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From: zweig@brutus.cs.uiuc.edu (Johnny Zweig)
Newsgroups: comp.dcom.telecom
Subject: Re: TCP/IP over ISDN Basic Rate
Message-ID: <telecom-v09i0516m04@vector.dallas.tx.us>
Date: 16 Nov 89 18:27:01 GMT
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X-TELECOM-Digest: volume 9, issue 516, message 4 of 11

A codec needs a byte-stream. If ISDN is going to be used with real
live 8-bit codecs, there will have to be a byte-stream protocol on the
wire.  The frames already contain D-channel data as well as
off-hook/on-hook bits (or at least that is the Party Line), so no need
to do ugly nonsense like robbing the 8th bit.

I can whip up a SLIP at 64000bps that will make me happy if I have a
line that takes 8000 bytes every second and hands them to whoever I
called.  Routing and other considerations are research-problems and
belong in comp.protocols.tcp-ip.  I just want as many bytes/second as
I can squeeze out of the wire.  SLIP is a framing-protocol, so forget
HDLC. I promise to be the only one using the bits.

I just don't get this business of taking a byte-stream protocol and
layering a bit-stream protocol on it (lowering the bandwidth available
to payload), and then putting a byte-stream on that (using, say,
bit-stuffing and further lowering available horsepower).  Could
someone please explain? It seems dumb.

Now, if I envision having several interfaces contending for the 64kps,
I need a medium-access protocol such as HDLC. Fine. Let me call
someone who speaks HDLC if I want to use HDLC -- otherwise, let me use
all the bits and call someone who expects that.

HDLC is a bit-oriented protocol (see Tanenbaum, "Computer Networks",
p. 254).  It seems inappropriate, wasteful and silly to use it on a
byte-oriented physical medium (which ISDN has to be to support digital
telephony).

I just don't get it.

-Johnny Bits