Gkar:

Beg to differ with you there. 1A2 equipment which dates way back to the early sixties had option straps on the CO line cards to select the length of the supervisory disconnect signal.

Mechanical CO switches (Panel, SXS, Crossbar, etc.) always had supervisory signaling to drop a "cord board's" mechanical hold circuits. This was in an effort to reduce the number of trunks required into a customer's PBX (cord board).

Electronic switches (ESS, DMS, ESWD, etc.) were developed later when the end-user equipment could not be guaranteed to be made by the same manufacturer. In the late sixties, it became legal to buy key systems and PBX's from manufacurers other than the phone company's CO switch manufacturer. The telephone companies had to provide the necessary compatibility with regard to signaling.

Just to play it safe, when the electronic switches were developed, the manufacturers set the supervisory disconnect signal "just a little bit longer" so that their signal worked with the new slew of customer-owned systems from all over the world.

Back to 1A2; the settings (a physical wire strap) were "short" for crossbar offices and "long" for ESS. Loop supervision has been a major part of the POTS line business for decades. I am not sure where you got your information, but it's not accurate by any stretch of the imagination.

------------------
Ed
---------
How come there's always enough time to go back and fix it a second time?

Ed Vaughn, MBSWWYPBX