TELECOM Digest OnLine - Sorted: Re: Non-Bell ESS?

Re: Non-Bell ESS?

Diamond Dave (
Wed, 06 Jul 2005 21:11:46 -0400

On 6 Jul 2005 10:59:05 -0700, wrote:

> The Bell System put its first test call through a laboratory
> Electronic Switching System in 1958 and had a prototype system in
> public service in the early 1960s.

> Would anyone know when other telephone companies, either in the
> U.S. or abroad, developed and implemented their own ESS? For
> instance, when did Automatic Electric put one in service?

Automatic Electric made the #1 EAX (invented in 1973 or 1974) and
later in the 1970s, the #2 EAX. These were WECo #1ESS/1AESS like in
nature -- analog switch with computer control. These were originally
just for a Class 5 end offices but later models could handle Class 4
tandem functions.

Automatic Electric later made the GTD-3 (or #3 EAX ) and GTD-5 (or #5
EAX) in the 1980s. These are full digital switches. A number of #5 EAX
switches are still in service, though as time goes on they're being
replaced with other switch types.

Stromberg-Carlson had their ESC (Electornic Switch Control?) switch in
the 1970s. This switch was analog with computer control. In the 1980s,
they made the DCO (Digital Central Office). The DCO is now made by a
division of Siemens known as Stromberg/Siemens.

Northern Telecom (now Nortel) invented the DMS-10 in the late 1977 and
in 1979 the DMS-100 switch (followed by other DMS switches, used as
tandems, operator services platforms, or international gateways).
Supposedly Northern Telecom had an electronic PBX (the SL-1) around

But Vidar was the first fully digital local end office switch,
invented circa 1976. I don't think there are any Vidar (later
TRW-Vidar) switches still in service.

WECo was behind the curve on this one. Though they invented the fully
digital long-haul #4ESS tandem in 1976, they didn't have a full
digital end office until they invented the #5ESS in 1982.

Dave Perrussel
Webmaster - Telephone World

[TELECOM Digest Editor's Note: I know from my personal experience that
Illinois Bell had ESS in the Wabash office in downtown Chicago in
1974, along with the Superior office on the near north side the same
year. But I think they were just the first editions or versions of
that type of switch. PAT]

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