Path: utzoo!attcan!uunet!lotus!esegue!johnl
From: johnl@esegue.segue.boston.ma.us (John R. Levine)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Modems and Telephone Lines
Message-ID: <1989Nov20.200531.8246@esegue.segue.boston.ma.us>
Date: 20 Nov 89 20:05:31 GMT
References: <13410@eerie.acsu.Buffalo.EDU> <1989Nov20.135228.2503@ug.cs.dal.ca>
Reply-To: johnl@esegue.segue.boston.ma.us (John R. Levine)
Followup-To: comp.dcom.modems
Distribution: na
Organization: Segue Software, Cambridge MA
Lines: 16

In article <1989Nov20.135228.2503@ug.cs.dal.ca> morrison@ug.cs.dal.ca.UUCP (Brad Morrison) writes:
>For most phone lines there are four wires.  They are really two pairs of
>wires.  Each pair is for a separate phone line.  ...

Sometimes yes, sometimes no.  There are about ten different ways that a
four-wire modular jack can be hooked up.  The usual scheme with one phone
line is RJ11.  Two lines is RJ14.  The original question was about a key
system where there is an in-use light on the phone for each line; that takes
an RJ12 or RJ13 where the third and fourth wires are for the in-use relay, in
which case the center two wires (red and green) are for the phone and next
two (yellow and black) are the A and A1 wires which the modem needs to short
together while it's using the phone.
-- 
John R. Levine, Segue Software, POB 349, Cambridge MA 02238, +1 617 864 9650
johnl@esegue.segue.boston.ma.us, {ima|lotus|spdcc}!esegue!johnl
"Now, we are all jelly doughnuts."