Path: utzoo!utgpu!watserv1!maytag!xenitec!zswamp!root
From: root@zswamp.fidonet.org (Geoffrey Welsh)
Newsgroups: comp.dcom.modems
Subject: Re: INFO-MODEMS Digest V90 #286
Message-ID: <3182.27310BB8@zswamp.fidonet.org>
Date: Thu,  1 Nov 90 08:53:59 EDT
Organization: Izot's Swamp BBS - Kitchener, Ontario

 > From: TIMBUCK@VTVM1.CC.VT.EDU
 > Message-ID: <9011010804.AA05071@ucbvax.Berkeley.EDU>
 >
 > As I understand it, MNP compression is independent of whether or not the
 > files are already compressed.  However, the modem at the "other end" must
 > also use MNP for you to use it.  Additionally, only certain file transfer
 > protocols use MNP (e.g. YMODEM-g).
 
   I don't know where you got these ideas!
 
   Modems which support MNP internally get a 20% boost in performance by 
stripping start and stop bits from the data stream (MNP Service Class 3), but 
this is not considered data compression.
 
   MNP5 uses a type of LZW compression algorithm, but its 'on the fly' 
approach has some weaknesses, including the fact that MNP5 will *lose ground* 
on well-compressed files (i.e. a .ZIP file moves faster with MNP5 *dis*abled 
than with it enabled!).
 
   It's true that both ends of a connect must support MNP for it to be 
effective, but that's like saying that a 2400 bps modem only works at that 
speed when calling another modem with 2400 bps capabilities... it should be 
obvious.
 
   As for your claim that "only certain ... protocols use MNP", I am not sure 
what you mean. While some protocols (such as YMODEM-G, XMODEM-1K-G, UUCP-e, 
etc.) *depend* on an error-free data link, no protocols are specific to MNP 
and MNP3's (and MNP5's) performance boosts can be used to advantage by just 
about any protocol. In some rare cirucmstances, MNP's packetizing delays may 
degrade the performance of non-windowed protocols with small packets, but this 
is purely a coincidental side-effect.
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