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From: csowden@compulink.co.uk (Chris Sowden)
Newsgroups: comp.dcom.telecom
Subject: Re: Data Lines vs. Voice Lines
Message-ID: <12633@accuvax.nwu.edu>
Date: 25 Sep 90 20:39:00 GMT
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X-Telecom-Digest: Volume 10, Issue 681, Message 7 of 11


There is a CCITT recommendation describing Digital Circuit
Multiplication Equipment (DCME) which improves the efficiency of
international trunks.

DCME works by encoding the speech data from 64kbit/s down to a lower
rate such as 32kbit/s (ADPCM) and by only connecting the speech
channel to a trunk when it is carrying a burst of speech (Digital
Speech Interpolation).  DCME, while not quite fitting the packet
model, does allow a number of 64kbit/s speech channels to be carried
on a smaller number of transmission channels.

Voice band data, OTOH, is not suitable for compression by DSI.  Also,
ADPCM can cause problems with high speed voice band data.  Digital
data (ISDN) requires a whole channel to itself.

DCME can only be cost effective where the circuit costs are high (long
trunks).  If DCME is used, data calls will require more bandwidth on
these trunks than voice calls.  Therefore, data calls will cost the
operator more to carry.


Chris Sowden