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Information and pictures on modern Automatic Electric / AGES electronic and digital central office switching systems

AE Electronic Analog Switching Systems

Automatic Electric (by this time, a divsion of GTE) attempted to compete with Western Electric by developing their own electronically controlled analog telephone switching system. In 1972, AE released the #1 EAX  (Electronic Automatic eXchange) switch for Class 5 (local end office) functions, with Class 4 (toll) functions being added a year or so later. The #2 EAX switch came several years later to serve smaller central offices and used updated hardware and software.

AE / AGES Digital Switching Systems

Again, in an attempt to compete, Automatic Electric developed a series of fully digital central office switches. In 1978, AE started the manufacture of the GTD-3 (#3 EAX - Electronic Automatic eXchange) switch, and was succeeded by the GTD-5 (#5 EAX) in 1982.

In 1989, GTE and AT&T formed AG Communications Systems (the "AG" stood for AT&T and GTE, who co-owned AGCS). AGCS continued the manufacture and the support of the GTD-5 switch. When AT&T spun off Lucent in 1996, AT&T's interest in AGCS was transferred to Lucent.

With formation of Verizon from GTE and Bell Atlantic in 2000, GTE spun off their interest in AGCS to Lucent. To this day Lucent Technologies still supports and manufactures the GTD-5 switch.

A plug-in card for a GTD-5 switch

 Host & Remote Switching

Like their Western Electric (Lucent) and Northern Telecom (Nortel) counterparts, the GTD-5 supports host and remote switching arrangements. 


  • LBU (Large Base Unit): 2,000 to 145,000 lines and can be used for Class 4 (toll) service.

  • SBU (Small Base Unit): 500 to 20,000 lines. No toll service (cannot be used as a tandem)


  • RSU (Remote Switching Unit): Small switching system meant to replace small community dial offices with a capacity for up to 3,000 lines. A total of 32 RSUs can be supported by one host GTD-5 switch. 

  • RLU (Remote Line Unit): A large multiplexing concentrating system with a capacity of 768 lines.

  • MU (Multiplexing Unit): Multiplexes up to 96 lines.

GTD-5 switches, as one would expect, were in widespread use as GTE central office switches. They were also used in some independent telephone companies. However, as time goes on, many GTD-5 switches are being replaced with other brands and models of digital switching equipment.

More details (off-site links)

Wikipedia List of Telephone Switches

Other Modern Telephone Switching System Pages

Telephone Switching Systems - Main Page
Overview of Modern ( Electronic & Digital Switching) Systems
Automatic Electric Modern Switching Systems
Northern Telecom (Nortel) Modern Switching Systems
TRW-Vidar Switching Systems
Western Electric Modern Switching Systems
Other Modern Switching Systems of Note

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Page last modified December 20, 2008
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