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From: jwb@cit5.cit.oz (Jim Breen)
Newsgroups: comp.dcom.telecom
Subject: Re: TCP/IP over ISDN Basic Rate
Message-ID: <telecom-v09i0508m03@vector.dallas.tx.us>
Date: 14 Nov 89 00:00:10 GMT
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X-TELECOM-Digest: volume 9, issue 508, message 3 of 7

> Continuing Torsten Dahlkvist and Jim Breen's
> little discussion about byte/bit transmission over ISDN.

> We're looking at different levels of the system. The ISDN frame
> consists of a frame recognition pattern, D-channel bits and B-channel
> BYTES.  [...]

This is correct for the S-bus interface, and for the T interface for
Basic Rate. Primary Rate is different.

>   [...]                           Since maintaining the byte-wise sync
> is absolutely crucial for telephony, [....]

Now that Torsten has amplified his original statment, I agree with
*most* of what he says. The exigencies of telephony will result in a
de-facto byte synch, which can potentially be exploited by
manufacturers. We need to watch out, though. If one device always
expects an HDLC Frame octet to turn up in "synch", but the sender
offsets it a bit (as it is allowed to do), we will have no
communication.


> >> Aren't there ANY byte-oriented protocols [...]

> >Sure, there are several: HDLC, LAPB, etc. etc. [..]

> You seem set on insisting that we stick to the same old methods we've
> used all along. I suppose that's safer from many points of view. As a
> (former) designer of the systems involved, however, I feel it's a
> shame that we can't let them come to full advantage by making use of
> all the inheritent possibilities.

> On the other hand, maybe the net gain from eliminating the HDLC frame
> info from the data stream isn't big enough to justify the work of
> specifying a new standard. Some kind of flow control, packeting and
> such would still be needed, so it might turn out not worth it in the
> end.

I quite agree. There is a potential gain if you could insist on
all devices alligning their frames with the ISDN frames, but 8
bits is not much overhead. Also, you need some way to mark start
and end of frame.

        _______           Jim Breen (jwb@cit5.cit.oz) Department of Robotics &
       /o\----\\     \O      Digital Technology. Chisholm Inst. of Technology
      /RDT\   /|\   \/|   -:O____/         PO Box 197 Caulfield East 3145
     O-----O        _/_\    /\ /\          (p) 03-573 2552 (fax) 572 1298