Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!mcsun!ukc!axion!galadriel!pcf
From: pcf@galadriel.bt.co.uk (Pete French)
Newsgroups: comp.unix.wizards
Subject: Re: FCC doing it again...
Message-ID: <532@galadriel.bt.co.uk>
Date: 6 Dec 89 09:45:23 GMT
References: <1989Dec2.070734.3853@stb.uu.net>
Organization: RT6115, BTRL, Martlesham Heath, England
Lines: 32

From article <1989Dec2.070734.3853@stb.uu.net>, by michael@stb.uu.net (Michael Gersten):
> This may sound like a dumb question, but...
> 
> How can the phone company multiplex any conversation, voice or modem?
> The phone company does not know ahead of time when there will be
> silence on the line, both are sampled at the same frequency, so there
> is the same total amount of data to be sent off, so they should be
> identical for multiplexing purposes, right?
> 
> Or am I missing something very important here?

No, your not missing anything, they are all sampled the same and multiplexed
the same. There is no difference between the calls - they are just audio
signals as far as the exchange is concerned - that the the whole point of a
modem, to make turn a binary signal into a form which is identical to a voice
so that it can be carried over the PSTN.

I find it extremely difficult to think of any reasons for a telephone company
to not want to carry modem calls - BT actually started a service (PRESTEL)
to encourgae people to use modems to increase the revenue from local calls.
I think the French did something similar and handed out freee terminals !
The only modem calls that I have ever heard objected to were those using
Bell frequencies rather than CCITT, aparrently because they interfered with
signals used between exchanges.


-Pete French.
-- 
       -Pete French.               | "The rhythm's gone,
  British Telecom Research Labs.   |  The radio's dead.
 Martlesham Heath, East Anglia.    |  And the damage done,
All my own thoughts (of course)    |  Inside my head."