Path: utzoo!telecom-request
Date: 9 May 91 07:09:07 GMT
From: John Nagle <decwrl!well.sf.ca.us!well!nagle@uunet.uu.net>
Newsgroups: comp.dcom.telecom
Subject: Re: Help Needed Understanding ISDN
Message-ID: <telecom11.349.9@eecs.nwu.edu>
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csense!bote@uunet.uu.net (John Boteler) writes:

> Unless the power fails at your location. Then, no more ISDN.

> OOPS!

     No, ISDN sets can be powered from the phone line.  The power
situation is ingenious.  Normally, you can draw (I think) 400ma
off-hook from an ISDN line.  This should be enough for a reasonable
phone, and maybe a digital answering machine as well.  If the CO has a
power problem (maybe when commercial power is out) the DC polarity of
the line is reversed, and you can then draw only some lesser amount of
power.  Maybe your dial light will go out.  But the phone should still
work.

     Now, which ISDN phones properly comply with the spec?


John Nagle