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From: ralphw@ius2.cs.cmu.edu (Ralph Hyre)
Newsgroups: net.dcom
Subject: Re: Want information on Zipper modem
Message-ID: <309@ius2.cs.cmu.edu>
Date: Fri, 14-Mar-86 12:53:02 EST
Article-I.D.: ius2.309
Posted: Fri Mar 14 12:53:02 1986
Date-Received: Sun, 16-Mar-86 09:44:07 EST
References: <12019@ucbvax.BERKELEY.EDU> <12900002@svo.UUCP>
Organization: Carnegie-Mellon University, CS/RI
Lines: 33

In article <12900002@svo.UUCP> corey@svo.UUCP writes:
>
>	AX/2400c	Same as regular AX/2400 but does data compression
>			between the serial port and the phone line so that
>			the phone line only sees 2400 baud but the throughput
>			is 4800 baud.
This seems reasonable.
>
>	AX/9612		Same as regular AX/2400 but does data transfers at 
>			9600 baud.
>
>	AX/9624c	Same as AX/9612 but does data compression
>			between the serial port and the phone line so that
>			the phone line only sees 9600 baud but the throughput
>			is 19.2K baud.

These don't.  It seems that the initial data compression (modem <-> modem)
would make it difficult to achieve any further reduction through data
compression techniques, since the already-compressed data would have no
regularity that can be exploited.  As Shannon might say:

    +++	
   +   ++			++++++++
  +      +			+      +

uncompressed data		compressed data
distribution			distribution (ideal)
-- 
					- Ralph W. Hyre, Jr.

Internet: ralphw@c.cs.cmu.edu (cmu-cs-c.arpa)	Usenet: ralphw@mit-eddie.uucp
Fido: Ralph Hyre at Net 129, Node 0 (Pitt-Bull) Phone: (412)CMU-BUGS