From: medin@cincsac.arc.nasa.gov (Milo S. Medin)
Subject: Re: USR modems..
Organization: NASA Science Internet Project Office
Date: Sun, 10 Jan 1993 01:34:04 GMT

In article <C0LwJK.C61@news.rn.com>, larry@news.rn.com (Larry Snyder) writes:
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|> I think both modems are excellent.  Neither modems gets my vote for fax.
|> USR is great for free firmware upgrades for the life of the modem even
|> if enhancements are included.  Telebit offers good support for bug fixes
|> and system integration.  The USR is excellent for real time v.32bis latency
|> and of course HST support while the WB works just dandy with PEP/TurboPEP
|> and supports up to 115200 baud.
|> 
...
|> -- 
|> Larry Snyder                                    internet: larry@gator.use.co
m
|> keeper of the Gator                                   uucp: uunet!gator!larr
y

Well, we have been having a lot of problems with rack mounted sets of USR 
V.32bis (not DS) modems, hung off off both PBX analog ports and a T1 
channelbank.  Things work fine unless you are using V.32 or V.32bis.  
Then you either don't sync up, or frequently get disconnected into a session.
I should also say these modems work fine when connected to straight 
centrex connected via copper to a CO about 2 miles away.  This is even after
installation of attentuation on the lines, and a lot of level adjusting.
This has caused us nothing but grief.  Our USR sales guy told us that
"you really shouldn't connect modems directly to a PBX".  The USR tech. 
support people have been trying hard, but have not managed to solve or even
identify the problem. 

The Worldblazers work much better over exactly the same configuration 
lines.  We replaced a rack of USR's on the west coast with a rack of 
WB's, and life is much better.  This is NOT using PEP, but with V.32bis.
They simply work where the USR's aren't stable.

We're now looking to see about replacing the bank on the east coast with
WB's too.  Any Government organization interested in trading us a rack
of WB's for USR's???  Oh, the PBX in question here is a Northern Telecom
SL/100.  The NTI folks have been unable to figure out why the USR's have so
many problem off the directly attached ports when they work fine on PacBell
centrex lines, even with padding and level adjustment.

We thought we would be better off cabling things this way because we minimized 
the analog loops as much as possible (none on the east coast site at all, since
it's hung directly off a channelbank), but the USR's don't seem to like this
configuration at all.  Also, since we are using an FTS 2000 800 number service, 
and both sites have FTS 2000 calls routed over dedicated T1's from AT&T, it's
very difficult just to wire the modems up off of LEC CO's.  Both racks are
wired to Annex III terminal servers on the DTE side.

So, if you are planning on installing modems directly off PBX's or T1
channelbanks, beware, and make sure you test out whatever modem configuration
you are planning first.  We thought that standards would make this simple,
and it looks like we were proved wrong.

						Thanks,
						   Milo

PS usual disclaimers apply of course
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