Path: utzoo!attcan!uunet!lll-winken!netsys!vector!nobody From: kitty!larry@cs.buffalo.edu Newsgroups: comp.dcom.telecom Subject: Submission for comp.dcom.telecom Message-ID: Date: 9 Oct 88 17:19:24 GMT Sender: chip@vector.UUCP Lines: 53 Approved: telecom-request@vector.uucp (USENET Telecom Moderator) X-TELECOM-Digest: volume 8, issue 159, message 1 X-Submissions-To: telecom@bu-cs.bu.edu (TELECOM Digest Coordinator) X-Administrivia-To: telecom-request@vector.uucp (USENET Telecom Moderator) In article ssc-vax!clark (Roger Clark Swann) writes: > I just got through making a phone call from my office here in > Seattle to our plant in Huntsville, AL. The hardware at each end > should be a #5ESS (I am told). The routing of the call should > normally be over private, leased circuits and should NOT be going > onto the public network. It turned out that the phone I was trying > to reach in Huntsville was busy for several tries. Each time, an > audio circuit was opened and the busy signal was generated at the > far end. Now with that background, here is the my question: > Why wasn't the busy signal generated by the PBX equipment at my end? It sounds like you have some variant of Centrex service, with some type of tie line network. Whether the tie lines are "conventional", furnished by CCSA (Common Control Switching Arrangement), or part of an ETN (Electronic Tandem Network), the switching behavior using today's technology is all the same: the call is still physically completed to the far end switch. The far end switch provides the supervisory tone indications of busy, ringing or recorded intercept, and connects the call if possible. Typical busy signal "holding time" is so short (a few seconds), that there is no significant advantage in immediately dumping a tie line call and furnishing busy tone from a trunk within the near end switch. This situation may change in the future as switching systems become more sophisticated and exchange high-speed digital information prior to setting up a talk circuit - would would occur ONLY if voice connection were in fact needed. > I thought that the system did some talking over a data link before > opening the audio path anyway. If you are referring to CCIS, then the information pertains only to the dialed digits and originate/answer supervision. As far as existing CO and PABX equipment is concerned, a no-answer (i.e., ringing at the far end) and a busy condition is the same. The "audio path" is opened with virtually no delay as you complete dialing of the last digit of the access code(s)+telephone number. The far end switch is responsible for returning all supervisory tones, except when no tie trunks are available from your site or an intermediate switching center. > If so, the 'busy' should be signaled > over the data link and the local equipment would take care of it This may become commonplace in the future, but I would be extremely surprised if your organization had equipment which operated in this manner. I know that work has been done by AT&T, Northern Telcom, and Rolm with respect to more sophisticaled digital signaling protocols over a true digital data link, but the only implementations that I have seen pertain to CAS (Centralized Attendant Service). <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {att|hplabs|mtune|utzoo|uunet}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"