Path: utzoo!utgpu!watserv1!maytag!xenitec!zswamp!root
From: root@zswamp.fidonet.org (Geoffrey Welsh)
Newsgroups: comp.dcom.modems
Subject: MNP4
Message-ID: <3779.273A4638@zswamp.fidonet.org>
Date: Thu, 08 Nov 90 14:30:26 EDT
Organization: Izot's Swamp BBS - Kitchener, Ontario

Gihan Dias (dias@iris.ucdavis.edu ) wrote:

 >I've been following the discussion on MNP, etc. and have a 
 >question
 >about MNP4's operation. I know it packetizes data into 
 >"HLDC-like"
 >frames, and uses an ARQ protocol. What I'd like to know are:

 >  1. What is the maximum frame size?

 >  2. Does it do windowing or just stop-and-wait and, if so, 
 >what is the max window size?

   I can't answer that directly, but I think that I can correct some impressions 
that you have (and may Toby correct my every error! <grin>)

   I do not think that MNP4 in any way regulates the window size. MNP4 is like 
an 'option' on the base MNP protocols, exactly *one* of which is used as the 
foundation for any MNP connection. MNP1 through 3, as I understand them, are no 
windowing, windowing, and windowing with start/stop bit stripping respectively. 
MNP4 adds to *any* of these the ability to adjust the packet size dynamically.

 >The bottom line is: On an international link which may be 
 >subject to
 >satellite delays, is it better to use MNP4, or turn it off 
 >and use a
 >software protocol like windowed kermit?

   I have read that throughput may be improved on error-prone links by disabling 
MNP4, but I have not conducted enough experimentation in this area to provide 
any observations of my own.

 >Would V.42 be better than MNP4 in this regard?

   Again, I can only guess that LAP-M (remember, V.42 *includes* MNP4 in Annex 
A!) would provide better throughput because it was designed sufficiently later 
than MNP such that MNP's shortcomings would have been taken into account. 
Again, Toby would be better qualified to provide a direct answer.
 

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