Polling List. once. 7. False - Customer may establish sequence 9. Herzians - abbreviated Hz 8. False 10. 3,000 9. False - May vary to meet priority or peak­ 11. True load requirements 12. False, see Figure 14 for example. 10. False - Use intercept procedure to route to 13. Modulation is the process of causing one nearest active terminal signal to vary its form, dependent upon the charac­ 11. False - Sequence and Journal Control teristics of another signal. 12. False - Priority coding can alter Queue 14. To provide a buffer zone between channels to handling minimize the possibility of interference between 13. a. Flagging channels (crosstalk) b. Retention of priority addresses in main 15. a. Amplitude, b. Frequency (FSK or FSM), storage, c. Phase (PSK or PSM), specifically t,his is 2 phase c. Transmit prior to logging, 16. Federal Communications Commission d. Priority Queues 17. Bit rate (speed) 14. a. Source of error check information 18. a. Telegraphic, b. Subvoice, c. Voice b. Retrieval file if message gets lost grade, d. Subvoice 15. False - Must have proper access key. Ex­ 19. 2.2V P-P, 1.1V P-P, 0.87V P-P ample: Normally, production department should not 20. a. To regenerate distorted signals into good be able to have access to Payroll data quality signals

IBM CONFIDENTIAL 89 16. While terminals are being addressed or polled Shift Register sequentially samples each bit inter­ they are in control mode and such data is usually not val of the Receive Data Line to the TN while step­ stored. Usually begin accumulating LRC in text ping the previously sampled bits and no bits up mode and in storing or outputting data. through the register until the counter circuit informs the machine that adequate time has been allowed and SESSION 6 a complete character is in the register.

1. Serialize - Deserialize SESSION 7 2. Parallel, Serial 3. Serial, Parallel 1. Data Set 4. Off 2. Frequencies 5. Slightly after bit time 8 (delay Ion) 3. Mark 6. So last bit will be still on line while new 4. Phase character is being loaded (after T's are all reset at 5. Bit errors about 8.4 time) 6. + (Plus), - (negative) 7. BCD, 4 of 8 8. To allow time to place last bit of character SESSION 8 in Line Control before resetting register. 9. To make sure old character is cleared before 1. Bi-Polar a new one is loaded 2. Uni-Polar 10. Mark 3. Current 11. 8, parallel, tran slator 12. On SESSION 9 13. Counter Circuit reaches 8 14. 8 1. Provide communication circuits for public 15. Space, 4 use in accordance with prescribed schedules and 16. Zero, space, 4 rates. 17. Counter circuit at 8 2. Federal Communications Commission 18. SERDES holds character and permits each 3. State Public Utilities Commission bit to be sampled to the line while shift register 4. Tariffs moves character up through the registers while 5. Standardization, Coordination ·presenting the character one bit at a time to the line. 6. a. Wide Area Telephone Service, b. Sub- 19. SERDES through bit timer permits each scriber Teletypewriter Exchange storage element a definite period during which it 7. A subscriber teletypewriter service may be turned On or left Off under control of the 8. 12 condition existing on the Receive Data Line. The 9. facsimile

90 IBM CONFIDENTIAL INTRODUCTION TO TELEPROCESSING

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