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AUTOMATIC NUMBER IDENTIFICATION. IDENTIFICATION INFORMATION DIGITS (ANI.. 11) ...... 34 Section 3 - Switching Impacts ...... 35 EQUAL ACCESS END OFFICES (EAEO) ...... 35 TOLL SWITCHES FOR IXCs ...... 35 MULTIPLE LD NETWORKS ...... 35 LONG DISTANCE NETWORK TOPOGRAPHY ...... 35 SIGNALING CHANGES ...... 36 TOLL FREE NUMBERS ...... 36 ROUTING REQUIREMENTS ...... 36 AMA REQUIREMENTS...... 37 INTRALATA COMPETITION ...... 37 CANADIAN EQUAL ACCESS ...... 38 CUSTOM LOCAL AREA SIGNALING SERVICES (CLASS) ...... 38 CMRS INTERCONNECTION...... 38 Section 4 -Billing Impacts ...... 38 Section 5 - Non-tangible Consequences ...... 38 THE PRESENT - 1996 - 2004 ...... 39 Section 1 - Regulatory ...... 39 TELECOMMUNICATIONSACT OF 1996 (TA-96) ...... 39 TA-96 IMPACT ON THE KINGSBURY COMMITMENT ...... 40 Section 2 - Numbering Impacts ...... 40 CONTRACT NUMBERING ADMINISTRATION ...... 40 LOCAL NUMBER PORTABILITY ...... 41 LOCATION ROUTING NUMBER (LRN) ...... 41 THOUSANDS-BLOCK.. POOLING ...... 41 Section 3 - Switching Impacts ...... 42 MULTIPLE LOCAL NETWORKS...... 42 ROUTING REQUIREMENTS ...... 42 AMA REQUIREMENTS...... 42 Section 4 -Billing Impacts ...... 43 Section 5 - Non-tangible Consequences ...... 43 Section 6 - Growth Through Acquisition and Mergers ...... 43 ... Section 7 - Competition in All Levels ...... 43 THE FUTURE - BEYOND 2004 ...... 44 Section 1 - Numbering...... 44 Section 2 - Switching - VoIP ...... 44 Section 3 -Responsibility for Change ...... 45 Section 4 - End User Impacts ...... 45 CONCLUSIONS AND RECOMMENDATIONS...... 46 Section 1 - Conclusions ...... 48 THE REAL ISSUE ...... 48 THE CLASH ...... 49 CONSEQUENCES ...... 50 RECOMMENDED SURGERY ...... 51 Section 2 - The Answer ...... 52

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Appendix .Reference Tables and Figures ...... 53 TABLE 1: NANP ADMINISTRATIVE RESPONSIBILITIES ...... 53 TABLE 2: STRUCTURE OF THE ITU RECOMMENDATION E.164 NUMBER FIELDS:53 TABLE 3: COMMON WIRELINE CUSTOMER DIALED PREFIXES AND ACCESS CODES FOR ORIGINATING CALLS ...... 53 TABLE 4: PLAN ORIGINATING CALL TYPES AND CONVENTIONS ...... 54 TABLE 5: 11X CODES (Used in SXS offices) ...... 55 TABLE 6: N11 CODES ...... 55 TABLE 7: NO0 CODES ...... 55 TABLE 8: DUAL TONE MULTI-FREQUENCY SIGNALING ...... 55 TABLE 9: ADDITIONAL NUMBERING NEEDS OF CMRS SERVICE PROVIDERS ...... 56 FIGURE 1 NATIONAL TOLL DIALING PLAN ...... 57 FIGURE 2 EQUAL ACCESS TOLL DIALING PLAN (POST MFJ) ...... 58 FIGURE 3 TOLL AND LOCAL DIALING PLAN POST (TA 96) ...... 59 FIGURE 4 HYBRID INTERWORKING NETWORK ...... 60 Glossary of Terms ...... 61 Bibliography and Illustrations...... 63

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DEDICATION

Tom Brokaw defined them as “America’s Finest Generation”. They came home from fighting World War I1 and built the finest telephone network in the world. It is in their memory that I dedicate this document.

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About the Author Author’s Introduction

David Bench has t has been over 125 years since the spent over 38 years Iinvention of the telephone. The original in the telephone industry. telephone was a simple device that operated Prior to his employment on Direct Current (DC). The telephone has at Nortel Networks, he evolved and has become a normal way ,of worked for a long- life and an expected appliance in our homes, distance company, two large independent offices and even on our persons. Millions of holding companies, and a Bell Operating people have used the telephone without Company. While employed by Alltel, he thought or worry about its functions or its served as a consultant for Alltel Middle East reliability. It is the one appliance, in the and provided consulting services to Mobile home, that people never worried about. If it Telephone Systems of Kuwait. He also broke, or ceased to function, the phone taught Traffic Engineering for the United company fixed or replaced it. Most people States Independent Telephone Association lived their lives thinking that there is only (USITA) for three summers at Michigan one “phone company”. In the, late 1960s, State’University. He also served on the Ernestine, a character on Laugh In, indicated USlTA Traffic Engineering Committee. she was from “The Phone Company”. In the ’ movie, “The President’s Ahalyst, the While at Nortel Networks, David has been antagonist worked for TTC (The Telephone part of DMS1100 Systems Engineering, Company). In reality there were hundreds DMS-10 Product Marketing, US Standards of telephone companies. All of these Management and now, Strategic Standards. telephone companies completed calls to the rest of ‘the world through l&g distance . , David is an authority on the North American facilities designed and maintained by Numbering Plan and represents Nortel AT&T. In 1983, the U.S.’Federal Courts Networks on the Industry Numbering broke up AT&T. Multiple long distance Committee (INC) and serves as Nortel’s companies now were able to carry alternate representative on the U.S. FCC interconnecting telephone traffic. The advisory council, the North American consumer was turned loose into a Numbering Council (NANC). David also competitive service that they did not represents Nortel Networks with the understand. Two decades have passed since Canadian Steering Committee on the AT&T breakup. In 1996, the US. Numbering (CSCN). Congress passed the Telecommunications Act of 1996. The major purpose of this act David represents Nortel Networks at the was to promote competition for local Network Interconnection / Interoperability telephone services. Competitive local Forum. exchange carriers need telephone numbers and interconnection agreements in order to David holds a certification as a Master compete for communications consumers. Telephone Engineer with an endorsement in Traffic Engineering by the National Technology innovations, such as mobile and Association of Radio and packet switching, have also increased Telecommunications Engineers (NARTE) consumer choices. All of this has created chaos in the competition for resources of the

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PSTN. Overall management of the PSTN system was developed so that telephone has been lost. There is not even any users could call people over long distances. common standard or definition of what (For example, the first transcontinental constitutes the PSTN. telephone call did not occur until 1915) The early decades were full of local competition, The communications industry, as a whole, inventions and litigations. Phone companies has done a poor job of educating the were created and equipment manufacturers consumer on the overall operation and sprang up. Sears & Roebuck and importance of what we know as telephone Montgomery Ward catalogs listed entire service. Consumer groups are too busy telephone line equipment for “Farmer’s criticizing phone companies than to educate Lines”. Interconnection standards did not consumers. exist until interconnection between companies and “Farmer’s Lines” was In an attempt to explain the operation of the attempted. The creation of AT&T as an PSTN, some historical data has been overall carrier of inter-company telephone simplified and other sections are not traffic created the need for standards to be discussed. Many more sections of the Plan developed. Some of these standards took exist other than numbering and switching. decades of trial and error studies before they These sections include transmission, were codified. Human operators placed signaling, end user equipment and network interconnections, and long distance management. These are contained in connections. Methods for signaling each industry specifications. other were developed by mutual consent. Operators learned that the more For a complete history of the early years, it switchboards that were interconnected, the is suggested that one read “Telephone, The harder it was to hear a conversation. As Firsf Hundred Years” written by John telephone technology developed into Brooks and published by Harper & Row, automatic connecting, the standards became Publishers in 1976. more stringent. All of this took decades of work by scientists and engineers using slide Alexander Graham Bell is credited with the rules and pencils. AT&T recognized the invention of the telephone in 1876. fact that a telephone system would only be However, it was Theodore Vail that perfected when everyone was connected to invented the “Phone Company”. Mr. Vail the system. This was referred to as became President of AT&T in 1885 and set “Universal Service”. AT&T put together its vision for decades to come. That vision the Bell System. AT&T was a powerful was “one system, one policy, universal political company that controlled the service”.’ That vision has brought the PSTN development, deployment and the out of many disasters in its history. interconnection standards for telephone systems until the US. Department of Justice At the time of the invention of the broke up AT&T in 1983. Many telephone, Thomas Edison had not yet international standards are still based upon patented the electric light bulb. Many the early AT&T standards. decades passed before a cohesive telephone This document refers to the North American I“Telephone, The First Hundred Years” by John Numbering Plan (NANP) and the Brooks and published by Harper & Row, Publishers Nationwide Toll Dialing Plan. For overall in 1976.

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simplification, I will just refer to this as the for the access, then it becomes a Public Switched Telephone Network telephone/communications company. (PSTN) unless the reference is just to numbers or switching. A Web Search of Prior to the MFJ, the prime objective, of PSTN reveals several definitions of it. The phone companies, was to complete a call. most accurate is as follows: The MFJ, bolstered by the Telecommunications Act of 1996, changkd The public switched telephone network that purpose. The purpose is now to get paid (PSTN) is the concatenation of the world’s for providing services. public circuit-switched telephone networks. Originally a network of fixed-line analog The purpose of this document is to educate telephone systems, the PSTN is now almost its readers on the history and philosophy of entirely digital, and now includes mobile as the PSTN. This will enable the reader to well as fixed telephones.* understand the PSTN’s functionality and its benefits to the users of the system. The worldwide PSTN is largely governed by Hopefully, this will enable regulators, technical standards created by the ITU-T, providers and users to understand the need and bses E.163E.164 addresses (known for considering the whole network as a ’ more commonly as telephone numbers) for functioning tool of our society and not just addressing. piece parts of various corporate business plans. The NANP PSTN is the North American segment of the worldwide PSTN and was I sometimes feel that, in the not to distant created to be independent of the technology future, we will wake up one morning with that is used in its operation. no dial tone and there will be no one who can fix it. I hope the reading of this I define the NANP PSTN as any group of document will prevent or at least delay that networks that are used to complete public catastrophe. messages between a calling NANP number and a called NANP number Readers of this document may feel that it through network elements defined in supports the views of the present RBOCs industry Rating and Routing data bases. and AT&T. It is quite the opposite. It This includes those elements that are part reveres the memory of past employees of the of the PSTN Signaling Network. (for Bell System and the Independent Telephone example: The using of NANP numbers Companies prior to January 1, 1984. In my qualifies the element as being part of the opinion, the present RBOCs and AT&T PSTN) relate to their predecessors in name only.

In my opinion, once Internet Service The opinions, conclusions and Providers complete traffic by accessing recommendations contained in this elements of the PSTN, they become a pari of document are mine. They are in no way the PSTN. If a company advertises that it is associated with my current employer, past a new type of telephone company, advertises employers or other industry affiliations. that it will complete calls using NANP numbers and interconnects with the PSTN

http://en.wikipedia.org/wikiIPSTN

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I EXECUTIVE SUMMARY elements function. The plan established the format and values of telephone numbers he North American Numbering Plan used in the 19 nations that are associated T(NANP)3 is the North American portion with the plan. This plan established a fixed of the worldwide Public Switched 10 digit format for NANP numbers. Just Telephone Network. It was developed, having a ten digit telephone number does coordinated and managed by AT&T from its not assure one of being able’ to make ,‘or inception in 1947 until the breakup of receive telephone calls. Calls must be AT&T (MFJ) on January 1, 1984. It was routed and properly billed by a then coordinated by Bell Communications comprehensive uniform method for rating Research Corporation (Bellcore), on behalf and routing of the messages developed by of the Regional Bell Operating Companies the plan. Calls are routed and rated based (RBOC), from 1984 until the enactment of upon the first six digits of a ten digit the Telecommunications Act of 1996 (TA- telephone number. The plan is totally 96). Since that time, it has not been independent af the technology that uses it. managed or even coordinated by anyone. The plan has evolved from manual The result of this government opening of the connections to electro-mechanical switching PSTN is that it is no longer managed. It has to stored program controlled analog ’ gone from a seamless network with one goal switching to stored program’ controlled to a hodgepodge of networks constructed by digital switching and now to packet individual business plans. In the name of switching. It has included CMRS competition, it has created multiple technologies from Mobil Telephone Service segments of service providers each trying to (MTS) to Cellular to Personal interconnect with each other and yet manage Communications Systems (pcsj to cut operating expenses. Each service provider segment has different perspectives CMRS systems are only wireless from the on network operation and has different customer instrument to the first tower site. regulatory rules for their operation. After that, they must connect and switch through the wireline network. The FCC has extracted the numbering portion of the NANP and hired an The real problem is the fact that the PSTN independent contractor to administer the still routes and rates messages exactly the numbers without regard to the management way It was envisioned in the 1940s. The of the network needed to switch the administration, handling and routing of numbers. telephone numbers is in at least five different data bases that do not communicate Telephone numbering resources are the with each other. “source code” by which the plan’s switching The deployment and growth of the Internet 3 The NANP is the basic numbering scheme for the has proponents promoting its use for voice telecommunications networks located in Anguilla, traffic. This is called Voice over Internet Antigua, Bahamas, Barbados, British Virgin Islands, Protocol (VoIP). Legislators and regulators Canada, Cayman Islands, Dominica, Dominican have been asked whether this service should Republic, Grenada, Jamaica, Montserrat, Si. Kilts & Nevis, Si. Lucia, St. Vincent, Turks & Caicos be regulated or not. Sides have been drawn. Islands, Trinidad & Tobago, and the United States There is a big difference between talking (including Puerto Rico, the US.Virgin Islands,

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I over the Internet and talking over an IP End users and government officials$expect mediated network. The use of the Internet their communications systems to handle for voice traffic still needs PSTN high speed expected traffic volumes and function in access and NANP telephone numbers to co- times of emergencies. exist. End users must have electrical service in order to be able to call over the Internet. On the cover sheet of this document, I asked Once the Internet is used for public voice who was managing the PSTN. *The answer, messages, it becomes part of the PSTN. It to that question, is that nobody is managifig needs co-existence methods to enable the the PSTN. new technology to be deployed and be a virtual seamless network.

The following are some issues involved with deploying VoIP for use in telecommunications:

e Lack of a common cohesive network Plan e Lack of defined Quality of Service ,* Lack of a common goal by service providers 0 Lack of a common plan for co- existence with the circuit switched PSTN

The dedovment-< of wireline telecommunications has had significant impact on people’s ability to receive help and receive notifications for events associated with public safety and civil defense. The PSTN was constructed and maintained for reliability and survivability. Today, the Internet has limited capabilities for this. It is a commercial venture. Regulators, providers and users need to understand and consider the whole network as a functioning tool of our society and not just piece parts of various corporate business plans.

End users of telephone services want to reach the person they called. They do not care what technology is deployed between them and the party they arc calling.

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THE PAST - THE BEGINNING Operators notified community leaders. This TO 1983 was one of the uses of operator to operator calling. (As an example, when World War I Section 1 - Telecommunications and ended, this information was sent out via Public Safety I Civil Defense chief operator notification. The Chief Operator then notified public officials and he deployment of telecommunications the local news media.). Thas had significant impact on people’s ability to receive help and receive Dial switching equipment contained notifications for events associated with equipment that could limit calling to only public safety and civil defense. One of the key people in the event of an emergency. reasons farmers deployed telephone lines, This was done to protect the network from even before they had electricity, was to get overload so that civil defense and help in emergencies. Early community emergency personnel could react to the telephone operators knew who to contact event. and where that person was in order to respond to an emergency. Early telephone Before hand held radios, large metropolitan operators let regular calls wait in order that telephone companies provided and the emergency was responded to, quickly. maintained “Police” call boxes that Bell System operator training instructed connected a police officer to the central operators on how emergencies were to be police station for check in and dispatches. handled. These procedures were important This equipment functioned on a ring down enough to be placed “under the glass” basis and messages were carried separate immediately in front of an operator. Before from the switched network in order to the late 1960s, children were instructed to maintain the reliability and survivability of call the operator in the event of an the system. emergency. An operator with an emergency stood up and was immediately joined by a Rural telephone companies provided group chief operator who plugged into the equipment and access to alert volunteer fire call to monitor and assist in the emergency. departments for deployment in the event of Operators spent hours locating family local emergencies. These systems rang the members to make notifications in the event phones in a number of fire official’s homes, of an emergency. Telephone operators when the fire reporting number was called. stayed at their positions during all sorts of Buttons placed on phones in the homes of disasters in order to handle emergency fire officials set off the local fire siren to requests. Deployment of government alert other volunteers. Some local telephone operated 9-1-1 Emergency centers has companies actually had their operators relieved telephone companies from the handle emergency calls and dispatch police, responsibilities of handling such calls. fire and ambulance units. CMRS Carriers and many Competitive Local Exchange Carriers do not even Telephone company operators routinely provide operator services. connected police officer’s calls to the police department from coin operated telephones. In the early years, the Bell System disseminated vital information by calling the Telephone equipment manufacturers built Chief Operators. In turn, the Chief specific products for fire and police

Version I .W Page I3 of 63 February 2004 UNDERSTANDING THE PUBLIC SWITCHED TELEPHONE NETWORK department's emergency communications Communications Assistance id, Law needs. This equipment was installed and Enforcement Act (CALEA). maintained by the local teleDhone comDany. Early The wireline telephone network ,serves as a systems backup and a fall back technology when dcplnyed a other systems fail, batteries lose power or rclegraph when emergency situations arise. CMRS \"

Today's stored program controlled Personal communications systems, such as switching systems have the ability to give CMRS, have extended a person's access to priority to certain emergency traffic such as emergency services. These systems also 9-1-1 calls. These switching systems can connect to public safety agencies using the also shed normal traffic to prevent system wireline network through interconnection. overloads. Section 2 - Regulation and Perspective The U.S. Federal Government has procedures that utilize the PSTN in SYSTEM REGULATION emergencies or failures in their fter the expiration of the Bell patents, communications systems. This capability is A AT&T recognized that competition for called the Government Emergency telephone customers was not in their best Telecommunications System (GETS). interest. AT&T worked with various federal Telephone systems are equipped to give and state governments to establish itself as a priority treatment to GETS calls. monopolistic regulated utility.

It was AT&T that suggested that 9-1-1 be The underlying principle, for this endeavor, used as a nationwide access to emergency was that the investment required to provide services. President Lyndon Johnson telephone service was a natural monopoly endorsed this proposal in 1968 and Bell and it wasn't in the public's interest to have Telephone companies immediately multiple providers tie up that much appointed 9-1-1 coordinators in each resources in attempting to provide service on engineering organization. The present a competitive basis. wireline and CMRS service providers have spent millions to give their customers access In order to have a monopoly that guaranteed to emergency enhanced 9-1-1 public safety it income levels, the Bell System established answering points (PSAP). They have also guidelines that regulators could monitor to complied with the requirements of the assure the end user of good service. As part of this service package, the telephone

Verrion I 00 Page 14 of 63 Februaly 2004 UNDERSTANDING THE PUBLIC SWITCHED TELEPHONE NETWORK company controlled and owned the entire two jurisdictions are regulated by State network including all terminal attachments Public Utilities Commissions. The FCC to that network. This ownership of all regulates the third jurisdiction. All revenues equipment was defined as real property. and expenses were categorized by these Each part had an assessed valuation and three jurisdictions. property taxes were paid to local governments for this real property. As a This guaranteed rate of return made AT&T result, the phone company was the largest or stock a safe investment. Many people’s life second largest tax payer in every savings and pension plans were invested in community. The other largest taxpayer was AT&T stock. The guarantee also enabled usually the power company. This method of telephone companies to concentrate on good local taxation still exists for incumbent service and service innovation. It enabled telephone companies. AT&T to grow through innovation and modernization. Regulations allow state regulators to franchise telephone companies and review WIRELINE HISTORICAL the quality of service provided by these PERSPECTIVE companies. Franchises can be revoked by he following historical perspectives states if service quality diminishes. Tapply to the wireline telephone industry Equipment and operating expenses use of telephone numbers since CMRS and associated with this service guarantee were other users did not exist at the time the figured into the equation that established PSTN was developed and implemented. telephone charges. Telephone numbers became necessary as In 1934, the U.S. Congress passed the soon as the first telephone operator could no Telecommunications Act of 1934. This Act longer remember what switchboard jack was created the Federal Communications assigned to the end user. The numbers Commission (FCC). The FCC created the initially were the manual switchboard panel Uniform System of Accounts so that utility and jack strip number assigned to the end finances could be reviewed in a standard user. Telephone numbers were only used format. for wireline telephone calls until Improved Mobile Telephone Service (IMTS) was There were three basic jurisdictions of calls initiated in the early 1950s. The numbering in the United States. plan was originated as the Nationwide Operator Toll Dialing Plan. It was changed 1.) Local area calls to the Nationwide Toll Dialing Plan. Later, 2.) Intra-State calls this became the North American Numbering 3.) Inter-State calls Plan (NANP). The development of the PSTN took many years and the Plan that Telephone equipment costs were categorized was chosen placed a three digit area code in for each of these jurisdictions in order to front of existing seven digit local numbers. determine charge rates, taxes and revenue The Plan was established before mobile divisions. telephone service. The Plan was finalized by AT&T on October 22, 1947 and later, These definitions are important for the shared with the independent telephone proper routing and billing of calls. The first companies through the United States

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Independent Telephone Association Section 3 -Numbering (USITA). The Plan was developed to automatically route and bill telephone NANP FORMAT AND VALUES: calls placed by long distance telephone lmon Strowger patented the dial operators. Atelephone in 1891. Prior to the deployment of dial switching, numbers were The Plan provided sufficient numbering verbally passed between callers and resources to carry the telephone industry operators and then between operators. into the 21” century. Every telephone, in the Between 1891 and the development of the numbering plan area, has had a unique 10 PSTN, local dialing could be anything from digit number associated with it since that two to seven digits. This was dependent time. upon the size of the community, the size of the local calling area and the capabilities of The NANP was developed in conjunction the switching system(s) being used. As with a nationwide switching plan. The communities grew, and the amount of two plans are complimentary to each telephones grew, digits were added in order other. Switching is based upon the to complete calls. number resources and the number routing is based upon the switching plan. By the 193Os, most large metropolitan areas were able to dial their own calls. Local For the most part, the numbering plan and service standards had been developed for the switching plan preserved state quality of service. However, there was no boundaries and assured state regulation of uniform dialing plan for the entire US. the service within the states. Investment and Telephone operators accessed other expenses can then be categorized by operators in distant cities and then asked to intrastate or interstate for rate purposes. be completed to a local number in that city.

The Plan was only utilized by toll operators AT&T developed a plan to allow calls to be (Operator Toll Dialing) until 1951, when, on dialed across the entire US. and Canada. November 10, 1951, Englewood, NJ became This plan took almost a decade and a half to the first community to access Direct design and implement. Its implementation Distance Dialing (DDD). The conversions was delayed by World War 11. AT&T to DDD were completed to the majority of settled on a ten digit plan. AT&T began areas within the US and Canada by the mid implementation of the plan in 1947. The 1960s. most notable part of the plan (to end users) was the development of a Nationwide This wireline perspective is important to Numbering Plan. understand as the application of the PSTN to other than wireline industry segments gets The numbering plan used in the United convoluted due to technical needs, States, and the other 18 nations served by architectural differences and regulatory Country Code 1, is known as the North differences for these industry segments. The American Numbering Plan (NANP). It is problems associated with other than wireline based on a “destination code” principle service provider applications of numbering where each main telephone (access line) in will be covered later in this document. the NANP has a specific “address” or “destination code” assigned to it. The

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I address is a ten digit number that consists of AT&T published a standard exchange name the following two basic parts: document in 1955 to eliminate these duplications6. This caused some exchange 1) A 3-digit Numbering Plan Area names to be changed. (NPA) code, commonly called the area code The four digit station number was chosen to accommodate some existing manbal 2) A 7-digit directory number operator systems and certain switching that is further divided into two equipment, called Terminal per Line (TPL). parts. TPL equipment needed 1000 numbers for every 100 lines. This equipment then (a) A 3-digit central office allowed up to ten telephones per line. The (CO) code. The term last digit of a phone number served by TPL central office, or CO, code equipment indicated the party position on a is used in this document party line. That was important,because the because of its long switching equipment needed that to standing use. In this determine the proper ringing scheme for that application CO means the particular telephone. Customers served by servicing end office that TPL equipment usually had to change their ’ provides dial tone to the number when they were lucky enough to get subscriber. a private line. TPL switching equipment was still deployed in the PSTN well into the (b) A 4-digit station number? 1980s. Modern stored program controlled switches can still handle up to eight parties In the initial definition, the first two digits of on a single line. the CO Code were defined by the first two letters of the exchange name (i.e. Some regulatory and industry documents BEachwood 4-578g5). Exchange names erroneously define telephone numbers and were associated with geographic line numbers as being synonymous. Line communities and letters were (still are) numbers are associated with the physical printed on telephone dials (the 1 or 0 dial line equipment that connects a wireline positions or keys do not contain letters). customer to a wireline switch. Most stored The exchange names were carryovers from program controlled switching systems can the manual switchboard days. This was associate multiple numbers with a single known as 2-5 Numbering. This stood for 2 line. They can also associate multiple lines letters and 5 numbers. After the to a single number. implementation of DDD, some exchange names produced duplicate two letter Therefore, a NANP telephone number is a designations with other exchange names. ten digit number that contains two 3-digit codes and a 4-digit station number. All ‘This section is taken from Notes on the BOC Intra- other numbers, used by telephone systems, LATA Networks, version TR-NPL-000275, Issue 1, fall in the category of prejixes or access April 1986. This was the Bellcore document that codes. The writien and printed succeeded the AT&T Notes on the Network and representaiion of a NANP number should be AT&T Notes on Distance Dialing. These AT&T documents are sometimes referred to as the “Blue Book”. 6 Bell System (AT&T) “Notes on Distance Dialing” 5 The Marvelettes, 1962, Tamia Records 1955

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NXX-NXX-XXXX. This will prevent exchange name. (ex. confusion with any other communications BEachwood 4 was BE 4) system that utilizes a numbering scheme. 1975 NANP Format and The values of NANP telephone numbers are -= N (0 or 1) X - the decimal digits 0 through 9. Initially, NXX - XXXX these numbers were generated by the opening and closing of a relay in dial pulse 1994 NANP Format and telephones. This pulsing was controlled by Values = NXX - NXX - springs and cams that regulated the speed of xxxx the telephone’s dial. The industry standard is ten pulses per second. In 1958, Bell The values Y and 2 have been used by Laboratories developed Dual Tone Multi- various authors when referring to a range of frequency (DTMF) tones to generate suggested values for a particular NANP numbers and to speed up connections. This proposal. Y and 2 are only used in their became known as “touch tone”’ The algebraic representation and were not used characters # and * were added to push in any official definition of a NANP button phones. Four additional tone pairs Number. were also defined with this signaling plan. Military uses of DTMF contained these four The format of the NANP is sometimes additional pairs. The DTMF frequencies written as ABC-DEF-GHIJ to facilitate and uses are in TABLE 8 in the Appendix. discussion of any particular value within the The additional characters, created with this format plan, now serve as network control characters. The dial equivalent to the * is PREFIXES AND ACCESS CODES: the digits 11. There is no dial equivalent to be industry has always employed the # character. Tprefixes and access codes to access certain capabilities or call types. The most EVOLUTION OF NANP FORMAT: common prefixes are the digit 1 preceding a 1947 Original NANP sent paid toll call and the digit 0 which Format and Values = N (0 precedes an operator handled toll call. or 1)’ X - NNX - XXXX These prefixes have evolved over time. (In where N = digits 2 through fact, the first exchange to access Direct 9 and X = any digit of 0 Distance Dialing (DDD) did not have to dial through 9. The NNX any access code. New York City did not portion of this plan have to dial any access code for long consisted of 2-letters and 1- distance until it was assigned its second number. The 2-letters were Area Code. Another early prefix, for long the first 2-letters of the distance calls, was 112 (see TABLE 5 for 11X Codes). (The prefix 112 was chosen because it was the access code for the “Long Distance Operator”.) The current list of ’ Touch Tone is a registered Trade Mark of Lucent commonly used wireline prefixes and access Technologies. Other names for this service include Digitone, Keycall, Tone Dial, Touch Button, etc. codes is contained in TABLE 3 in the * The use of the parenthesis in this instance indicates Appendix. Prefixes are usually deleted or that the central digit of the Area Code could only be a used in the originating switch before the 1 oraO. version I .w Page I8 of 63 February 2W UNDERSTANDING THE PUBLIC SWITCHED TELEPHONE NETWORK

6 called digits are forwarded. This was not OTHER CODES: Special always the case in some rural areas. n addition, special codes are used by the Iwireline industry to direct calls to specific OTHER CODES: Codes 000-199 call types, features or service providers (See y definition, the codes 000-199 were TABLE 3 in the Appendix). These codes B excluded from the original NANP are usually listed as prefixes or access codes. format and all subsequent redefinitions. The Switching system digit analysis cannot values 0 and 1 in the “A” and “D’ digit process, conflicting, multiple uses of the positions of a NANP number, creates the same digits without a software trigger to codes 000-199. These codes were excluded cause the switch to query a database for so that there would be no customer additional routing information. These confusion or switching conflicts with database queries are associated with prefixes such as 11X. The definitions and Intelligent and Advanced Intelligent intent of the uses of the NANP requires Networks. (IN & ALN).’ IN and AIN some further clarification of codes 000-199. features can only be provided in stored program controlled switching systems. The industry has always needed additional codes: in the same basic format or length for OTHER CODES: Star * and Number use in the telephone industry to perform Sign other functions. Some of these functions o minimize the amount of confusion precede customer dialing of long distance Texperienced by callers using these calls. Since the values, of the codes, 000- characters, there was an effort to standardize 199 are not part of the defined NANP format their use. It is also important that consistent for either of the first two codes, these values terminology be known and ,used when can, and are, used for these other functions. referring to these characters. The (#) and Industry and regulatory discussions for the (*) should be called the number sign and using the codes 000-199, for CO Code the star, respectively. The terms number relief, are defined as “DDigit Release. sign and star have been internationally agreed upon. Use of the terms asterisk for Because of the NANP exclusion, the codes (*) and pound sign for (#) should nor be 000-199 are used by the telephone industry used in documentation dealing with dialing for Test Codes, Inward Operator Codes, procedures. Special Billing Numbers, Revenue Accounting Office (RAO) Credit Card Currently, the characters (it) and (*) have the Numbers and special routing of calls. Most following general applications: of these codes cannot be dialed by end users. Various switching systems have software 1.) The first use of the number sign (#) is as checks that block calls to and from numbers an end-of-dialing or concludes the present with these values. These software checks action and proceeds to the next action were installed to minimize fraud. Operator indicator. This end-of-dialing use exists Services switching systems have software today and avoids a timing period (for tables to validate credit card calls that utilize example, IDDD) using certain types of these codes. switching systems. The conclude-and-

AT&T Technical Advisory #3, NPL 81-09-27, Issue 2, December I, 1981

Version 1.00 Page 19 of 63 February 2004 UNDERSTANDING THE PUBLIC SWITCHED TELEPHONE NETWORK proceed use also occurs in some telephone when placing automated calling card billed credit card services where the customer calls. Instead of the customer hanging-up wants to indicate that the present call is over and redialing when detecting a keying error and a new call is about to be placed (for (before the card system detects the keyed example, sequence calling). error), the caller can simply enter the (*) button to back-up to some pre-established 2.) The second use of the number sign (#) is point and redial the segment in which an as the first character when dialing a call that error was recognized by the caller. is a wideband or other data call requiring special treatment. In certain types of data N11 AND NO0 Codes calls, both an initial and concluding (#) may uring the development of the NANP, be required. Functionally, this is similar in DN11 Codes were reserved for telephone many respects to the KP + (address) + ST company services to replace the older 11X multi-frequency signaling format used by codes. Some local dial switching systems operators. (i.e. Cross-Bar) used these N11 codes before the NANP was codified. (See TABLE 6 in There are also a number of nonstandard the Appendix for N11 Codes) Excluding the uses of the # sign for PlN Number Calling N11 codes, the original NANP, format and features. The # sign is also used in a values, defined 152 Area Codes and 540 CO number of ancillary equipment attached to Codes within each Area Code. The NANP the PSTN. An example of this is voice mail. went into service with 86 Area Codes.

3.) The first use of the star (*) is as a prefix NO0 codes were reserved for future uses. when dialing a Vertical Service Code (VSC) The first of these uses was the 800 code for (for example, call forwarding) of the form non-geographic automatic collect calls. This *XX(X). In this application, the (*) dial access, to collect calls, replaced the old indicates to the switching system that the manual operator Enterprise, Zenith and WX digits following specify a certain desired services. (See TABLE 7 in the Appendix feature/service. for NO0 Codes)

In order to allow rotary dial telephone GROWTH OF AREA CODES AND CO access to vertical service codes, the digits 11 CODES are translated to simulate the star key in ne of two methods was used in the stored program controlled switches. 0early days of the NANP to handle growth in certain areas. These were: Vertical Service Codes are classed as numbering resources. Their assignment is 1) Split the existing NPA into two covered in INC documents and they are parts and assign a new NPA to administered by NANPA. one of the parts.

4.) The second major use of the (*) button is 2) Realign the boundary between to provide an error correcting function for two existing NPAs so that a customer-dialing of various strings on a better balance is achieved in the sequential basis in response to prompting. number of telephones in each This could include a customer interactive NPA. session with an operator services system

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I In the 1970s, a third method was added to systems. This change began in 1959 and this list. The third method involved was not fully completed until 1980. Even overlaying an existing Area Code(s) with the though we are “officially” on an ANC basis, new code, thus having two area, codes there is nothing which prohibits one from service the exact same geographical area. still quoting their, telephone number with the This method mandates 10 digit local dialing. old exchange name. ANC was’ a public relations nightmare in many large cities, ,‘in Growth, in CO Codes, was handled in one of the US., where people associated their three ways. These were: social status by the exchange name”.

Assignment of a new CO Code to ADDITIONAL CO CODES WITHIN an existing Central Office EACH NPA - PHASE I1 n the early 1970s, certain NPAs were Construction of a new Central Iagain forecasted to exhaust their available Office with new codes CO Codes. ” Switch technology had progressed to the point to where some of the Realign the boundary between original restrictions in code format were no two existing Central Offices so longer necessary. The Bell System ’ that a better balance is achieved expanded the number of available CO Codes in the number of telephones in in each NPA by changing the fdrmat of the each CO Code. CO Code from NNX to NXX. This plan added 160 CO Codes to each NPA for a new These plans necessitated numbering changes total of 800. This plan required that new for some subscribers in the affected areas. specifications and development be done to The industry has always had permissive existing ‘switch and Operational Support . , dialing periods where both codes could be System (OSS) requirements, The name of used to reach the same number until this plan was E-digit Unblocking. customers became familiar with the new dialing pattern. ADDITIONAL AREA CODES n the late 1980s, it was forecasted that the With only rare exceptions, new Area Codes Isupply of 152 NPA Codes would exhaust or Central Office Codes were put in service by the mid 1990s. The industry developed a coincident with the delivery of a new plan to redefine the NPA Code format from telephone directory. N (0 or 1) X to NXX. This plan was developed by Bellcore on behalf of the ADDITIONAL CO CODES WITHIN seven Regional Bell Operating Companies. EACH NPA - PHASE I This plan made the entire number of CO y the end of the 1950s, certain Area Codes available as Area Codes. This plan B Codes were running out of CO Codes. added 640 NPA Codes to the existing The Bell System expanded the CO Code quantity of 152 and brought the total of resource by converting to All Number NPAs available to 792. This plan took Calling (ANC). This replaced the 2-letter, considerable planning, technical 5-digit numbering scheme. This added 100 CO Codes in each existing NPA for a new total of 640. This change was administrative 10 “Telephone, The First Hundred Years” by John and needed no changes in switching Brooks and published by Harper & Row, Publishers in 1976.

Version I00 Page 2 I of 63 February ?004 -_ UNDERSTANDING__- THE PL’RI~ICSWITCHED TELEPHONE NETWORK specification work and ‘switch development. METHODOLOGY FOR ROUTIAG

It took over 5 years to implement. ,, , AND RATING ach Wire Center and each Rate Center This change necessitated changes is switch , Ewere (and still are) given vertical and functions to allow timing delay sequences to horizontal map coordinates (V&H). Call be initiated in areas that had ambiguous routing and call rating are done by analysis Area Codes and CO Codes. This timing of NPA NXX to NPA NXX. Bt, subtractibn delay ‘sequence can be eliminated by having of the V&H coordinates, and the use of the mandatory ten digit dialing. Pythagorean Theorem, the airline miles between any two rate centers can be CALL ROUTING AND RATING: determined”. These miles are converted to ust having a ten digit telephone rate steps. Tariff charges, per rate step, are J number does not assure one of being filed with respective state and federal able to make or receive telephone calls. regulatory agencies. Thesecharges form the Calls must be’routed and properly billed distance portion of chargeable calls. Local by a comprehensive uniform plan for calling areas were established by figuring at rating and routing of messages. what distance the processing of.the charges became more expensive than the collection The combination of Area Code plus CO of the charges. Code defined the calling party’s switching system and the called party’s switching Airline miles between wire centers and system. In addition, the combination of points of connection are used to determine Area Code and CO Code defined the rate the distance portion of Carrier Access centers of the calling and called numbers. Billing (CABS) and for Meet Point billing

The switching system location defined the between phone companies. ’ . ’ ’. “wire center’’ for call routing purposes. The rate center defined the geographic Routing a call was simple ‘in the original destination for customer billing purposes. plan. Switching systems were assigned in a Rate Center definitions are filed in tariffs particular NPA and this was called the with the FCC and various state regulatory Home Numbering Plan Area (“PA). A agencies. Wire Center and Rate Center call to any other area code was to a Foreign destinations can be the same, but their Numbering Plan Area (FNPA). Any ten definitions and uses reside in different digit call to an FNPA was routed to AT&T. industry data bases. Wire Center AT&T routed the call according to the information is “programmed into switch switching plan. The philosophy of routing routing tables and Rate Center information was to complete the call as quickly as is “programmed” into computing systems possible with a low probability of call used to generate billing information based failure. upon dialed digits. Since the telephone industry only rates and In other words, calls were routed from routes calls based upon the first six digits of the switch that contained the calling a telephone number, there are millions of party’s line and number to the switch that numbers that cannot be used because of the contained the called party’s line and geographic reliance of the first six digits. number. II Telcordia Notes on V&H Coordinates, SR-Notes- Series-20

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Regulators and other public officials recognize that there are more numbers than (Even though a NANP number format is people and think this is a problem that the illustrated as NXX-NXX-XXXX, its ITU telephone industry is perpetuating upon the E.164 number is illustrated as I-NXX-NXX- general public in order to raise rates and XXXX, since the Country Code for North confuse customers. America is 1.

Wireline telephone numbers were created EXPANDED INTERNATIONAL with geographic significance. CMRS DIALING number assignment followed that n the late 1980s, the International geographic significance based upon the ITelecommunications Union (ITU) location of the serving CMRS switch. realized that the world was exhausting its However, CMRS roaming removes that numbering ability to handle new entrants geographic significance. In addition, large into the world of International Direct metropolitan areas have added so many new Distance Dialing. This was exacerbated by codes, due to demand, that the geographic the break up of the Soviet Union and the significance has diminished. splits in Eastern Europe. The ITU issued its Recommendation E. 164 “Public The PSTN was designed, coordinated, Telecommunications Numbering Plan”. managed and maintained by AT&T Network This recommendation expanded the amount Planning until the break up of the Bell of digits needed for IDDD from 12 digits to System in 1984. The PSTN was then 15 digits. This expansion took considerable administered by Bell Communications standards work on switching, billing and Research Corporation (Bellcore) on behalf other operational support systems OSSs. of the seven Regional Bell Operating This expansion took place on January 1, Companies (RBOCs) until the 1997. Telecommunications Act of 1996 (TA-96). The US. FCC, in cooperation with the INDUSTRY CONTROL OF NUMBERS telephone industry and state regulators, elephone numbering resources are contracted the administration of the Tthe “source code” by which the numbering resources to NeuStar (See Public Switched Network (PSTN) TABLE 1 in the Appendix). The Canadian elements function. Each technology that CRTC awarded the contract to SAIC Canada uses NANP numbering resources is to administer telephone numbers in Canada. constructed using the format and values of The telephone industry is still developing the Plan. refinements in the administration of the NANP. Electro-mechanical telephone central offices had to be provisioned with physical Even though the NANP preceded it, the switching equipment to complete calls to NANP follows international standards and is telephone numbers. Stored program compliant with the International controlled systems only have computer Telecommunications Union (IW memory addresses associated with numbers. Recommendation E.164 “Public Stored program controlled switching Telecommunications Numbering Plan” (See systems use the numbers to obtain the TABLE 2 in the Appendix). This is address location of the physical line essential for participation in International equipment (line number) that connects the Direct Distance Dialing (IDDD).

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* customer to the switch.' Telephone numbers offices could then be done with a minimal are signaled between switching systems,, to amount of digits to minimize switching complete telephone calls. The calling equipment requirements and to speed up party's telephone number and the called connections. In other words, if a switch party's telephone number are parts of the only needed 4 digits to complete a call, the data recorded on message accounting media tandem office would only forward 4 digits to for proper billing. that switch. I

Control of the assignment of Area Codes CO Codes with high numbers (Le. 998) or and Central Office Codes were as important numbers that did not fit into large city to telephone companies as the use of the dialing plans were assigned to rural areas numbers themselves. AT&T controlled the that did not have a large calling area. assignment of Area Codes and the Bell Operating, Companies controlled the A11 of this caused a high number of CO assignment of CO Codes. Heavy traffic codes to be' reserved for future use in volume areas were assigned area codes specific areas. based upon minimizing the spin of a rotary dial for areas that had large long distance Historically, the telephone industry has call volumes. In addition, switching routed telephone calls based upon three or ' equipment work times, in these areas, were six digits in order to minimize delays in calls minimized due to a smaller count of dial caused by digit analysis. Each of the codes pulses generated by the caller (or operator) in the original NANP had different formats. and received by the equipment. Area Codes Electro-mechanical switch decisions relied with a 0 as the central digit were assigned to on the two codes being different in order to states ,or provinces that were expected to minimize timing, delays in ca1l"processing. have only 1 Area Code. Area Codes with a Subsequent redefinitions of NANP values 1 as the central digit were assigned to states have resulted in the format of these two or provinces that were expected to have codes being exactly the same. The multiple Area Codes. necessary information, needed for call routing instructions, is now contained in the In cities that had step-by-step switching TelcordiaTM LERGTMRouting Guide. The equipment, it was advantageous to grow rating information is based upon data with new CO Codes that would have the contained in the TelcordiaTM TPMTM Data same first two digits as the existing NNXs. Source. This kept the same geographic name and meaning as existing codes and lessened the CMRS SERVICE PROVIDERS need for intermediate selector additions to (CELLULAR AND PCS) USES OF the equipment. Telephone numbers could NUMBERS not be assigned in sequence in these offices, ven though the Wireless Industry because traffic load balance needed to be Eutilizes NANP numbering resources, it evenly spread over the switching equipment does not always use standard prefixes or that was associated with telephone numbers. access codes. The wireless industry also has other numbering requirements, separate In addition, cities with large metropolitan from the number associated with the CMRS calling areas needed new CO codes that subscriber. Most of these requirements are could be handled easily in step-by-step necessitated by CMRS roaming and access tandems. Call signaling, between central

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to emergency services via 9-1-1 (See switches. Even though CMRS switches TABLE 9 in the Appendix). perform the same function as wireline switches, they interconnect in different Mobile Telephone Service (MTS) was manners 12 . CMRS interconnection to the developed by the Bell System and PSTN follows much the same methods that introduced in 1946. Mobile telephones were the Bell System developed for IMTS in the connected to the network by using adjunct 1950s. CMRS service providers also have radio equipment interfaced into existing different regulatory rules. They can cross electro-mechanical switching systems on a LATA and state boundaries. line and/or trunk basis. This adjunct equipment connected switches to radio Evolution in inter-company business antennas for connection to the mobile arrangements, and instrument capabilities phones. Roaming was handled by have expanded the role of CMRS roaming connection to a live telephone operator in a into true portability. However, roaming toll center. Telephone numbers associated necessitates the need for an additional with mobile phones were part of the serving number to be assigned to the roamer for telephone switching office. MTS evolved message rating purposes. Even though the into Improved Mobile Telephone Service end user pays a flat rate and has nationwide (IMTS) in the early 1950s. IMTS was free roaming, the inter-company billing expensive and unreliable. arrangements still are based upon point of origin to point of termination. Local taxes Cellular technology was invented before the applied to these calls are also dependent on breakup of AT&T (MFJ). However, the the jurisdiction of the originating location deployment of the technology did not occur and the terminating location. Emergency until after the MFJ. Early cellular access code (9-1-1) requirements also technology was expensive, bulky and had necessitate other temporary numbers he sporadic service areas. PCS technology assigned to a CMRS roamers. All of this occurred later, but PCS number usage and complicates telephone number demand. interconnection follows the same pattern as cellular. Initial deployment of this CMRS The current NANP format enables the form of telecommunications was slow to CMRS Industry segment to utilize deploy due to the expense and the numbering resources listed in TABLE 9 of complexity of the instruments. CMRS the Appendix. Unless otherwise noted, switching systems were no longer adjuncts numbers so utilized cannot be used for other and are the CMRS equivalent to the wireline purposes such as assignment to subscribers. end office. CMRS systems are only wireless from the customer instrument to PACKET NETWORKS (VToA AND the first tower site. After that, they must VoIP) USE OF NUMBERS connect and switch through the wireline nd users of telephone services want to network, unless the call is between two Ereach the person they called. They do CMRS customers served by the same not care what technology is deployed switching system. between them and the party they are calling, The PSTN was created to be independent of Technological differences have allowed technology. End users also want reliable CMRS switching systems to serve much inexpensive service. Packet technology has larger geographic areas than wireline Wireless Basics 2”d Edition by Harry E. Young

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existed for decades and has been used to batteries could be maintained at the Central transmit data. It is also used by the Office. The first Common Battery system telephone industry for the signaling portion was put into service in Worcester, of the voice network. Early trials of Massachusetts, in 1896. transmitting voice over this type of network proved to be unreliable and of poor quality. Telephones are still DC powered. This is Recent technology improvements have important, because the loop resistance is still solved most of those early problems. Packet a deciding factor in wireline telephone switching is now beginning to be deployed signaling. This loop design includes the for use in voice networks. Packet resistance of the telephone set. Wire technology uses of numbering resources will Centers are constructed in order to adhere to depend largely on how this technology Ohm’s Law. The Bell System constantly interfaces and interoperates with the existing improved the capabilities of telephone sets Public Switched Telephone Network to lower the resistance. The power standard (PSTN). Co-existence is essential for proper that was developed in the early years was 48 evolution and transformation from circuit Volts, DC. switched to packet switched networks. If this technology interfaces are an adjunct to Telephone switching systems are still the existing PSTN, then the use of telephone powered by batteries. Batteries can also numbers could be different than the existing serve as back up, when electricity is architecture. This technology may not need interrupted. They also serve as a filter to traditional telephone numbers at all. If this eliminate random electrically generated technology is defined and interfaces in the noises from AC power. Commercial electric same way as circuit switched voice, then the power is used to charge the batteries. impact on numbering will be minimal. Only Standards have been developed to provide time and consensus standards can determine sufficient battery life to power the phone the long range impact on the NANP. system for a number of hours when commercial power is interrupted. Federal Section 4 - The Nationwide Toll Dialing and State regulations have been established -Plan to mandate the amount of time needed to sustain telephone service in times of POWERING THE SYSTEM commercial power failure. In modern times, he original telephones each had their most telephone Central Offices have been Town batteries that supplied power. A provided with a back up generator to crank on the side of the phone generated provide the electricity to charge the batteries additional electricity that rang the phones, when commercial power fails. Telephone on the line, when the crank was turned and system practices and standards have been the phones were on their hook. Telephone developed to maintain the batteries and companies sold Dry Cell Batteries for the generators so that they are always in top phones. As each phone’s batteries condition. Battery life cycles have been discharged, the transmission quality calculated and the batteries are replaced on decreased. Sending someone out to replace regular intervals. the batteries became a chore. Later systems provided the battery power back at the The button that pushes down when you hang Central Office. This newer type of phone up the phone is still called the switch hook. system was called “Common Battery”. The It is named after the switch on the side of the

Vnsion 1.W Page 26 of 63 February 2004 UNDERSTA~INGTHE PUBLIC SWITCHED TELEPHONE NETWORK phone that looked like a hook. The receiver CONNECTION TO THE SYSTEM (the .part that you put up to your ear) had an ommunity “eye” attached to its top and the “eye” part Cswitchboards was hung on the hook. The hook pulled were placed in down from the weight of the receiver and central locations, opened ,a switch that disconnected the phone usually in the main from the line. When the receiver was office of the phone removed from the hook, spring pressure company. In moved the hook upward closing the switch smaller and the phone was then connected to the communities, this line. This connection caused current to flow could be the home and lit a lamp at the local switchboard. In of the telephone old movies, you sometimes see an actor operator. These quickly moving the switch hook up and became known as the Central Office. Each down. This caused the operator lamp to and every phone line had a physical pair of flash. Customers had the mistaken, wires connecting it to the central office. impression that this would cause the Each and every phone line had a resistance operitor to answer the call faster. The flow limit that determined how far away from the of, current in dial systems caused the Central Office it could be located. For all customer to be connected to the dial tone intensive purposes, this loop resistance limit source. still exists. (Electronics and computerization have created “simulated” The most common form of signaling a cable pair connections to the Central Office phone to ring is called “superimposed”. that can increase the distance the end user This method puts Alternating Current (AC) can be from the switching equipment.) out on the telephone wire loop. The phone Operators physically answered each call and is on the hook, so the loop is open. manually connected the parties with a patch However, a coil is across the line. The AC cord. The operator positions had cord pairs. energizes the coil, which then causes the The front cord answered the call and the ringer to operate. back cord connected the call forward. Small town operators knew everyone and knew The other major phone signaling situation where everyone was. They could connect occurs when someone picks up the phone you to your party even though the person handset. This closes the switch and causes was at someone else’s house. This was an current to flow in the loop. In the early early form of “Call Forwarding”. If the line days, this caused a lamp to light in the you were calling was in use, the operator switchboard. In dial systems, it caused the informed you that the line was “busy”. electro-mechanical switch to find the line the current was flowing from and connect it The switchboards in various cities and towns to dial tone. In modem stored program were interconnected, electrically, by controlled systems, the current flow causes a facilities called trunk lines. This term is still computer processor to recognize a change in used to define interconnection facilities. state and connect the phone to dial tone and devices to capture digits dialed or pulsed. By the 1930s, most metropolitan areas of North America had replaced local telephone operators with automated switching systems.

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These automated systems were for high volume weekday business hours interconnected by trunk lines or trunks as and lower rates for weekends, evenings and they ultimately became known. Accessing nights. Long distance charges were inflated long distance could be done by dialing 112 to offset the high cost of building out the or dialing 0 and asking for the long distance telephone system to rural areas. This build operator. The operators associated with out followed the Universal Service goal dialing 0 usually worked for the local mentioned earlier. telephone company and the long distance operators worked for AT&T. The Bell System realized that considerable operator work times could be saved if the AUTOMATING THE LONG call routing decisions were made DISTANCE OPERATOR automatically rior to automation, telephone operators Phad precise written directions for In the 1930s, Bell Telephone Laboratories placing long distance calls. They also did was busy trying to develop new and faster not have trunks to every place needed. switching systems. They settled on the use These directions were created to minimize of a crossbar switch technology patented by the amount of switchboards that needed L. M. Ericsson Company in Sweden. The interconnection in a given long distance call. original production models of these crossbar This was done to minimize the transmission switches were deployed in the larger loss to enable the customers to hear each metropolitan areas of the US. and Canada other. before operator automation. Additional work continued on these types of switches to An operator would accept the call from an automate the routing of long distance calls end user and call back the end user when the placed by operators. World War 11 put a long distance call was set up. An operator temporary delay on the deployment of this would call another operator up the chain to technology. place the call. That operator would then call the next operator until the call was set up The Bell System published the Operator Toll from one locality to the locality of the Dialing Plan, on October 22, 1947, utilizing receiving end user. The original operator the unique ten digits created by the NANP would call back the call originator and and the newer switch technologies. The announce that the called party was on the Operator Toll Dialing Plan was shared with line. If any operator in the route of the call the independent operating telephone set up encountered an all circuits busy companies through the United States condition, the call would be terminated until Independent Telephone Association. an idle circuit became available. The process then started all over. During busy The Operator Toll Dialing Plan, was created times, a long distance call might take hours utilizing a hierarchical switching to complete. However, the originating arrangement (see Appendix, Figure 1) that customer only paid for the call if and when assured that no telephone call would switch it completed. Billing was set up based on more than ten times”. This switching plan the distance of the call and the time involved was designed to minimize the probability of in the conversation. Prices varied dependent encountering an “All Trunks Busy” upon the time of day and the day of the week. This system charged premium rates l3 Bcll System (AT&T) “Notes on Distance Dialing”, 1975

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I condition and to maintain a consistent took all of the wires from the *various volume level for speech quality. The speed telephones and connected them via patch and architecture of the switching plan cords. The first commercial switchboard enabled long distance calls to be made was placed into service on January 28, 1878 faster, which lessened operator work times. in New Haven, Connecticut. Initial This reduced the need for operators. This telephone systems were magneto sets that Plan was totally dependent upon the were self powered and generated ringgng geographic significance and uniqueness of current via a hand cranked magneto. The the numbering system. central switchboard also signaled in the same manner. In other words, you cranked This plan worked because each end user had your telephone to signal the operator and the ,,unique ten digit telephone number picked up the receiver and waited for her to created by the plan and the switching plan answer. When the operator forwarded the was uniform and seamless. The first six call, the operator cranked a magneto to ring digits of the telephone number identified the the called party. As switchboard size grew, wire center and rate center of the called additional positions were added and number. Routing was accomplished in the additional jack strips were added up to the switches associated with the plan. Trunk height that could be reached by an operator. interconnections and digit translation Early switchboards evolved into common ’ assured the fixed availability of the system. battery systems where the power was furnished at the Central Office and ringing CUSTOMER bIALING OF LONG could be applied by throwing a key to apply DISTANCE ring current. Common Battery systems only he next step was to connect the local became viable after, the deployment of Tswitches to the switches utilized by the commercial elecrrical power. ’ Operator Toll Dialing Plan. This connection started in the early 1950s and Englewood, DIAL SYSTEMS New Jersey became the first community to he demand for telephone service and the access DDD on November 10, 1951. DDD Tincreased traffic generated by each was completed to most areas of North telephone user soon created a need to America by the mid-1960s. automate the placement of calls. This requirement was also needed to reduce the In 1955, the AT&T Notes on Distance need to hire more telephone operators. Dialing officially changed the name of the Plan to the North American Numbering Plan Telephone equipment (NANP). engineers looked to the Almon Strowger Section 5 - Evolution of Technology invention and began to build systems based upon s soon as there were the concept. This A more than two equipment was called telephones that needed to Steo-bv-Steu. It was so -I be interconnected, a named because each digit dialed would method was needed to “step” a switch the amount of levels accomplish this feat. indicated by the dialed digit. The limitations This need produced the of this technology were the traffic that could switchboard. This device

Version 1 .SKI Pagc 29 of 63 February 2004 UNDERSTANDING THE PUBLIC SWITCHED TELEPHONE NETWORK be handled by the switching limitations for conversation, once the call is set up. imposed by a base ten system. In other This signaling could be in the form of “dial words, any given element of the system pulse” or Multi-Frequency”. In the 197Os, could only access ten elements in the next AT&T developed a program to increase the switching stage. These elements were also percentage of billable traffic that was shared with other accesses. This created a completed on the network. Part of this complicated method for traffic engineering effort was the development of Common and traffic load balance. Channel Signaling (CCS). CCS performed interoffice signaling on a separate path than In the early 1930s, Bell the path used for conversation. This system engineers began looking was only deployed in the long distance part to another system of the PSTN. After deployment, only valid developed by L. M. billable messages were carried on the voice Ericsson in Sweden. path. This system utilized a different switching International standards bodies were also in arrangement and was the process of developing CCS and called Crossbar. This developed a method called CCS7. AT&T switch type could be interconnected to carry adoptcd the standards used for CCS7 for the much larger amounts of traffic. The most PSTN. These standards were modified for common local office Crossbar switches, in North America due to different information the Bell System, were the #I Crossbar and requirements. International carriers deploy the #5 Crossbar. The #4 Crossbar was used “Gateway” offices that convert international exclusively for toll switching. The #I CCS7 messages to North American CCS7 Crossbar and the #5 Crossbar could also be messages and vice-versa. adapted to toll switching applications. In the PSTN, this signaling method is just Various equipment suppliers developed referred to as SS7. SS7 is important as it is equipment for the independent telephone necessary for the telephone network to be companies. Most of these were adaptations able to perform tasks later mandated by the of Step-by-step or Crossbar technology. MFJ and TA-96.

The Nationwide Toll Dialing Plan was SUMMARY - 1947 - 1983 created to be independent of the type of he Telephone Systems in the United switching equipment using the PSTN. The TStates and Canada handle millions of PSTN allows all types of equipment to use toll calls a day. These were routed over a it. How a particular piece of equipment is network of long haul intertoll trunks which used determines its definition in the interconnected approximately 2,600 toll switching plan hierarchy. As switching switching offices and, with a few equipment evolved, it fit into the application exceptions, all of the telephones in these two for which it was intended in the PSTN. countries.

INTEROFFICE SIGNALING Large volumes of traffic between toll offices he design and implementation of the were generally routed economically over TPSTN allowed interswitch signaling to direct intertoll trunks. When the volume of be done on the same path that would be used traffic was small, however, the use of direct

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, trunks was usually not economical. In these THE PAST - 1983 - 1996 cases the traffic was then handled by connecting together, by means of switching Section 1 - Regulator1 equipment at intermediate toll offices, two or more intertoll trunks to "build up" the MODIFICATION OF FINAL required circuit. "Built-up" connections JUDGMENT (MFJ) involved several intertoll switching points if n November 1974, the US. department'of the originating and terminating points were a IJustice filed an antitrust lawsuit against great distance apart and the traffic volume AT&T. In January 1982, the parties reached was small. Although this multi-switched a settlement. This settlement had AT&T traffic constituted only a small portion of the divest itself of their local telephone total, it was important that telephone plant company subsidiaries. AT&T retained be designed to care for it as well as for the control of their long distance subsidiary, greater volume that was handled via the less their manufacturing arm (Western Electric) complex direct and single switch routes. and their Operator Services business. This is referred to as the Modification of Final The conditions under which toll traffic was Judgment (MFJ). automatically switched on a nationwide scale were quite similar to those found in Prior to the MFJ, the PSTN was designed large cities with large volumes of traffic and defined by engineers based upon service between many separate switching centers. requirements based upon actual traffic Therefore, experience gained in these places measurements. After the MFJ, the PSTN was applied to the nationwide dialing job. was driven by economists.

The needs Of multi-office exchange areas The Department of Justice's 'MFJ broke were met by switching and trunking plans the seamless national network into 164 that employed a new principle, "automatic separate pieces called Local Access and alternate routing", to provide rapid and Transport Areas (LATAs) io handle local accurate connections with few occasions for phone traffic. Through this move the DOJ repeated attempts (see Appendix, Figure 1). created two distinct types of service With this principle, a call which encounters providers: local exchange carriers (LECs) an all trunks busy signal on the first route and interexchange carriers (IXCs)." tested was automatically and rapidly "route advanced" and offered to one or more All calling between LATAs had to be alternate routes, in sequence.I4 handed off to the new competitive Interexchange Carriers (IXCs). Up until 1983, AT&T controlled the end to end connections for all telephone calls in the Even though the MFJ created LATAs, the US. This was done through their Bell actual area that defined each LATA was Operating Companies and various defined by the new RBOCs. The en,'Oineers independent telephone companies that associated with designing and administering followed the same interconnections the trunking in each area, were given the standards and philosophies as the Bell task of LATA definition. Hence, each System. In essence, the PSTN was a LATA coincided with the area of seamless network. l4 http://www.telephonetribute.com/ IS http://www.be1lsys1emmemorial.com/

Version 1 .W Page 3 I of 63 February 2W4 UNDERSTANDING THE PUBLIC SWITCHED TELEPHONE NETWORK responsibility for these engineering groups. The Ohio B,ell Telephone Cdmpany Later, independent telephone companies Wisconsin Telephone Company established their own LATAs and LATA connection points. Bell Atlantic New Jersey Bell Telephone The MFJ created four basic jurisdictions of Company calls in the United States. The Bell Telephone Company :of Pennsylvania 1. Local area calls The Diamond State ' Telephone 2. IntraLATA - Intra-State calls Company 3. InterLATA - Intra-State calls The Chesapeake and Potomac 4. InterLATA - Inter-State calls Telephone Company The Chesapeake and Potomac The first,three categories are regulated by Telephone Company of Maryland state public utilities commissions and the The I Chesapeake and Potomac last category,isregulated by the FCC Telephone Company of Virginia The Chesapeake and Potomac Telephone traffic to each of these Telephone Company of West jurisdictions must be routed over separate Virginia trunk groups in order to properly categorize the investments and costs for each category. BellSouth This is done for rate . development, South Central Bell Telephone intercompany billing, taxation and revenue Company division. Southern Bell Telephone and

Telegraph Company. " The basic premise of the MFJ was to allow competition in the Long Distance toll Nynex business. LECs were only allowed to handle New England Telephone and local and IntraLATA toll traffic. All Telegraph Company InterLATA toll traffic had to hand off to an New York Telephone Company IXC. The LEC restrictions were only mandated to the Bell operating companies Pacific Telesis Group and GTE but applied to other phone The Pacific Bell Telephone and companies that had valid requests from Telegraph Company Ixcs. Nevada Bell

REGIONAL BELL OPERATING Southwestern Bell Corporation COMPANIES (RBOCS) Southwestern Bell Telephone Co. he seven RBOCs created by the MFJ Twere: US West The Mountain States Telephone and Ameritech Telegraph Company Illinois Bell Telephone Company Northwestern Bell Telephone Indiana Bell Telephone Company, Company Inc. Pacific Northwest Bell Telephone Michigan Bell Telephone Company Company

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