GTD-5 EAX

The GTD-5 EAX (General Telephone Digital Number 5 Electronic Automatic Exchange) is the Class 5 telephone switch developed by GTE Automatic Electric Laboratories. This digital central office telephone circuit switching system is used in the former GTE service areas and by many smaller telecommunications service providers.

The GTD-5 EAX first appeared in Banning, California on June 26, 1982, slowly replacing the electromechanical systems still in use in the independent switch market at that time. The GTD-5 EAX was also used as a Class 4 telephone switch or as a mixed Class 4/5 in markets too small for a GTD-3 EAX or 4ESS switch. The GTD-5 EAX was also exported internationally, and manufactured outside of the U.S. under license, primarily in Canada, Belgium and Italy. By 1988, it had 4% of the worldwide switching market, with an installed base of 11,000,000 subscriber lines. GTE Automatic Electric Laboratories became GTE Network Systems and later GTE Communication Systems. In 1989, GTE sold partial ownership of its switching division to AT&T, forming AG Communication Systems. AG Communication Systems eventually fell under the ownership of Lucent Technologies, and was dissolved as a separate corporate entity in 2003.

The processing building block of the GTD-5 EAX was the "processor complex". These were each assigned a specific function within the overall switch design. In the original generation, Intel 8086 processors were used. These were replaced by NEC V30s (an 80186 instruction set compatible processor with 8086 pinout implemented in CMOS and somewhat faster than the 8086 due to internal improvements) in the second generation, and ultimately by 80386 processors.

The APC was responsible for the craft interface to the system, administration of status control for all hardware devices, Recent Change, billing, and overall administration.

The TPC was responsible for call sequence and state control. It received signalling inputs collected from peripheral processors (see MXU, RLU, RSU, and TCU below) and sent control information back to the peripheral processors.

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