Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!pollux.usc.edu!papa
From: papa@pollux.usc.edu (Marco Papa)
Newsgroups: comp.sys.amiga
Subject: Modem Transfer Throughput (was Re: Dnet)
Keywords: Dnet, Telebit Trailblazer
Message-ID: <23299@usc.edu>
Date: 7 Mar 90 04:03:35 GMT
References: <25358@swrinde.nde.swri.edu> <1990Mar7.000117.6984@ncsuvx.ncsu.edu>
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In article <1990Mar7.000117.6984@ncsuvx.ncsu.edu> ml@ecerl3.UUCP () writes:
>A semi-related question about throughput:
>
>The modem does all sorts of data compression techniques to get its speed.
>Protocols like Zmodem also do compression.  

No. ZMODEM doesn't do any compression whatsoever.

>Will the compression done by Zmodem (or "compress" or "arc" or "squeeze"...)
>likely *decrease* the transmission rate when using data compression modes
>(MNP or PEP) on the modem?  (since applying a compression technique to data
>which is already well compressed often yields *worse* results).

If you "pre-compress" the program (whith compress, zoo, arc, squeeze) before
sending the file, you WILL LIKELY *decrease* the transmission rate IF you've
set up your modem to do compression itself. So best performance with modems
that support compression can be achieved either by:

a) transfer the original file "uncompressed", with your modem(s) compression
   turned ON.

b) compress the file at the origination site and turn OFF your modem(s) 
   compression.

Most modem manuals will suggest you to do a).

-- Marco
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