Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!topaz.rutgers.edu!ron
From: ron@topaz.rutgers.edu (Ron Natalie)
Newsgroups: comp.dcom.lans
Subject: Re: Terminal servers over ethernet?
Message-ID: 
Date: 5 Jul 88 22:38:51 GMT
References: <320@ucrmath.UUCP>  <3960@saturn.ucsc.edu>  <9816@e.ms.uky.edu> <23612@bu-cs.BU.EDU>
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 38

> A networked terminal, in my experience, must always support flow
> control, even at speeds as low as 1200 bps.  I have never been able to
> make a device that did not support flow control operate over a
> terminal server.  Contention and lost packets...

I have a Visual 200 on my desk which is as dumb as they come.  It doesn't
need anytype of flow control.  Contention and lost packets have little
to do with it.  If you're talking about Ethernet there's more than
enough bandwidth.  Your statements are also a bit confusing.  No body
types at even 120 cps, so the flow control that is really necesary
is at the host end.  With TCP the server <-> host flow control is all
ready managed by the TCP window.

> I would be concerned on large model servers like the cisco.  What
> happens if everybody is active at the same time?  Do all 96 terminals
> operate at 9600 bps average throughput?

Large model servers usually have larger scale processors.  For example
the CISCO terminal server runs a 68020 while most of the smaller ones
use 8086's or 80186's.  We don't expect our CISCO terminal servers to
run 96 lines at 9600 all active, but we do expect them to run 64 and
we haven't been proved wrong yet.  The answer is that they get slower
when you overload them, but of course, that makes less of an argument
that the terminal needs flow control, not more.

> There is work on SLIP support on terminal servers, although BU isn't
> running SLIP yet.  I wonder how many SLIP ports a typical terminal
> server could support?  Is SLIP more compute intensive than telnet?

CISCO has SLIP, such that it is, on their servers.  I can't tell
you for sure but my guess is that while SLIP is more I/O intensive
(theres actually protocol overhead running in both directions and
if you have more than just a PC on the far side you've probaby got
more than one connection going at a time), however compute intensity
will be less.  You're not using the TCP part of the server, you're
just dumping IP packets into the IP portion directly.

-Ron