Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!uunet!hayes!tnixon
From: tnixon@hayes.uucp
Newsgroups: comp.dcom.modems
Subject: Re: HST/V.32bis Performance
Message-ID: <3811.27ca371e@hayes.uucp>
Date: 26 Feb 91 10:23:26 GMT
References: <139@ns.UUCP>
Organization: Hayes Microcomputer Products, Norcross, GA
Lines: 28

In article <139@ns.UUCP>, bob@ns.UUCP (Bob Mathias) writes: 

> I have noticed that with my new USR DS modem, that HST mode seems to 
> outperform v.32bis when doing file transfers using YMODEM-G on a PC-based
> BBS.  I run both with v.42 and v.42bis is disabled.  The speed difference
> is about 30cps.     
> 
> I'm not really concerned about this speed differential since it is not that
> great and I'd rather use a non-proprietary protocol.  I am just curious as
> to why this might be.

There should be NO difference, if you're using MNP4 in both HST and 
V.32bis mode.  Normally, the reason people see a difference in 
performance is because the maxmimum frame size in MNP4 is 256 bytes, 
and the _default_ maximum frame size in V.42 LAPM is 128 bytes.  The 
LAPM default can be negotiated higher, but the HST doesn't because
of memory limitations.  The resulting smaller frame size increases 
protocol overhead and causes throughput to be about 2% less.  I 
can't think of any other reason why asymmetrical modulation would 
provide higher throughput than V.32bis, except, as you note, perhaps 
some difference in USR's implementation that unnecessarily cripples 
their V.32bis (although fortunately not by much).

-- 
Toby Nixon, Principal Engineer    | Voice   +1-404-840-9200  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