Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!uunet!ccicpg!uis-oc!ns!bob
From: bob@ns.UUCP (Bob Mathias)
Newsgroups: comp.dcom.modems
Subject: Re: HST/V.32bis Performance
Message-ID: <141@ns.UUCP>
Date: 4 Mar 91 18:35:44 GMT
References: <139@ns.UUCP> <3811.27ca371e@hayes.uucp>
Reply-To: bob@ns.UUCP (Bob Mathias)
Organization: Unisys Corporation; Irvine, California
Lines: 29

In article <3811.27ca371e@hayes.uucp> tnixon@hayes.uucp writes:
>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).

I was using V.42 LAPM during my performance tests for both protocols 
(V32.bis and HST).  I wasn't aware of the difference in frame size 
between V.42 LAPM & MNP4 so I decided to do the tests using MNP4 instead.
This improved my performance for both protocols.  I now get 1732 cps
for HST and 1723 for V32.bis (less than a 1/2 % difference).   

MNP4 improved by HST performance by about 17 cps and my V32.bis by about
42 cps.  Since I'm seeing such a difference, is there any why I shouldn't
disable LAPM and use MNP4.  What are the benefits of LAPM over MNP4?


-- 
Bob Mathias                          uucp: ...!uunet!ccicpg!uis-oc!ns.UUCP!bob
Unisys Corporation                   CServ: 70340,165 
A and V Series Systems Engineering   voice: (714) 727-0323  
Irvine, California