Path: utzoo!utgpu!watserv1!maytag!xenitec!zswamp!root
From: root@zswamp.fidonet.org (Geoffrey Welsh)
Newsgroups: comp.dcom.modems
Subject: New Modems
Message-ID: <4888.274A0A55@zswamp.fidonet.org>
Date: Tue, 20 Nov 90 20:56:34 EDT
Organization: Izot's Swamp BBS - Kitchener, Ontario

Evan Champion (evanc@isishq.fidonet.org ) wrote:

 >I like the Dual Standard's 14.4KB, and with v.42bis (I think) that 
 >puts it around 30kb correct? Anyway, any help would be appreciated.

   Manufacturers like to quote *potential* data throughput using data 
compression. I don't buy it, since much of the marterial passed through these 
high-speed links is already compressed. V.42bis will not significantly improve 
the throughput of .ZIP or .Z (compress) files.

   I like to concentrate on the *raw* data throughput rate and include, where 
appropriate, the gains realized by synchronous framing (that's throwing away 
the start & stop bits). In the case of the HST 14.4 (or the Dual Standard), 
the raw data rate is 14400 bits/second; using MNP4, that gives theoretical 
maximum data transfer rates approaching 1800 CPS *without* compression 
(assuming a low-overhead streaming protocol). The number for 9600 bps HSTs and 
V.32 modems is approximately 1200 CPS. The number for Telebit TrailBlazers is 
somewhere around 1400 CPS, tapering off as line quality degrades.

   Heck, if all you're doing is sending spaces, any of these modems will 
transmit the data as fast as you can send it to the modem from the computer, 
but that's not a useful benchmark as you will rarely be sending only spaces!

   Geoff

DISCLAIMER: I have not played with V.42bis, and cannot comment on its 
effectiveness beyond doubting that it will contribute *much* to precompressed 
files. I *have* played with MNP5 (which, as Toby has pointed out, is a vastly 
different technique) and usually turn it OFF as soon as I can because I get 
better overall performance *without* it. 
 

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