ANdrew 8-8000

[Sid Schweiger]

>>IIRC, the 931 exchange was designed to moderate "contest" & "talk" 
traffic by only allowing a small number of calls from each exchange/area 
code (don't remember which) giving a busy to the rest of the callers.  
It was to avoid clogging up tie lines from one exchange to another.<<

The 617-931 exchange (and other similar exchanges in every major city) is known as a "choke" exchange.  It is specifically designed to prevent overloads and cable and circuit burnouts (which used to occasionally happen) by routing excess calls to dead or non-existent trunks.

The one example I can think of, which led to the invention of this type of configuration, was the old WABC offering two tickets to a Beatles concert, using a phone number in the midtown-Manhattan LT1 exchange which carried most of the phone service for ABC's New York operations.  The ensuing overload resulted in a cutoff of emergency police/fire/ambulance service calls to the central dispatcher in Manhattan from Brooklyn, Queens and Staten Island.  The story goes that telco executives paid a call to ABC's executive suite and threatened a total service cut-off and equipment removal if they ever tried anything like that again.  Meanwhile their technical types came up with the choke system, to avoid the problem in the future.

Sid Schweiger
IT Manager, Entercom New England
20 Guest St / 3d Floor
Brighton MA  02135-2040