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Electronic Switching Is 'In'.

Electronic switching was one of the ten tremendous developments of Communications News' first decade and the promise of electronic switching has been fulfilled during the past decade as the pushbutton telephone, the digital PBX, and digital facsimile and high-speed data transmission over telephone lines have become not only possible but commonplace.

During CN's very first year the first electronic switching office went into commercial service at Succasunna, New Jersey, on May 30, 1965, and "Number One ESS" proved to be a pivotal point in telephone switching history.

That event was the result of a formal Bell Laboratories' effort begun at the end of World War II. The goal was to apply electronics to switching, and bring customers the speed, flexibility, and reliability offered by electronic components. Laboratory domonstration systems developed by the late 1940s relied on electronic tubes for logic, memory, and control functions. These systems greatly encouraged Bell engineers, but also pointed up the need for more economical logic and memory devices. The solid-state revolution, sparked by Bell Labs' invention of the transistor (see story, page 84), provided the breakthrough switching engineers needed. Developments then came rapidly, but the concept had to be tested and retested many times to make sure the new switching systems would meet the service standards Bell subscribers had come to expect. A customer trial from 1960 to 1962 in Morris, Illinois, proved electronic systems could do the job. The system used in Morris contained about 4,000 electronic tubes, and 12,000 transistors.

Two basic types of ESS were developed: the two-wire office used for commercial Bell system service, and the four-wire office used for the government's AUTOVON network. The first ESS in the AUTOVON network began operation in May 1966.

In the early 1960s GTE Automatic Electric was also active on the electronic switching front. A test model of its "Number One EAX" (Electronic Automatic Exchange) was operational in 1962. An initial installation of EAX equipment with a capacity of 600 lines was installed in the Portage, Indiana, exchange of General Telephone Company of Indiana, beginning in 1963, for a field trial.

GTE Automatic's Number One EAX was a common control telephone switching system that met the requirements for a medium to large and office and a combined end and toll office. Switching was accomplished by means of a 2-wire, space-divided, read network, driven by a stored program, with electronic common control.

The first Number One EAX developed by GTE-Automatic Electric was cut into service in July 1972, at St. Petersburg, Florida. A second was cut into service at Erie, Pennsylvania, in January 1973.

Another early electronic switching system was the NX-IE developed by North Electric Company . . . an electronically controlled crossbar switching system.

In early 1969, Northern Electric Laboratories announced the SP-1 electronic switching system, with a field trial taking place in Ottawa, Ontario. The system was cut over in 1970. The SP-1 was feasible in the central-office role for as few as 2000 lines, yet could grow to 20,000 lines or more. The first fully operational office was installed in Alymer, Quebec, in 1971.

SP-1 is an electronically controlled switching system using the "Minibar" miniature crossbar switching matrix. The central control complex consisted of a duplicated electronic data processor, a program store, and a call store. The program store utilized an nondestructive readout memory known as the piggyback twistor, whereas the call store consisted of ferrite sheets. The SP-1 used several discrete wired logic electronic units such as markers and receiver-senders as peripheral equipment. It could be used on a two-wire basis as a local switching system or on a four-wire basis as a toll switching system.

By March 1973, Northern Electric had some 51 orders for the SL-1 and the electronic switching race was on!

Meanwhile, the Bell System continued to expand and improve its electronic switching systems.

The first Number Two ESS, manufactured at the Western Electric Company Hawthorne Works in Chicago, went into operation in late 1970 in Oswego, Illinois. It was developed at Bell Labs for use in medium-sized central offices serving from 1000 to 15,000 lines and it offered a variety of custom calling services available to customers, such as speed calling, call forwarding, three-way calling, and call waiting. It has a ferreed network, permanent-magnet twistor, semipermanent memory, and a ferrite-sheet call store.

Bell's Number Four ESS, developed in 1972, was designed primarily as a successor to electro-mechanical 4A crossbar systems. The 4 ESS was a high-capacity, versatile toll and tanden switching machine for the long-distance telecommunications network which could handle at least 350,000 long-distance calls per hour . . . about three times as many as the electromechanical system. It was the first large machine in the Bell System to switch digital signals directly.

When Communications News celebrated its tenth birthday in 1974, the Bell system had just installed its 500th Number One ESS in Springfield, Illinois and new ESS offices were being installed across the nation at a rate of one every two working days!

Today, a decade later, we are talking about "Number 5 ESS . . . and those early systems have their limitations. J. L. Johnson, manager of product planning for AT&T digital switching equipment, points out that the 1 ESS and two other ESS systems developed since 1965, offer custom-calling services such as speed calling, all forwarding, three-way calling and call waiting. He explains that with a continuing program of updating, the three ESS systems--1 ESS, 2 ESS and 3 ESS--offer services required by business customers and, increasingly, by residential customers. "On the other hand," he adds, "those three older ESS systems have a shortcoming for a community like Morris County. All were designed for specific numbers of customers. The 1 ESS was intended for metropolitan use to serve 10,000 to 65,000 lines, the 2 ESS was developed for smaller communities requiring 4,000 to 25,000 lines, and the 3 ESS with capacity of 600 to 4,500 lines, was intended for small towns and rural communities. Once capacity is reached for any of them, growth can be accommodated only with a completely separate central system."

The 5ESS switching system . . . with its remote switching modules and the SLC-96 terminals . . . was designed by AT&T Bell Laboratories to meet changing customer needs. It brings digitally based information services closer to the home and office, and serves up to 100,000 customers in communities scattered

over more than 100,000 square miles.

This flexibility was made posssible by designing the system as a collection of semi-independent switches administered as one interconnected switching center. The central processor is the AT&T 3B2OD computer, and each module is equipped with its own microprocessor and software.

AT&T's 5ESS switch has been adding new system features with almost every recent installation. some highlights include: the first multimodule 5ESS switch allowing easy growth and special custom residence services installed in Sugar Grove, Illinois, in August, 1983; the first 5ESS switch with local/toll switching capability installed in Bradford, Pennsylvania, in October, 1983; the first 5ESS switch incorporating the new space-saving, six-foot-high cabinets in Pinnacle Peak, Arizona in February 1984; and the first "Hot Slide" (moving an operating switch into an old office to eliminate the need for a new building) of a 5ESS switch, installed in June, 1984, in Jackson, Mississippi.

Advances in electronics and computer software are giving telephone companies more options in meeting customers' needs, and giving telephone users greater control of the calls they make and receive.

When you install a digital switching system, you're not only modernizing the switch, but your interoffice facilities and loop plant as well. An integrated 5 ESS digital switch, for example, provides the economic opportunity to bring the antiquated loop plant into the modern technology world.

The RSM (Remote Switching Module) can be located up to about 100 miles from its host 5 ESS switch and can be used to serve communities with less than 4,000 telephone lines. This capability makes the RSM suitable as a small community dial office in a rural or suburban setting while providing the same features and services of a major communications center.

"The new services were made possible by the continued development and proliferation of electronic switching systems that are controlled by computer instructions that can be changed to meet the individual needs of telephone companies and their customers," says AT&T's Bob Carlson, adding, "In addition to being able to trace nuisance calls, customers can program their local switching system to have certain pre-selected callers automatically transferred to another telephone; arrange to have certain callers announced by a distinctive ring or call-waiting tone; or be called back automatically when a busy line they have called becomes free. For the telephone customer who always seems to reach the phone just after the last ring, there's also a solution: At a signal, the telephone will automatically dial the last number that called it."

Electronic switching has totally changed the telephone industry!
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Copyright 1984 Gale, Cengage Learning. All rights reserved.

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Publication:Communications News
Date:Sep 1, 1984
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