In effect, you have two questions: (1) Call supervision between PABX and Central Office
(2) Methodology used in PABX for accounting. The answer to question (1) is not easy but answerable. In effect, it has been answered in two places, the handiest is ANSI/EIA/TIA-464, Private Branch Exchange Switching Equipment for Voiceband Applications. It describes the different interfaces that conceivably could be used. The USA and Canada had many, many telephone companies doing their own thing. That has been whittled down to a manageable number of practices. You may run into anyone of them, as described in the standard. Therer is a second source of Standards on the interfaces from Committee T1. They have a series of standards that describe Interfaces between Customer Installations and the PSTN. There you'll find each interface in a separate standard, such as "Loop-start, Ground-start, Reverse Battery, DS-1, DS3 and such. The answer to question (2) is more problematic in that different manufacturers use different techniques to provide that service in their PBXs. In to-day's digital PBXs there is an added complication in that the owner of the PBX (the Hotel) may have special deals with different long-distance carriers for "least-cost-routing" of calls out of the PBX. It is possible that the interface to Carrier 1, for calls to the North East, is not the same as the interface to Carrier 2, for call to the South West. This is a very specialized area of expertise and the subject does not lend itself well to a quick explanation over TREG. Most of those experts work for the big PABX manufacturers or large consulting firms. The PABX Standard can be ordered from Global Engineering Documents in Denver, Washington, St. louis, Irvine CA, Sydney Aus, Mexico City, Miami, Paris, Hong kong, Tel Aviv or Munich. Let me know what is closest for you and I'll get you the address. I believe that ANSI sells the Committee T1 standards these days, but am not sure. Ciao, Vic
