Re: ISDN phone lines

From: Richard H. (rh86_at_no.spam)
Date: 03/26/05 

Date: Sat, 26 Mar 2005 08:08:44 -0700

Michael wrote:
> Do most of the ISDN phone "systems" have this ability?
> (I would think they ALL would have this endpoint bulit in?).

Yes, I'd expect so. There are a lot of possible scenarios, but if the
system is talking ISDN to the carrier and POTS to the phone sets, then yes.

> I wanted to detect ring with a normal POTS detector at 90vac---I would
> imagine they generate the same (or close).

Yes. On a POTS interface, they are expected to meet the standards, and
appear as a telco switch in terms of dial tone, ring patterns, voltage
levels, etc.

> My question was more about ISDN "systems" rather than just a single
> dedicated line and certainly they're going to be backwards compatible.

In effect, the question of whether it's ISDN upstream should be
irrelevant if the interface to you is POTS. Translating is the job of
the "system", and downstream devices should neither know nor care. In
practice, the upstream trunk could be any variety of analog line,
channelized T1/E1, ISDN PRI/BRI, or even VoIP.

FYI, many "phone systems" use digital phone sets, and the line between
the desk set and the PBX/key system is a proprietary vendor protocol,
not POTS. Your POTS ring detector won't work on these lines.

> This "D" channel ring stuff was scaring me.

You'd only care about that if you were monitoring the ISDN line, not the
POTS line. That's a whole different ball game, magnitudes more complex,
requiring you to monitor and decode a digital signal.

Cheers,
Richard

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