larry@uunet.uu.net (Larry Lippman) (04/01/91)
In article <telecom11.253.8@eecs.nwu.edu> rees@pisa.citi.umich.edu (Jim Rees) writes: > > Using polarity-dependent superimposed > > ringing, four unique parties could be signaled. Eight-party lines > > used coded ringing, and could be dialed directly since there were SxS > > connectors arranged for automatic coded ringing selection. > I don't know what our old (Bell System) switch was before it was > replaced with a 1A some time in the late '70s, but it had ringback on > 491x. Different values of 'x' would give eight different coded rings > plus continuous ring. I miss this feature. Our current switch > doesn't even have a ringback number that I can find (I've tried all > the test prefixes, and located all kinds of tones, battery, > terminated-no-battery, and so on, but no ringback). I feel certain that your CO has a ringback number; it may well be "hidden" as a three or four digit number, rather than a seven-digit test line number, however. Ringing another party on the same party line is a unique case called "revertive calling". Such a call cannot be completed using the conventional SxS connector. It was accomplished using apparatus known as a reverting call selector. While there was more than one way to implement revertive calling in a SxS office, a typical method was to dial four digits such as NNYD, where NN is a two-digit access prefix common to the CO, Y is your party code number and D is the party code number of the destination station. After dialing the appropriate four-digit number above and hearing an acknowledgement tone, your handset was placed on hook. Your telephone then rang along with that of the destination party. When the ringing stopped it indicated that the other party had answered and you picked up your handset. To abandon an unanswered call required momentarily picking up your handset. Implementing revertive calling the *right* way was a little tricky from a circuit design standpoint, since your ringing code is *not* the same as that of the called party! How could your telephone ring to indicate that the called party was being rung with a different electrical and/or cadence code? This is why in a better reverting call implementation, two digits were dialed: your ringing code and that of the called party. What really happened is the the ringing cycle was split. During your silent interval the ringing condition for the other party was placed on the line; during their silent interval your ringing condition was placed on the line. If your ringing was electrically the same condition but with different cadence for the other party, you simply heard their cadence and the ringing cycle was not split. Less sophisticated reverting call selectors did not ring your telephone at all. You dialed an access code followed by the party code of the called party. You heard an acknowledgement tone and hung up. After you *think* the other party has had time to answer the telephone, you then picked up the line. If they were there, fine; if not enough time or they picked up and heard silence and then hung up -- tough. In some ESS CO's where party lines were almost non-existent, *no* reverting call trunks were installed at all. If you wanted to call another party on your party line, you were required to go through the operator. Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" VOICE: 716/688-1231 {boulder, rutgers, watmath}!ub!kitty!larry FAX: 716/741-9635 [note: ub=acsu.buffalo.edu] uunet!/ \aerion!larry