Path: utzoo!utgpu!news-server.csri.toronto.edu!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: <2650@hayes.uucp> Date: 6 Nov 90 13:14:34 GMT References: <3182.27310BB8@zswamp.fidonet.org> Organization: Hayes Microcomputer Products, Norcross, GA Lines: 30 In article , kim@Software.Mitel.com (Kim Letkeman) writes: > | 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!). > > Well, my own experience contradicts this. With my old SmartTeam > 2400bps modem I was very pleased that ZMODEM would tool along at an > average speed of 134cps or so. My new ATI with MNP5 was actually able > to maintain 274cps over a long .ZIP file. This kind of blows your > argument up a bit. I've heard that "compress" files don't go as well, > but my own experience is that "ZIP" files do ok. I certainly won't be > turning off compression for ZMODEM transfers. What you don't understand is that MNP4 (with MNP5 turned off!) can transfer 292 cps! That difference (from 292 down to 274 cps) is very likely caused by MNP5 _expanding_ your data. MNP3 and MNP4 (and LAPM) gain throughput by stripping the start and stop bit off each character; that by itself would increase the throughput of a 2400bps modem from 240cps (10 bit per character) to 300cps (8 bits per character), but you have to subtract out the protocol overhead leaving a capacity of 292cps for MNP4 or about 263cps for MNP3. -- Toby Nixon, Principal Engineer | Voice +1-404-449-8791 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet hayes!tnixon@uunet.uu.net