TELECOM Digest OnLine - Sorted: Re: What Tandem in Telcom Means?

Re: What Tandem in Telcom Means?
Wed, 22 Dec 2004 09:26:26 EST

In a message dated Wed, 22 Dec 2004 03:49:19 GMT, John McHarry
<> writes:

> On Tue, 21 Dec 2004 18:31:01 -0500, Jack wrote:

>> I am new to telcom. I came across the term Tandem many times (eg. LEC
>> Access Tandem).

>> What exactly does Tandem mean?

> PAT's reference is correct, but, in the meantime, a tandem office is a
> telephone switching machine that stands between two end offices, the
> latter serving subscriber lines. In the olden days, a couple decades
> ago or less, end offices couldn't handle long distance accounting and were
> connected with toll tandems that could. In very large cities there were
> also, as I recall, some inter local tandems that allowed hub and spoke
> arrangements of local switching.

Aw, c'mon folks. Manual tandems existed before there were dial
offices, and a concern in big cities was the delay as in some cases
phone numbers had to be passed manually from the originating operator
to a tandem operator, then another tandem operator, and finally to the
terminating office.

The first dial offices to get DDD ("long distance accounting") were
end offices, and it was only later that tandems with CAMA
("Centralized Automatic Message Accounting") were used to provide
customer toll dialing to end offices not equipped for any kind of
accounting, such as step-by-step offices.

In the late 1940s I made a call from a coin box in Los Angeles, and
the operator had to go to rate-and-route to learn which (manual) toll
tandem to plug into which had trunks toward the destination. L.A. had
so many outgoing manual toll trunks that they had to be distributed
among various tandems; as I recall, for my call the operator was
director to (manual) toll tandem No. 4. which had trunks for the MX
(multi-switch) routing to the destination.

Wes Leatherock

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