TELECOM Digest OnLine - Sorted: Re: Unlisted Phone Number

Re: Unlisted Phone Number
Sun, 25 Mar 2007 09:47:37 EDT

In a message dated 23 Mar 2007 19:45:02 -0700,

> It's also notable that much of the country, at least 11 states, were
> not as yet equipped to receive DDD calls. We forget that the
> implementation of DDD required both new equipment at the sending end
> as well as new equipment and often numbering changes at the receiving
> end. It's one thing to assign everyone a unique ten digit number
> nationwide, but quite another to convert local switchgear to
> accomodate it. It's also impressive in that the "logic" to handle
> billing records, signalling, and routing, was all done by relays.

Another requirement for incoming DDD was that trunk groups be
reinforced to provide at least P=.01 (not more than one call out of
100 would fail because of all-trunks-busy) on the final route. This
required a considerable increase in trunking capabilities in many

(An interesting artifact of this requirement, probably duplicated
in many places, was incoming calls to Blackwell, Oklahoma. You could
readily tell if your call had taken the high-usage direct trunks from
the Oklahoma City 4A or the final route via Ponca City by the set-up
time for your call. Calls over the direct trunks were XB to XB and
set up virtually instantaneously. Calls on the final route had a
noticeable delay, since Ponca City was a step office and had to send
the number to the Blackwell office by dial pulses.)

Wes Leatherock

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