Path: utzoo!utgpu!watserv1!maytag!xenitec!zswamp!root
From: root@zswamp.uucp (Geoffrey Welsh)
Newsgroups: comp.dcom.modems
Subject: 38.4 kbps for $169!?
Message-ID: <27.2828016C@zswamp.uucp>
Date: Wed, 08 May 91 03:04:05 EST
Organization: Izot's Swamp BBS (FidoNet), Kitchener, Ontario

In a letter to All, Chris Swanson (swansonc@grendel2.acc.stolaf.edu ) wrote:

re: CompuCom SpeedModem

 >Has anybody worked with this modem?  While it is proprietary,
 >it would be a cheap way to get some descent SLIP/PPP performance (if
 >the throughput is as good as they say).

   The device is either half duplex or asymmetrical, and the benchmarks given 
are unidirectional (as well as cooked, as are all good advertising 
'facts'[*]); you'll probably get much better SL/IP or PPP performance with a 
full duplex modem *like V.32 or V.32bis).

[*] NOTE: Every manufacturer who puts data compression on their modems and 
allows the host computer to talk to the modem at an RS-232 async speed higher 
than the physical link rate loves to claim that the modem is 'capable' of the 
highest link rate.  That means precisely diddley/sqat in terms of what the 
modem will do for you!  Today for the fun of it I fed a specially prepared 
file through a 2400 bps V.42bis-equipped modem and achieved a throughput in 
the vicinity of 950 CPS... on a 2400!  Of course, the onlookers were 
disappointed when they saw that the file was completely useless, but the 
point is that such an experiement could well be used to justify the claim 
that 4:1 data compression is possible... that doesn't avoid the fact that you 
shouldn't count on more than 2:1 compression on text and that compressed data 
will receive about 25% boost from asynchronous framing (the stripping of 
start & stop bits), and that's about it.  When transferring compressed files 
using the SpeedModem, you should count on throughputs in the vicinity of 1160 
CPS (just like V.32, and 2/3rds of V.32bis)... *not* 3840!

 

--  
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