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- Path: sparky!uunet!zaphod.mps.ohio-state.edu!news.acns.nwu.edu!telecom-request
- 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
- Message-ID: <telecom12.861.7@eecs.nwu.edu>
- Organization: CMC Network Systems (Rockwell DCD), Santa Barbara, CA, USA
- Sender: Telecom@eecs.nwu.edu
- Approved: Telecom@eecs.nwu.edu
- 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
- Lines: 94
-
- 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
-
-