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 areas.(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 snipped-for-privacy@aol.com snipped-for-privacy@yahoo.com
[TELECOM Digest Editor's Note: Does anyone (mainly big-city telephone users) remember how in the early years following the Second World War how certain types of old, antiquated phone switches could not immediatly produce a 'busy signal' if the line was busy? People would call my office phone WEbster-9-4600 and the line would seemingly 'ring' once or twice in their ear, then instantly change to a busy signal. Not always, not late at night, but only during the day at busy hours, so apparently not only was my office phone busy, but so were the devices which would return 'busy signals'. PAT]