The GTD-5 EAX first appeared in Banning, California on June 26, 1982,[1] slowly replacing the electromechanical systems still in use in the independent switch market at that time.
The GTD-5 EAX was also exported internationally, and manufactured outside of the U.S. under license, primarily in Canada, Belgium and Italy.
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.
Physically, this distinction made little sense, but was important from a software compilation standpoint.
Since the APC and TPC processors shared a large memory-mapped space, some stages of compilation were performed in common.
Unlike the SM in the competitive 5ESS Switch, the TCUs did not perform all call processing functions, but limited themselves to digit collection and signalling interpretation.
The RLU was a condensed version of the RSU, with no local switching capability and limited line capacity.
When integrated with the GTD-5 EAX, it used a custom software load that permitted message communication with the remainder of the system.
The APC, TPC, and TCUs all connected to a smaller shared memory, the Message Distribution Circuit (MDC).
This was an 8k word 96 port memory that was used to place small packetized messages into software defined queues.
Communication between processors and peripherals was memory mapped, with similar cables extending 18 bit address and data buses between frames.
A later generation expanded the number of ALUs to twelve or sixteen, as appropriate, giving larger effective concentration.
The span interface circuits were completely redundant, and all control circuitry operated in lockstep between the two copies.
This arrangement provided for excellent failure detection but was plagued by design flaws in the earliest versions.
The later generation Extended Digital Trunk Unit (EDT) included 8 T-carriers per card, and incorporated ESF and PRI interfaces.
The active processor always kept memory up-to-date so that when these forced switches occurred, little data loss was suffered.
[4][5] This Pascal was extended to include a separate data and type compilation phase, known as the COMPOOL (Communications Pool).