Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!hayes!tnixon
From: tnixon@hayes.uucp (Toby Nixon)
Newsgroups: comp.dcom.modems
Subject: Re: INFO-MODEMS Digest V90 #286
Message-ID: <2567@hayes.uucp>
Date: 2 Nov 90 18:20:03 GMT
References: <3182.27310BB8@zswamp.fidonet.org>
Organization: Hayes Microcomputer Products, Norcross, GA
Lines: 23

In article <3182.27310BB8@zswamp.fidonet.org>,
root@zswamp.fidonet.org (Geoffrey Welsh) writes: 

>    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.

Actually, because of protocol overhead, the maximum benefit from 
MNP3 is about 9.8%; with MNP4 (and V.42 LAPM), you can acheive about
a 22% increase.  The maximum theoretical benefit, without protocol 
overhead, would be 25% (10/8), but you have to remember to subtract 
out for frame headers, FCS, flags, and average zero-bit insertion 
(average of 1 for every 63 bits).

>    MNP5 uses a type of LZW compression algorithm...

MNP5 uses adaptive Huffman coding.  V.42bis uses LZW.

-- 
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