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Posted by on April 14, 2008, 12:50 pm
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> With all due respect, Bell/W.E. did not design
> SxS. That was done by, or at the behest of, a Kansas
> City undertaker named Strowger, as I recall.
According to the history, the early SxS out there had limitations and
Bell felt it was a comedown from manual service. When Bell adopted
SxS it made numerous improvements to the AE design. However, for many
years it had Automatic Electric build SxS for it under contract.
SxS was cheap and rugged. It's big limitation was not being able to
expand easily and economically to large networks since it was limited
to the ten positions on the switch, which is why common control Panel
was developed early on for city use. But SxS was great for small
cities and towns and was used extensively.
Indeed, into the 1960s the Bell System found that common control was
just too expensive to be justified in many SxS locations. It took
time to get the cost of electronics and overhead down to replace a SxS
office with ESS. I think small version crossbar never proved
economical. While plenty of suburban areas were growing and were
candidates for No 5 crossbar, others were stagnate and did just fine
for SxS. Modest growth was easily accomodated by adding more
selectors, certainly cheaper than replacing the whole office.
A major product was the Communiity Dial Office (code 357?) which
served just a few hundred lines. I think these offices were
essentially a crude form of a concentrator, and probably were replaced
by such a device.
I think when my town went dial, it only had about 500 lines although
considerable growth was expected with new 1950s developments; and
probably doubled to 1,000 after dial went in. Probably a similar
experience in many towns.
Ironically, SxS adapted well to Centrex service where Panel could not.
> When the first dial office was established in
> Oklahoma City, in 1920, it had to come from Automatic
> Electric, since there was none from Bell/W.E.
>
> Some of it was still is service into the 1950s
> and I think probably another 10 years or so late.
Step by step reached its peak--in terms of raw lines served--in 1974.
It's _percentage_ was declining as crossbar and ESS replaced it, but
it was a still the backbone of the Bell System in 1974.
The Bell Labs Record of the 1970s is filled with articles about
electronic front ends and back ends to augment SxS. Some of this was
for Touch Tone, some for DDD, some for more efficient routing in the
office.
SxS was more maintenance intensive, though a relatively simpler design
than a crossbar unit. Springs and such need periodic adjustments.
Neglect of maintenance contributed to the 1970s service crises; such
as when in one office they let the Line Finders go and that meant it
got very hard to get a dial tone.
| ![Re: Origin of SxS [Telecom]](/images/header.jpg)
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