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From: forrette@sim.berkeley.edu (Steve Forrette)
Newsgroups: comp.dcom.telecom
Subject: Answer Supervision on a POTS Line (Kind of)
Message-ID: <9782@accuvax.nwu.edu>
Date: 16 Jul 90 05:09:19 GMT
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X-Telecom-Digest: Volume 10, Issue 488, Message 4 of 9


Occasionally someone mentions in the Digest about how the telcos
refuse to return answer supervision to the originating party.  I've
discovered something that some of you no doubt are already aware of,
but many of you may not know:

If you have three-way calling, you can determine when the call
supervises.  This is a result of a flash not breaking to a second dial
tone until the call supervises.  For example, let's say I call a
certain number.  At any time before the person answers, if I flash the
line, nothing happens.  As soon as the person answers, a flash will
obtain the secondary dialtone.  At least this is what happens on the
1AESS I'm on.  If the call never supervises (no answer, "out of
service" recording, etc.), a flash will never obtain secondary
dialtone.  This seems to work whether the call is local or long
distance, although the propagation delay of the supervision back to my
originating office is of course longer when calling inter-state.

A couple of notes: If you flash after the last digit is dialed, but
before the 1st audible "click", the call terminates, and you get a
"fresh" dialtone.  And, if you call a number on the same switch, there
is no period where a flash will be ignored.  The call in progress will
be terminated if you flash before supervision, or you will get
secondary dialtone if you flash after supervision.

A couple of questions for you experts:  Does this only happen on a 1AESS?  
Which other switches?

Also, what are the "official" minimum and maximum on-hook durations
for a flash?  Of course, everyone I've tried to ask at Pacific Bell
doesn't even understand the question.  It's the typical routine -
"Sir, I don't understand what you're asking me, and I won't connect
you with someone that does.  Now how can I help you?"