Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!decwrl!sun-barr!newstop!texsun!texbell!vector!telecom-gateway From: csense!bote@uunet.uu.net (John Boteler) Newsgroups: comp.dcom.telecom Subject: Audible Ringback vs. Ring Plant Message-ID: Date: 17 Jul 89 11:12:39 GMT Sender: news@vector.Dallas.TX.US Lines: 52 Approved: telecom-request@vector.dallas.tx.us X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@vector.dallas.tx.us X-TELECOM-Digest: volume 9, issue 243, message 1 of 9 The audible ringback heard when an outgoing call is placed has, in the past, always been generated by the distant office. Not so with ISDN and SS7, anymore. But, for simplicity, let us stick with the here and now. Office Tone Plant ------ ---------- Stepper in phase(when it feels good) XBar1 in phase XBar5 in phase ESS1 not in phase ESS5 not in phase DMS100 not in phase Rolm PBX lucky to get anything! Where 'in phase' indicates the audible ringback tone plant is always in phase with the ring plant; when you hear ringback signal, the distant phone is ringing at the same instant. 'Out of phase' means that the distant ring plant may or may not be in phase with the audible ringback--there are no guarantees here. Steppers sent the same Holzer-Cabot ring plant back to you as they sent to the called phone, hence you KNEW they were in phase. #1 and #5 crossbars had tone plant for signalling and a separate ring plant for ringing called phones (#1s sounded neater). ESS changed all this, probably to distribute the load over the tone plant more evenly. It was not an infrequent occurrence on a stepper that the dial tone frequency would sag for a few seconds when too many people requested dial tone simultaneously :> In any case, the ring cycle calls for 2 seconds of plant interspersed with 4 seconds of pause. Consider the following scenario: a caller places a local call (to eliminate the vagaries of the long distance network for the moment). The instant the distant office connects, it places ring plant on the line, ringing the distant phone--2 seconds. Then two seconds of pause, and the audible ringback begins for 2 seconds. Immediately after the audible ringback ends, the ring plant begins on the distant end again. Now, no matter how many rings one extrapolates to from here on out, if the caller hangs up after X rings the distant phone will have rung X+1 times. Graphically: <2 sec> Local -------|-------|-------|-------|-------|-------|-------| XringXX XringXX... Distant -------|-------|-------|-------|-------|-------|-------| XringXX XringXX XringXX... These time pieces may appear in any of the finite phase relationships above to yield any number of confusing situations to those who don't know of them. Applications are left to the reader.