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From: root@zswamp.uucp (Geoffrey Welsh)
Newsgroups: comp.dcom.modems
Subject: Help with v.42bis standard?  I'm confused.
Message-ID: <148.28486D87@zswamp.uucp>
Date: 2 Jun 91 00:29:11 GMT
Article-I.D.: zswamp.148.28486D87
Organization: Izot's Swamp BBS (FidoNet), Kitchener, Ontario
Lines: 66

Bryan_Jones_Woodworth@cup.portal.com wrote:

 >I am planning on buying a modem supporting mnp5 and v.42bis, 
 >which allow it to transfer at speeds up to 9600 bps.

   I presume you mean a 2400 bps modem with V.42bis, right?

 >Will this really go at 9600bps?

   No.  It's a 2400 bps modem, and 2400 bps is exactly how fast its *physical* 
carrier will go.  The advertisement "up to 9600 bps" is based on data 
compression, which is useless in the vast majority of situations.

   Still, in an effort to find out exactly how accurate the ads are, I've 
often sumbitted new V.42bis modems to the test of feeding it a megabyte of 
nulls and determining how fast it can move them using YMODEM-G... even with 
ideally compressible data, it never approaches 960 CPS.

 >Will it connect at 9600 with USR HST modems?

   Fact #1 (and don't you ever forget it): There is only one modem on Earth 
that will connect at 9600 (or 14400) bps with a USRobotics Courier HST... and 
that's the USRobotics Courier HST.  This is unlikely to change.

   USR's Courier HST Dual Standard (sometimes referred to as just "Dual 
Standard") will also speak to V.32 modems at 9600 (and, with USR's latest 
models, with V.32bis modems at 14400 bps).

   No, V.42 doesn't have anything to do with V.32; V.42 is a protocol to 
packetize data and correct errors, while V.32 describes how bits are to be 
turned into signals that can be transmitted over the phone line.  They perform 
different jobs, so don't even as if they're compatible (it would be like 
asking if a Porsche was compatible with orange paint).

 >I've seen some v.42bis modems that support 9600bps (like the 
 >one I want),

   They're really 2400 bps modems, but you talk to them at 9600 bps so that 
the extra throughput (typically 280 CPS for compressed files, much higher on 
text) can be realized.  They don't actually move real data at 9600 bps.

 >others that support 19.2K (v.32), 19.2k (v.32/v.42), 38.4k 
 >(v.32/v.42bis)..

   V.32 means 9600 bps full duplex.  Again, the modem will speak to the 
computer at a speed of 19,200 bps (or, for optimistic manufacturers, 38,400 
bps), but the modem itself is 9600 bps and typical throughput for compressed 
files is around 1160 CPS.  V.32bis and the 14.4 kbps HST are 14,400 bps 
modems, and they will move compressed data around 1750 CPS.

 >I am worried that I won't get fast speed with modems..

   Your first worry should be that manufacturers are taking advantage of the 
general ignorance of the public to make their products sound faster than they 
really are.

   Lean back and read this conference for a while, and you'll get a better 
feel for what all the fancy words mean and what a particular brand of modem 
can do for you.
 

--  
Geoffrey Welsh - Operator, Izot's Swamp BBS (FidoNet 1:221/171)
root@zswamp.uucp or ..uunet!watmath!xenitec!zswamp!root
602-66 Mooregate Crescent, Kitchener, ON, N2M 5E6 Canada (519)741-9553
"He who claims to know everything can't possibly know much" -me