Path: utzoo!mnetor!uunet!husc6!ukma!nrl-cmf!ames!pasteur!agate!eris!chapman
From: chapman@eris (Brent Chapman)
Newsgroups: comp.dcom.modems
Subject: Re: MNP make for a faster modem?
Message-ID: <6701@agate.BERKELEY.EDU>
Date: 25 Jan 88 06:16:27 GMT
References: <3027@killer.UUCP> <6678@agate.BERKELEY.EDU>
Sender: usenet@agate.BERKELEY.EDU
Reply-To: chapman@eris.UUCP (Brent Chapman)
Organization: UNIXversity of California at Berkeley
Lines: 31
Keywords: MNP

In article <6678@agate.BERKELEY.EDU>, I write:
#In article <3027@killer.UUCP> tony@killer.UUCP (Tony Holden) writes:

#>I've seen ads claiming that with the various MNP levels that the throughput
#>on a 2400 baud modem is that of 9600 baud.  
#>
#>Is it hype or is it real?

#It's hype.  MNP is an error detection and correction protocol.  A modem running
#at 2400 baud with MNP will probably actually have slightly (_very_ slightly)
#lower throughput than without MNP, because of the extra bits needed for the
#protocol.  I happen to think it's worth it, though, because of the error
#correction.

I've been informed that higher levels of MNP include compression as well as
error detection and correction.  Even so, I find a 4 to 1 compression ratio
hard to believe under any "real" conditions, especially in interactive use.
The "compress" program, which is pretty good according to the people I know
who know about such things (I don't), rarely manages a 4:1 ratio, and then
only on large, fairly repetitious files; I doubt the ability of any modem
to do much better, because it can't use _too_ large a "block size" for
compression because of response time considerations.  [I'd be happy to
be shown to be wrong, however...]


-Brent
--
Brent Chapman					Capital Market Technology, Inc.
Senior Programmer/Analyst			1995 University Ave., Suite 390
{lll-tis,ucbvax!cogsci}!capmkt!brent		Berkeley, CA  94704
capmkt!brent@{lll-tis.arpa,cogsci.berkeley.edu} Phone: 415/540-6400