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Path: utzoo!linus!gatech!ulysses!smb
From: smb@ulysses.UUCP (Steven Bellovin)
Newsgroups: net.dcom
Subject: Re: 2-line phone and modem problems
Message-ID: <1038@ulysses.UUCP>
Date: Sat, 10-Aug-85 14:11:23 EDT
Article-I.D.: ulysses.1038
Posted: Sat Aug 10 14:11:23 1985
Date-Received: Mon, 12-Aug-85 06:21:43 EDT
References: <427@ucdavis.UUCP> <1378@cbosgd.UUCP>
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 31

> In article <427@ucdavis.UUCP> ccohesh@ucdavis.UUCP (Hesh) writes:
> >my roomate recently bought a special 2-line phone; it
> >seems to be causing problems with my modem.  when this
> >phone is hooked up, i receive voluminous amounts of your
> >standard modem type garbage ("{i", "|}", etc.).
> 
> You didn't say what kind of modem or what kind of phone.
> However, a 2 line phone ought to be just a switch and a phone;
> if you don't have your phone picked up on the modem line it
> shouldn't do anything to your line.

For most phones, when they are on-hook, there's ring-detector cirucitry active.
Depending on the design of the phone -- I doubt that the problem is because
the new phone is 2-line.

> You might try making sure only the modem line pair gets to the
> modem.  I've installed modems through RJ-11 jacks and found that
> the second (supposedly unused) pair gets an incredible hum put
> onto it by the modem.  That is, I have a voice line and a data
> line and RJ14 jacks (e.g. regular modular jacks where the other
> line gets put onto the two extra pins.)  Some wall jacks have
> the voice line in the primary slot, some the modem line.  I plug
> the modem into a modem jack and suddenly there's a big hum on the
> voice line.  Never could figure out why.  I think this has happened
> with several different modems.  The fix is to get one of these plugs
> with 3 outputs - line 1, line 2, and both, and plug your modem into
> a "line 1" jack, which disconnects the line 2 leads.  Or do a little
> wiring to get the same effect.

Many modems provide A-A1 signalling on the other two lines, for use with
office key systems.