Path: utzoo!attcan!uunet!wuarchive!bcm!dimacs.rutgers.edu!rutgers!news-server.csri.toronto.edu!utgpu!cunews!bnrgate!bigsur!bcars53!mussar From: mussar@bcars53.uucp (G. Mussar) Newsgroups: comp.dcom.modems Subject: Re: INFO-MODEMS Digest V90 #286 Message-ID: <1990Nov5.172154.9486@bigsur.uucp> Date: 5 Nov 90 17:21:54 GMT References: <3182.27310BB8@zswamp.fidonet.org> Sender: news@bigsur.uucp Organization: Bell-Northern Research, Ottawa, Canada Lines: 38 In article kim@Software.Mitel.com (Kim Letkeman) writes: >w3In article kim@Software.Mitel.com (Kim Letkeman) writes: > >| In article <3182.27310BB8@zswamp.fidonet.org> root@zswamp.fidonet.org (Geoffrey Welsh) 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 > ^^^ > sorry ... 234cps. > >| to maintain 274cps over a long .ZIP file. This kind of blows your >| argument up a bit. Zmodem sends 10 bit async chars (1 start, 8 data and 1 stop). With non-MNP, these chars are sent between the modems as 10 bits each as well. This means that maximum performance is limited to 2400/10 = 240 chars/second (minus any Zmodem overhead). I think 234 is about right. When you use MNP class 3 and about, the data sent between the modems is synchronous (HDLC based). Each byte requires 8 bits rather than 10 (minus HDLC framing/CRC/control). This means taht class 3 performance will top out just under 2400/8 = 300 chars/second. Again, 274 is about right. The performance gain you've seen is not due to class 5 compression but due to class 3 sync transfer between the modems. What the original poster was saying was that by turning off LZW compression you should not see any degradation of your 274 cps (and might even see a slight increase). Give it a try. -- ------------------------------------------------------------------------------- Gary Mussar |Bitnet: mussar@bnr.ca | Phone: (613) 763-4937 BNR Ltd. | UUCP: ..uunet!bnrgate!bcars53!mussar | FAX: (613) 763-2626