Path: utzoo!attcan!uunet!pyrdc!pyrnj!rutgers!sunybcs!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: crossing phone lines
Summary: Not a good idea...
Message-ID: <2689@kitty.UUCP>
Date: 13 Sep 88 03:46:19 GMT
References: <7921@cit-vax.Caltech.Edu>
Sender: nobody@cs.Buffalo.EDU
Organization: Recognition Research Corp., Clarence, NY
Lines: 44

In article <7921@cit-vax.Caltech.Edu>, stevel@tybalt.caltech.edu (Steve Ludtke) writes:
> A friend just presented me with an interesting question. He has an answering
> machine, and 2 phone lines. He wanted to know if he could just cross the
> two lines to get it to work on both. My immediate response was, of course
> not, that would really screw thing up. However the longer I thought about
> it the less certain I became. Since he wouldn't be dialing out while it was
> hooked up like this, that wouldn't be a problem. I don't know what a phone
> line will do if you send a ring signal over it. Anyone have any theories.

	In the on-hook (i.e., idle) state, connecting the two lines exactly
in parallel (tip1-to-tip2 and ring1-to-ring2) will, in general, be undetected
by the central office apparatus since there will be no current flow.
	In the on-hook state, connecting the two lines in parallel with
reversed polarity (tip1-to-ring2 and ring1-to-tip2) is _guaranteed_ to
create an off-hook condition for BOTH lines, rendering both lines
inoperable for both incoming and outgoing calls (i.e., a permanent signal
is created in the CO, along with an eventual trouble report).
	In the on-hook state with both lines connected in parallel, an
incoming call will result in an immediate ring trip, resulting in no
effective ringing signal to any customer apparatus.  In most CO's the
ring trip will momentarily pull dial tone on the other line, but then
disconnect the incoming call.  In some CO's both lines may be forced
into a permanent signal - even though the incoming call has been terminated.
In some ESS offices, an automatic trouble report may be generated -
even if both lines do not lock up as a permanent signal.
	In the off-hook state with both lines connected in parallel, an
outgoing call attempt will result in both lines pulling dial tone as a
near-simultaneous event.  Either rotary or DTMF dialing will most likely
succeed in two near-simultaneous calls to the same number.  If the
CO traffic load is high (especially in an electromechanical office),
resulting in one line being connected to a dial register more than a
hundred milliseconds before the second line, chances are that a spurious
rotary dial pulse will be created - thereby rendering effective dialing
impossible on one or both lines.

> I'm tempted to just try it, and see what happens.

	Try it if you like, but I can assure you that no useful result
will occur.

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
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