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From: jst@wucs.UUCP (Jon Turner)
Newsgroups: net.dcom
Subject: Re: Packetized Voice
Message-ID: <967@wucs.UUCP>
Date: Mon, 27-May-85 11:51:54 EDT
Article-I.D.: wucs.967
Posted: Mon May 27 11:51:54 1985
Date-Received: Wed, 29-May-85 23:44:12 EDT
References: <438@wdl1.UUCP>
Reply-To: jst@wucs.UUCP (Jon Turner)
Organization: Washington U. in St. Louis, CS Dept.
Lines: 53
Summary: 

In article <438@wdl1.UUCP> jbn@wdl1.UUCP writes:
>
>       The TASI subchannel-assignment system used on transoceanic cables
>for decades avoids tying up the channel during silent periods, and achieves
>roughly similar bandwidth economy.  And most newer switching systems,
>especially PBXes, are digital circuit switches and handle both voice and data
>in a similar way.  You don't need packet switching to achieve these gains.
>
TASI can give you the same bandwidth gains as packet switching, but it's
purely a transmission system. As soon as you reach a switching system the
signals are separated back out to the full 64 Kbs. Consequently the
compression must be repeated for each hop. There are switching techniques
that can carry the compressed signals through switching offices. None
of course, have been implemented on a large scale.

It is also true that you can get integrated voice and data communication
in digitial telephone switches, but only if you're happy with a 64 Kbs
circuit switched channel. The burstiness of most data applications makes
this a less than ideal option (yes I know, it sure beats 1200 baud modems).
The kind of system I referred to in my earlier note can provide channels
in any size from 100 bits per second to over a megabit per second, and
can handle bursty signals, charging the user only for what is used, not
for the silent periods.

>       It's interesting to hear that Bell Labs tried to build a big packet
>network.  I would appreciate references, if available.  To date, all packet
>networks have been tiny by telephony standards, and no one has convincingly
>demonstrated that packet switching technology can be scaled up to networks
>with millions of subscribers.

I never said that Bell Labs tried to build a big packet network, only that
they have done (and still are doing) research trying to establish that it is
feasible. Not much has been published to date. You can find two papers in
the Proceedings of Globecom 83. One is authored by Len Wyatt and myself,
the other by Bill Hoberecht. There is a paper by John Kulzer and Warren
Montgomery in the Proceedings of the International Switching Symposium (84)
and there are two papers in the December 83 issue of the IEEE Journal on
Selected Areas in Communications, one by Warren Montgomery and the other
Y. C. Jenq. There are also several patents which issued recently. I don't
have the patent numbers here (I'm typing this from home), but will be happy
to post them if there is enough interest.

>Most of the X.25-based systems are circuit switches underneath.

Huh? The ones I'm familiar with certainly are not circuit switches underneath.
What do you mean by circuit switching?

-- 

Jon Turner 	Washington University in St. Louis 314-889-6193
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