telecom@ucbvax.ARPA (03/24/85)
From: Jon Solomon (the Moderator) <Telecom-Request@BBNCCA>
TELECOM Digest Sat, 23 Mar 85 19:00:52 EST Volume 4 : Issue 172
Today's Topics:
Re: Microcom Networking Protocol
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Date: 19 Mar 1985 14:33-EST
Subject: Re: Microcom Networking Protocol
From: WTHOMPSON@BBNF.ARPA
To: Telecom-Request@BBNCCA.ARPA
Cc: WThompson@BBNF.ARPA
Some of the information you seek concerning MNP may be found in
the August 1984 issue of "Data Communications," in a discussion
on protocols. The MNP protocol is proprietary, and I'm not sure
how much exact detail is available, short of paying $2,500 for a
licensing agreement. I know there is a variable-length header,
and that the protocol can take up less than 8 kilobytes (this
info is in the article).
In answer to your second and third questions: when trying to
establish a connection over very noisy lines, you may be able to
establish the connection itself without being able to establish
the MNP portion of the connection. (MNP must be present and
active in both modems for it to work, however it is certainly
possible to dial in to non-MNP modems. The connection will
simply not have error correcting capabilities.)
Of course there is an overhead for all of this, and with MNP
implemented the modems and the protocol insist on flow control.
MNP ignores the switch settings concerning flow control and
implements its own, which consists (I think) of hardware flow
control from DCE to DTE, and of software flow control between
DCEs. (I may have that backward.) In tests I have run with
these units in reliable mode, overhead can range from minimal to
14%. I think the modems must clear their buffers before resuming
transmission, rather than waiting for a percentage of buffer to
become available, but that is strictly a guess.
Lastly, I believe the reference to "standard" refers to the
implementation of MNP or MNP modems by such groups as Telenet,
MCI Mail, Uninet, and others. I know that Telenet has
established special Microcom numbers in their public dial
facility. I guess that makes a standard....
WCT
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End of TELECOM Digest
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