Path: utzoo!utgpu!jarvis.csri.toronto.edu!me!radio.astro!helios!root
From: root@helios.toronto.edu (Operator)
Newsgroups: comp.dcom.lans
Subject: Re: Request For Opinions:  Terminal Servers vs. Dataswitches
Message-ID: <756@helios.toronto.edu>
Date: 31 Mar 89 21:58:59 GMT
References: <4748@charon.unm.edu>
Reply-To: sysruth@helios.physics.utoronto.ca (Ruth Milner)
Organization: University of Toronto Physics/Astronomy/CITA
Lines: 47

I'd go with the servers. There is a cheap (nearly free) version of TCP/IP
available for VMS. I've forgotten the details, but it's the Carnegie-Mellon
implementation. You can probably get more details about ordering, etc.
off the comp.os.vms list (AKA info-vax on BITNET). The big advantage is
that an awful lot of new systems, in particular *everything* using any
flavour of UNIX, will already come with TCP/IP, and with the servers
you can immediately connect over the network without having to add extra
hardware to the new system. If you stick to data switches, everything you 
ever install from now on (and all the existing systems) will have to have 
serial lines put into them. If you are talking about uVAXes or VME-based 
systems, you can use up a lot of valuable slots this way. We have found
that there are just too many other things we want those slots for. Memory
and disk controllers, for example. If you're going to be putting the
Ethernet in for networking anyway, you might as well take advantage of it.

Other advantages of servers are that a single person can connect to a
number of different machines at the same time, and easily move between
connections with only a few keystrokes. The serial switches I have seen
sometimes allow this, but it isn't nearly as easy. TCP servers, like switches,
can be connected to devices like modems and accessed from the CPU for
dialout. Also, when you need to increase the number of lines available
to users, with servers you just plug another one in (in areas of high
concentration you can use a DELNI or similar to reduce Ethernet tapping).
If your Ethernet is thickwire or you have a DELNI, you don't need to
disrupt the rest of the network to install a new server, whereas putting
new boards into a serial switch system often involves powering down at
least a portion of the other lines. You can also put the server close to
the area where the lines are needed, thus reducing wiring, which can't
always be done with switches (that's assuming that your Ethernet isn't
just contained in the machine room; most aren't).

We gave up on serial lines a long time ago. We have been using DECservers
for access to our VAxes and have recently begun to install TCP servers.
Eventually we hope to have all our DECservers replaced with another brand
capable of doing both LAT and TCP. There are several of this type of server
available now. We have over 200 lines available to users, with direct access 
to either 8 VAXes or every TCP/IP machine on campus (a couple of hundred). I'd
hate to think what the wiring would have looked like to set that up with
serial switches.

Standard disclaimer: this is me expressing my opinions, although obviously
in this case they coincide with those of my bosses, who pay for the equipment.
-- 
 Ruth Milner          UUCP - {uunet,pyramid}!utai!helios.physics!sysruth
 Systems Manager      BITNET - sysruth@utorphys
 U. of Toronto        INTERNET - sysruth@helios.physics.utoronto.ca
  Physics/Astronomy/CITA Computing Consortium