Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!lll-lcc!seismo!mimsy!aplcen!osiris!stsci!butler
From: butler@stsci.UUCP
Newsgroups: comp.dcom.modems
Subject: Re: REVIEW: Racal-Vadic 9600VP
Message-ID: <121@stsci.uucp>
Date: Wed, 25-Feb-87 20:54:50 EST
Article-I.D.: stsci.121
Posted: Wed Feb 25 20:54:50 1987
Date-Received: Sat, 28-Feb-87 06:10:08 EST
References: <1624@pyramid.UUCP>
Organization: Space Telescope Science Institute
Lines: 49

Last November I had to evaluate several high speed modems for use in some
networking applications.  I have always meant to do a full writeup and post
to the net, but have not had time.  My findings at the time were that the
RACAL-VADIC was more pleasant as an interactive use modem than the Telebit,
and was a bit cheaper.  A modem that was of interest but which arrived late
for me to do much testing and evaluation was the ADDCOM.  It looked to have
some of the features the VADIC lacked (speaker, line quality indicator).

As far as their use, we are using them to implement some phone links while
we wait for DDS lines from the Death Star company.  They don't show us the
throughput I wish they did (Still no comparison to a 9.6k DDS Line) but when
the packets get big, the modems push 'em through pretty good.  Throughput seems
to be more on the order of 7200 than 9600 (because of the resync'ing the
modem does I guess).  Telnet or "set host" are not the nicest things, but file
transfer isn't as bad as over 1200 baud modems by a long shot.  I have NEVER
seen a bad character come out of the modem.  I HAVE seen it hang up due to
line noise.

We had some real problems with our phone switch and these modems.  We ended
up getting direct lines from the local carrier for these modems.  Seems with
all the error correction and compression going on it takes a moment for the
modem to realize the phone has been hung up.  Our phone switch generates a
"Busy" signal when the remote party hangs up.  The modem kept trying to
recognize a carrier in the "busy" signal.  I'm not sure whether to blame the
modem or the phone switch.  The Telebit had a similar problem with the phone
switch.

There has been some difficulty getting trans-continental phone calls to connect
at something above 1200 baud.  It seems to depend on solar activity, lunar
position and Nancy Reagan's mood.


Perhaps I'll post more later if there is further interest on this subject.
Alternatively, interested parties should feel free to contact me at one of
the addresses below.


Lee A. Butler
Space Telescope Science Institute   3700 San Martin Dr.   Baltimore MD 21218
Arpanet: butler@stsci.arpa  |  butler@brl.arpa
 Usenet: seismo!stsci.arpa!butler | {noao,astrovax,cfa,charm,nrao1}!stsci!butler
   SPAN: scivax::butler (6405::butler)
  Phone: (301) 338-4531
-- 
Lee A. Butler
Space Telescope Science Institute   3700 San Martin Dr.   Baltimore MD 21218
Arpanet: butler@stsci.arpa  |  butler@brl.arpa
 Usenet: seismo!stsci.arpa!butler | {noao,astrovax,cfa,charm,nrao1}!stsci!butler
  Phone: (301) 338-4531