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Path: utzoo!mnetor!seismo!epiwrl!parker
From: parker@epiwrl.UUCP (Alan Parker)
Newsgroups: comp.sys.misc
Subject: Re: Re: Pending FCC ruling threat to modem users
Message-ID: <886@epiwrl.UUCP>
Date: Fri, 19-Dec-86 22:37:16 EST
Article-I.D.: epiwrl.886
Posted: Fri Dec 19 22:37:16 1986
Date-Received: Sat, 20-Dec-86 04:07:14 EST
References: <1575@brl-adm.ARPA> <126@dvm.UUCP> <4334@mit-eddie.MIT.EDU>
Reply-To: parker@epiwrl.UUCP (Alan Parker)
Organization: Entropic Processing, Inc., Washington, DC
Lines: 24

In article <4334@mit-eddie.MIT.EDU> jbs@eddie.MIT.EDU (Jeff Siegal writes:
>When you call your friendly BBS (or your grandmother), the phone
>company's equipment does not simply throw a few switches and connect
>you.  Your call gets routed over inter-office trunks, which are shared
>between many calls.  One of the ways they make finite trunk capacity
>go further is by multiplexing calls.  For example, in the time between
>the words "hello" and "Granny", someone else is using the channel
>you're not using (because you're being silent).  For normal
>conversation, this "silent time" is a substantial percentage of the
>call time.  With modem calls, there is no idle time.  Even when no
>data is being transfered (and data is often transfered continuously
>for long periods of time), the channel is being used by the modems
>which need to exchange carrier signals.

Bull.   Very few (if any) trunks work this way.   For the most part
Digital trunks are TDM mutiplex using either 64K bps per call
(for regular PCM) or 32K bps (for APCM).   Older analog carrier trunks
(of which there are still plenty of out there) assign a piece of the
frequency domain to each call.   These do not have the smarts to move
calls around during silence periods.

A scheme like you describe might be used by a carrier on long haul
(particularly satellite) circuits.   I think the original SBS system
worked this way (and it didn't work well).