Date: Thu, 19 Nov 92 16:17:31 GMT
From: lars@spectrum.CMC.COM (Lars Poulsen)
Newsgroups: comp.dcom.telecom
Subject: Re: Advice Needed on Wide Area Networking
Organization: CMC Network Systems (Rockwell DCD), Santa Barbara, CA, USA
X-Submissions-To: telecom@eecs.nwu.edu
X-Administrivia-To: telecom-request@eecs.nwu.edu
X-Telecom-Digest: Volume 12, Issue 861, Message 7 of 9

In article <telecom12.858.9@eecs.nwu.edu> jeff@digtype.airage.com
writes:

[Some questions about how to connect two offices five miles apart with
TCP/IP (X terminals) and Appletalk.]

> We could eventually end up with six or so Xterminals and ten Macs.
> A 56kb line is the same installation cost as a T1, and the monthly
> difference is only $250/mo ($250/mo for a 56kb line, $500/mo for a T1).

> What kind of demands does X place on the network?
> Will a 56kb >line be sufficent, or should we jump to the T1?

If you have enough money in the budget to easily afford the bandwidth,
go for the T1. While your average traffic will probably fit in the
56Kbps line, there will be times when you are waiting for the line.

The performance needs of X terminals depend enormously on the
applications. Some applications transfer enormous amounts of data to
support what looks like modest displays. I recently saw an X dialog
editor, which transferred about 250 KB before turning the window on.
It had a lot of widgets and menus that were set up even though they
were not going to be displayed anytime soon. We were working on
evaluating whether X terminals could usefully be employed over a
V.32bis link, and this application could not: It took almost two
minutes from application launch for the window showed up, and users
(even the programmers who knew the program) were killing and
restarting the program over and over because their patience ran out.
On a 56kbps link, this would take about 45 seconds to start.
Uncomfortable but survivable. On the T1, about 3 seconds: No problem.

Most applications won't be this hungry. But you have to try it before
you know what YOUR applications will be like.

With a T1, you can load your X terminals over the link, and you can
painlessly remote-mount file systems. With a 56K, that is kind of iffy.

With a T1, you may consider getting a pair of drop/insert muxes and
pulling a couple of voice channels out, so that you can tie the PBXs
together and save a couple of outside lines. This may pay for the
increment in line costs.

> I'm also looking for suggestions for routers. I'm familiar (by
> reputation only) with cisco (or is it Cisco this week?). What else
> should I consider?

It is indeed Cisco these days. Cisco is the flagship of the industry,
enjoying the kind of name recognition that IBM used to have in
corporate computing. They are also enormously profitable, and have
adopted IBM attitudes. They don't participate in comparative
evaluations by magazines, and they don't participate in industry
interoperability test labs any more. I don't like that attitude.

There are about 50 manufacturers of bridges and routers in the market,
and most of them are okay for your application.

> Is bridging worth considering, too?

Yes. Your network management will be much easier with bridging: There
is just one LAN. Bridges are much less expensive.

> What should I look for in a good CDU/DSU?  Are the all the same, or
> are there large differences from manufacturer to manufacture?

CSU/DSUs are commodity items these days, and even different brands
usually work together. If you choose to mix voice and data on the
line, the multiplexer is the CSU (channel service unit) and the DSU
(Data Service Unit) is a channel card that plugs into the mux.

Don't buy the DSU until you have selected the router, because you need
to order DSU and router with matching cable interfaces. There are
actually about five standards for that connection. V.35 is becoming
the most common, though RS422 (MIL-188) is probably better. RS232 is
also often used for 56kbps.

One thing to look for in the DSU if you decide to multiplex is whether
the DSU card produces a "smooth clock" or a "gapped clock". Most DTEs
don't mind a gapped clock, but some do (although I have only seen
specific problems with video gear) and why invite problems.

Have fun. Did you go to InterOp to look at equipment? Next chance will
be in March in Washington, DC.

And no, the routers that my company makes, do not (yet) connect to
synchronous lines, so I am a somewhat neutral observer. There is,
however, a decent product made by another Santa Barbara company,
called Advanced Computer Communications.


Lars Poulsen, SMTS Software Engineer	Internet E-mail: lars@CMC.COM
CMC Network Products / Rockwell Int'l	Telephone: +1-805-968-4262	
Santa Barbara, CA 93117-3083		TeleFAX:   +1-805-968-8256