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Home , Agere Systems, Automatic Electric, Panel switch, Stepping switch, Strowger switch, Telephone exchange

School of Science and Technology

Assignment: Search On / AT&T Technologies / Systems

Resource Person: Mr. Khalid Asghar

Coarse title and Code: Telecom Switching and Transmission

Section: A

Submitted By: M Junaid

University ID No: 091420310

Date/Day of Submission: Monday 07-10-2013

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Introduction of Western Electric: Western Electric Company was an American electrical engineering and manufacturing company, the supplier to AT&T from 1881 to 1995. It was the scene of a number of technological innovations and also some seminal developments in industrial management. It also served as the purchasing agent for the member companies of the .

Technical Innovations:

The year 1936 brought the introduction of the Model 302 , the first Western Electric instrument that combined the desktop telephone mount with the subscriber set and ringer in one unit. The design was conceived by the engineering firm of industrial designer Henry Dreyfuss. and it was the mainstay of American telephone service until 1949, when it was followed by the , which would become the most extensively produced telephone model in the industry's history. It was continually updated over time, reflecting new materials and manufacturing processes, such as quieter and smoother dial gearing and a printed circuit board for the network electronics. The Model 500 was discontinued in 1986, in favor of a Touch-Tone version, Model 2500, that employed in-band signaling of the dialed digits, using Dual-Tone Multi-Frequency (DTMF). DTMF was generally referred to by the trademarked name, Touch-Tone.

Other innovations included the Princess of the 1950s and Trimline telephones of the 1960s, and the development of Touch-Tone dialing as a replacement for rotary dialing.

In 1929, Western Electric also entered as a competitor in early cinema sound systems. It created the Western Electric Universal Base, a device by which early silent cinema projectors could be adapted to screen sound films. It also designed a wide-audio-range horn loudspeaker for cinemas. This was estimated to be nearly 50% efficient, thus allowing a cinema to be filled with sound from a 3-watt amplifier. This was an important breakthrough in 1929 because high-powered audio valves were not generally available.

Western Electric's switching equipment included the development of the Electronic Switching System (ESS). The No. 1 ESS was first installed in 1963. The 4ESS was the first digital toll switching system, implemented in 1976. Finally, in 1981, the first widespread digital switching system, the 5ESS was implemented throughout the United States.

The end of Western Electric (AT&T, Lucent): Western Electric came to an end in 1995 when AT&T changed the name of AT&T Technologies to Lucent Technologies, in preparation for its spinoff. All modular telephone plugs were now marked with "HHE" enclosed in an oval. Lucent became independent in 1996, and sold more assets into Advanced American Telephones, Agere Systems, , and Consumer Phone Services. Lucent itself merged with Alcatel, forming Alcatel-Lucent. Western Electric's Structured Cabling unit, once known as AT&T Network Systems or SYSTIMAX, was spun off from Avaya and is now part of CommScope.

Panel :

The panel switching system was an early type of automatic , first put into urban service by the Bell System in the 1920s and removed during the 1970s. The Panel and Rotary systems were developed in parallel by Western Electric Labs (later called ) in the U.S. and International Western Electric in Belgium before World War I and had many features in common, though the Rotary system was used in Europe.

The first Panel exchange was installed at the Mulberry Central Office in Newark, New Jersey. It was placed in service on January 16, 1915. It was a semi-automatic system using non-dial telephones. The next installation was in the Waverly C.O. June 12th. of the same year, also in Newark, NJ.

The Panel Machine Switching System (M.S.S.) was named for its tall panels covered with 500 rows of terminals. Each panel had an electric motor, to drive its (usually sixty) selectors by electromagnetically controlled clutches. The selector was similar in effect to a though it moved continuously rather than in steps. Each selector had five brushes, any of which had 100 terminals among which it could select, arranged in groups. Pulses were sent back from the selector to a Register which had received the dialed digits, rather than forward as in the SXS system, hence the signaling was called "Revertive Pulse". Office Select Tandem and : By the early 1940s, Western Electric realized that the XBT was not enough to handle the many long distance calls that were placed daily. A much more robust switch needed to be developed.

The #4 Crossbar switch was developed to meet this need. The first installation of the #4 Crossbar was at Philadelphia in 1943. Further installations were put on hold until after World War II. Subsequent installations started up again in 1948 and 1949 in New York, , Cleveland, Oakland (CA) and Boston.

By 1950, Western Eclectic had anticipated the need for the #4 Crossbar to change “routing translations” dynamically when needed, instead of being hard wired. New #4 Crossbar were called #A4A for “Anticipated #4 Advanced”. These machines were installed between 1950 and 1953.

By 1953, a “card translator” system had been developed using punched metal cards and light detecting “photo cells” would detect patterns in these punched cards to determine routing transitions and alternate routing translations (if the first routing was busy). The new #4 Crossbar switches were called #4A (#4 Advanced). The existing #4 Crossbar switches were modified for use with the card translator – their names became #4M (#4 Modified). The #4A switches were installed between 1953 and 1968.

By 1969, an electronic equivalent of the mechanical card translator system had been developed. Further installations of the #4 Crossbar switch utilized this new system. They were referred to as #4-ETS (Electronic Translator System). Some existing #4 Crossbar switches were modified to use the ETS, but not all. The ETS line of #4 Crossbar switches lasted from 1969 through the end of the #4 Crossbar line in 1976.

The #4 Crossbar series of switches were in service until the 1980s when they were replaced with the #4ESS series of digital tandem switches.

Strowger Switch:

The commercial version of the , as developed by the Strowger Automatic Telephone Exchange Company, used a for signaling to the exchange. The original final selector (connector) switch which connected to 100 customers was supplemented by preceding group selector stages, as the "cascading" enabled connection to many more customers, and to customers at other exchanges. Another requirement for commercial systems was a circuit to detect a busy connection (line) and return a busy signal to the calling subscriber.

Instead of dedicating an expensive first-stage selector switch to each customer as in the first exchange, the customer was given access to the first-stage switch of a , often by a linefinder which searched "backward" for the calling line; so requiring only a few relays for the equipment required for each customer line.

Later Strowger (SXS) exchanges often used a subscriber uniselector as part of the line equipment individual to each line, which searched "forward" for a first selector. This was more economic for higher calling-rate domestic or business customers, and had the advantage that access to additional switches could readily be added if the traffic increased (the number of line finders serving a group of was limited by the wiring multiple installed). Hence exchanges with subscriber uni selectors were usually used at British exchanges with a high proportion of business customers e.g. director exchanges, or in New Zealand where the provision of local calling meant that residential customers had a relatively high calling rate.

The fundamental modularity of the system combined with its step-by-step (hence the alternative name) selection process and an almost unlimited potential for expansion that gives the Strowger system its technical advantage. Previous systems had all been designed for a fixed number of subscribers to be switched directly to each other in a mesh arrangement. This became quadratic ally more complex as each new customer was added, as each new customer needed a switch to connect to every other customer. In modern terminology, the previous systems were not "scalable"

Crossbar Switch: Crossbar telephone switching systems were developed by LM of Sweden in the 1930s. Ericsson switches were very popular in Europe, especially in the United Kingdom.

Western Electric (aka the Bell System) obtained licenses from Ericsson to develop their own crossbar switches. The Crossbar switch had a significant advantage over either Panel or Step by Step since it was able to use a "" concept where it would take incoming digits, store them, and then process the call. It was also able to do call routing and determine where a call should be sent to by doing "translations" of the incoming digits and deciding how to send the call.

The concept of the crossbar is the crossbar mechanism operates on a concept where dialed digits would change the position of the crossbar and connect to other parts of the matrix. It was still the same "level" concept of the step by step and panel but using more efficient and smaller equipment.

No.5A Crossbar:

Technological advancements came fast and furious after World War II. Western Electric developed an advanced crossbar switch known as the #5 Crossbar (#5XB for short). The #5 Crossbar was similar to the #1 Crossbar but an advanced design. The first installation of a #5 Crossbar was on July 11, 1948 in Media, PA. The #5 Crossbar became the “bread and butter” telephone switch of a growing nation in the 1950s and 1960s. The last #5 Crossbar was built in 1969.

The #5XB was also significant since it was the first switch to utilize (with modified originating registers) to handle customer dialed Dual Tone Multi-Frequency (DTMF, aka “Touch Tone”) dialing in the early 1962. Electronic Switching system:

In , an electronic switching system (ESS) is:

A telephone exchange based on the principles of time-division of digitized analog signals. An electronic switching system digitizes analog signals from subscriber loops, and assigns them to appropriate time slots. It may also interconnect digital data or voice circuits.

A switching system with major devices constructed of components. A semi-electronic switching system using reed relays or crossbar matrices for its talk paths, as well as semiconductor devices in , was also considered to be an ESS in the 20th century. 1ESS switch was a prominent example.

3 ESS (3ESS):

In the early 1980s, before the Bell System was broken up, the Federal Communications Commission required Bell to allow telephone subscribers equal access to any long-distance carrier they wished to use. This required extensive changes to the switch generics. The cost of modifying the 3ESS's generic (base program) to support equal access turned out to be greater than the cost of replacing all the 3ESS offices then in use. Thus the effective service life of the 3ESS was less than ten years in most cases. (In the Bell System, the service life of a telephone switch is usually between twenty and sixty years.)The 3ESS is quite a small switch. Even including the distributing frame, it can easily operate inside a semi-truck trailer.

The 3ESS's processor is the 3A CC, which stands for 3A Central Control.

Most parts of the switch are duplicated for reliability. This includes the CC (one is running, the other idle; they switch when there is a problem, or just if someone feels like it) and associated Main Store, the standby CC is made active and the active CC is made standby. When there is a problem (or when the idle CC is being maintained) it is taken Out Of Service.

Electronic Switching System TDM:

The electronic switching systems that have been deployed differ materially from the electromechanical systems. Instead of merely replacing relays, selectors, and crossbar switches of the electromechanical systems with transistors or other electronic circuitry, many new concepts have been involved. Two principal types of electronic systems, constructed and placed in service, employ a different control and transmission approach although both use similar techniques. They are designated the Time Division Multiplexing (TDM) and the space division categories. The TDM electronic switching system may be pictured as comprising a common highway over which all conversations take place. This highway is time-shared by all connecting subscriber lines and trunks through a series of high-speed electronic gates. Initial developments by Company and the Bell Telephone Laboratories utilized this method. The Automatic Electric Company's EAX and the Bell System's No. 101 ESS employed TDM by means of electronic switching. This particular type is more suitable for PBX installations and small central offices, although recent improvements have increased the capacity of the No. 101 ESS to 3,000 lines. The space division method establishes an individual path between the callings and called lines which is the basis of the Bell System's No. 1 ESS.

TDM uses a common transmission path or highway which may be compared to the frequency division method of telephone carrier systems whereby several voice channels are stacked on the same conductors. A different frequency band is used for each voice channel in this type of . In the TDM system, on the other hand, a speech signal is sampled on a repetitive basis and transmitted in a definite time sequence with respect to the samples of the other voice channels.

No. 10A Remote Switching System (10A RSS): The RSS consists on 3 main components.  The Remote terminal   The controlling ESS The remote terminal play as a extension of a host ESS as illustrated in given figure. At remote terminal a microcontroller is set and is acting on given commands.

Application Area of No.10A RSS: Application Area of following RSS is as fellow.  CDO replacement  New Wire Centers   Feature Extension Overall Working and block Diagram of RSS: Following is the Block diagram of No.10A RSS to demonstrate its working

New Development at AT&T: The networking experts at AT&T Labs enable AT&T to maintain its position as a market-share leader in high-speed access services. AT&T was one of the first in the industry to implement a fully operational, coast-to-coast IP backbone supporting OC-192 (10Gbps) transmission speeds. Following are Some new Developments of AT&T:  Intelligent Optical Network  Predictive and Proactive network management system  AT&T VPN  Voice over IP  Recent enhancements to AT&T Managed Services Portal for Hosting customers  Transport Trouble Ticket Automation  Speech Recognition and Automation Applications  Global Fault Platform (GFP)

References:  https://www.corp.att.com/attlabs/development/focus.html  http://www.research.att.com/evergreen/about_us/about_us.html?fbid=dljKDUo5 Mef  http://www.corp.att.com/attlabs/development/  http://www.corp.att.com/attlabs/development/innovative.html  http://www.att.com/smallbusiness/wireless/wirelessHome.jsp  http://www.att.com/#fbid=Gx2BGWwj0iY  http://en.wikipedia.org/wiki/List_of_telephone_switches  http://en.wikipedia.org/wiki/Telephone_exchange  http://www.maximintegrated.com/solutions/telecom_switches/