Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!elroy.jpl.nasa.gov!decwrl!uunet!hayes!tnixon
From: tnixon@hayes.uucp
Newsgroups: comp.dcom.modems
Subject: Re: V.42bis vs. MNP5
Message-ID: <3936.28274a04@hayes.uucp>
Date: 8 May 91 00:44:52 GMT
References: <1991May7.183758.14662@prism.poly.edu>
Organization: Hayes Microcomputer Products, Norcross, GA
Lines: 48

In article <1991May7.183758.14662@prism.poly.edu>,
drubin@prism.poly.edu (Dave Rubin) writes: 

> I am in the process of upgrading our dialup modems, most likely with some
> combination of 9600bps and 2400bps modems.  Our telephone switch cannot
> handle async speeds over 19.2kbps.  Therefore, the potential 38.4kbps
> throughput of V.32/V.42bis modems would probably be wasted.  Is there any
> other reason to go with V.42bis on our V.32 modems?

Certainly!  If you had no data compression at all, you'd only get 
about 1150cps max.  With MNP5 you could approach 1920cps on 
highly-compressable files, but are more likely to see in the 
neighborhood of 1500-1600 on "typical" text -- and MNP5 will have a 
negative impact (less than 1150 cps) on throughput while sending 
uncompressible data.  With V.42bis, you'll see the full 1920cps 
through much more of the time.  Even though the algorithm is capable 
of much more, it's not "wasted" because it does allow you to take 
advantage of all the bandwidth you actually have available.  Since 
many companies sell V.42bis modems for no more than they sell MNP5, 
you might as well get V.42bis.

> As for 2400bps, for standard dialup applications, is there much to gain by
> choosing V.42bis over MNP5?  We plan on setting the DTE rate at a constant
> 9600bps regardless of the actual speed of the connection.

Absolutely.  Again, MNP5 gets about 2-to-1 (480cps) on highly 
compressable data, but more like about 350-400 on "typical" data.  
V.42bis will typically do at least 50% better (600-700cps on 
"typical" data) and 900cps+ on well-compressible data.  I can 
definitely perceive the difference between V.42bis and MNP5 on the 
same data.

> Finally, does anyone have a recommendation for inexpensive (but reliable)
> V.32 and 2400bps modems, preferably rack-mountable, that can be set to a
> "manual" mode (where the modem plays dumb and allows our PBX to control it).

Since I work for a modem manufacturer, I'll let other folks make the 
recommendations.  :-)  However, I will point out that FEW of the 
V.32 multimode modems with V.42bis on the market today support 
MI/MIC operation (which is what you want); the Hayes Ultra 96 is oen 
that does.  Perhaps some users of other modems can check their spec 
sheets and see if they support MI/MIC.

-- 
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