bote@uunet.uu.net (John Boteler) (07/17/89)
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.dupuy@cs.columbia.edu (Alexander Dupuy) (07/31/89)
In article <telecom-v09i0243m01@vector.dallas.tx.us> John Boteler writes:
Office Tone Plant
------ ----------
Rolm PBX lucky to get anything!
Actually, with Rolm PBX's anything means just that! We have one of these
monsters at Columbia now, and it has happened that someone calling me got a
busy signal which changed to a ringback after I hung up on the previous call!
What I'm curious to know is whether called party answer supervision works
correctly in these cases, i.e. if someone calling long distance were to get a
busy and hang on the line until I hung up on the previous call, would they only
be billed after I had answered (assuming they were using an LD carrier which
could detect answer supervision)?
@alex
inet: dupuy@cs.columbia.edu
uucp: ...!rutgers!cs.columbia.edu!dupuygoldstein@delni.dec.com (08/02/89)
In article <telecom-v09i0268m09@vector.dallas.tx.us>, dupuy@cs.columbia.edu (Alexander Dupuy) writes... >In article <telecom-v09i0243m01@vector.dallas.tx.us> John Boteler writes: > Office Tone Plant > ------ ---------- > Rolm PBX lucky to get anything! > >Actually, with Rolm PBX's anything means just that! We have one of these >monsters at Columbia now, and it has happened that someone calling me got a >busy signal which changed to a ringback after I hung up on the previous call! While I work for a company that's the largest competitor to Rolm's parent company (until the sale of Rolm to Siemens goes through...), I still don't like to see gratuitous Rolm-bashing. I spent quite a long time specializing in the care and feeding of Rolm switches (as a large customer) and while they certainly aren't perfect, they're generally predictable once you know the score. In the case above, Alexander Dupuy is reporting on "autopark", one of the nicest Rolm features that never caught on elsewhere! Autopark allows a caller to dial in to a DID extension and, if the line is busy, hear a PBX-generated busy signal. This is not supervised, so it's free. BUT if the caller knows about this feature, and listens to it long enough (the default is 10 seconds), then (if I remember) the busy signal is replaced by "music on hold" (still free) and the called party gets a call waiting tone. When the called party hangs up, the call rings through. Supervision occurs when it's answered. This is legal because PBXs are allowed to provide audible signaling to a DID caller without returning supervision; supervision is required only when a two-way path is opened. It should, however, be obvious that PBX manufacturers affiliated with long distance carriers (be they AT&T or Bell Canada) would not be particularly anxious to implement this feature! It's one of the widest loopholes in the supervision rules. Kudos to Rolm for taking advantage of it. (It's been around for over a decade.) Of course, not many end-users even know about it. Like many Rolm features, it's a bit hard to explain.
john@apple.com (John Higdon) (08/04/89)
In article <telecom-v09i0270m08@vector.dallas.tx.us>, goldstein@delni.dec.com writes: > Of course, not many end-users even know about it. Like many Rolm > features, it's a bit hard to explain. And, like many Rolm features, it's totally screwy and totally non-intuitive. Instead of ten seconds of busy and then music, how about two seconds of busy. NO ONE listens to a busy signal for ten seconds. Having replaced many Rolms in my day, I can say that the reason their owners were quite happy to see them go was that they were so hard to use. Oh, yes, they were feature-laden. Features that required a detailed manual to describe. F'rinstance, to transfer a call in 99% of PBX switches on a single-line phone, you flash the hookswitch, dial the destination number and hang up. With Rolm, you flash, dial a code (different depending on the type of transfer), dial the number and hang up. Rolm's attitude was "We're king of the hill, and you will do it our way." For this reason, many of Rolm's features were never used by their customers. They didn't know how. And it was generally too much trouble. Yes, Rolm, it is possible to have features that work and are easy to use. -- John Higdon | P. O. Box 7648 | +1 408 723 1395 john@zygot.uucp | San Jose, CA 95150 | M o o !
dave@rutgers.edu (Dave Levenson) (08/06/89)
In article <telecom-v09i0270m08@vector.dallas.tx.us>, goldstein@delni.dec.com writes: ...commentary describing ROLM auto-park where incoming calls to busy stations get put on hold without answer supervision while queued... > This is legal because PBXs are allowed to provide audible signaling to a > DID caller without returning supervision; supervision is required only > when a two-way path is opened. It should, however, be obvious that PBX > manufacturers affiliated with long distance carriers (be they AT&T or > Bell Canada) would not be particularly anxious to implement this > feature! > > It's one of the widest loopholes in the supervision rules. Kudos to > Rolm for taking advantage of it. (It's been around for over a decade.) > Of course, not many end-users even know about it. Like many Rolm > features, it's a bit hard to explain. The trouble with this arrangement, if implemented and used by vast numbers of telephone users all over the network, is that I might call you and get autoparked because you are busy -- perhaps calling me, and being autoparked because I'm busy...etc. Or perhaps we're not calling each other, but we're each calling someone else who is calling someone else... The problem is that after a while, the network is blocked with non-revenue calls autoparked at the destination, and no new calls get through. Hopefully, someone somewhere will give up, abandon their outgoing call, and start to break up the logjam. The right solution to the waiting-for-busy problem is network-implemented automatic call back. That probably won't happen while the "network" is a disjoint set of networks owned by different carriers. Who pays for all of this "non-revenue" use of the networks? You guessed it! I suggest that the rules for supervision not permit this sort of thing. In the long run, it will only be destructive to the blocking probability or network usage cost. If ROLM wanted to be like other premises switching systems, they'd offer ACD, instead. -- Dave Levenson Voice: (201) 647 0900 Westmark, Inc. Internet: dave@westmark.uu.net Warren, NJ, USA UUCP: {uunet | rutgers | att}!westmark!dave [The Man in the Mooney] AT&T Mail: !westmark!dave