From: Rob Chandhok <Ravinder.Chandhok@CS.CMU.EDU>
To: Harry Bovik <bovik+@K.GP.CS.CMU.EDU>
Subject: modem info
Date: Tue, 05 Feb 91 12:39:32 EST
Message-ID: <9310.665775572@GNOME.CS.CMU.EDU>
Sender: Ravinder.Chandhok@GNOME.CS.CMU.EDU


As promised, here's what I have found out so far about modems, CMU/CS/RI
connections, and the like.  Most of my information comes through Paul Parker
of Facilities, and from some other reading.  Thanks to Paul for all his help!

1) Regarding the benfit or speedup of the newly bought 2400 baud MNP5
modems:  MNP5 is the Microcom implementation of lempel-ziv compression.
It's characteristics (table size, etc) limit it to at maximum a 2.5 times
speedup.  Anyone familiar with the algorothm will realize that the actual
speed depends on what you are trying to compress.  Text files do real well.
If you use an 2400 baud MNP5 modem, you can connect your terminal to it at
9600 baud, since you will get bursts of characters at that speed.  
Please realize that the compression produces bursty output.  People using
the MNP5 modems report that it makes a difference, and they are happy with
the performance.

You should be able to get a 2400 MNP5 modem in the $200-300 range.  But
beware, different brands of modems perform differently under poor line
conditions.  There is general agreement that the Hayes modems perform well.
One article also says that US Robotics modems look good also.  I don't know.
Other brands are also good, I haven't found enough reviews to make a good
summary here.

The "V.42bis" is also a compression standard, which claims to provide up to
4 times the compression (although I suspect the actual performace is close
to MNP5).  The big difference between V.42bis and MNP5 is that MNP5 tries to
compress everything, and binary data usually expands.  V.42bis can detect
random data and choose not to compress it.  V.42 is also a public domain
standard.  A lot of modems will do both MNP5 and V.42bis.

2) There don't seem to be any higher speedlines on campus available for
general use.  Some people in the department have private 9600 baud modems,
but they are still a bit pricey.

3) No one seems to understand why you might have a 2400 baud modem that
claims to be a 9600 baud fax modem.

4) CS/RI has no immediate plans to upgrade to 9600 baud modems, but that
doesn't mean it won't happen.  A lot depends on the CS/RI budget, and how
much the new modems drop in price.  A 9600 modem is currently in the
$700-1000 range.

cc: Bovik