SUMMARY: Terminal Servers

From: Adam Shostack (
Date: Wed Oct 26 1994 - 10:59:31 CDT

        A few weeks back, I asked about SCSI based terminal servers
from Central Data Systems, and then followed up with a related
question on Magma & Aurora Sbus based terminal servers.

        Everyone with a Central Data System unit was pleased with it.
Some people went with Magma or Aurora because of price. (Magma &
Aurora sell Sbus based products.) No one seemed dis-satisfied with
any box. Which one to go with seems to be a matter of price,
reliability, and your concern about how easy it would be to move your
terminal server to a new system. One person suggested looking into
Xyplex, which sells a product that puts your terminal server on the
net. I want to be able to control logins more aggressively than that.
It might be possible to do this with the Xyplex unit, but it involves
lots of code. I prefer simple solutions; they're less prone to bugs.

        All the replies I got, including some sales stuff, are
available in (mbox format)

        Daniel Flax said that the Aurora drivers were slower &
couldn't compete with the CDS drivers. Syed Zaeem Hosain mentioned the
buffer in the CDS is much larger than in Magma's units, but also said
that his PC was able to keep up without the large CDS buffers.

617 272 8140 Xylogics ethernet
619 457 0750 Magma Sbus
617 290 4800 Aurora Sbus
800 482 0315 Central Data SCSI

        Robert Moyer ( sent a very nice summary of the
good & bad points of Central Data Systems, with some comparisons to
Sbus based units:

> Postives:
> 1) Scsi - makes it portable across most current Unix platforms, therefore if
> you have it hooked to a Sun today and move to HP a couple of years from
> now you can be assured of portability (unlike sbus or eisa solutions).
> 2) Easy to install and setup. Unlike network terminal servers that can
> require an advanced degree to setup properly, this takes minutes to
> install.
> 3) Tech. Support - basically a one man operation but very good and very
> responsive - can E-mail directly and expect a response in very short time.
> P.S. We ran into an unusal problem at our site where certain operations
> would cause a server crash. CD sent a consultant on-site to
> resolve the problem. The consultant worked after hours (midnight
> to 5 am) and managed to temporaily fix it by patching the driver
> source code. It turns out later that the problem was actually caused by
> a corrupted scsi driver in our AIX operating system but nevertheless
> Central Data really bent over backwards to help us out with this.
> 4) Flow Control - unlike other vendors who either only partially implement
> harware flow control or not at all, CD server support it on all ports.
> 5) Speed - The older models support up to 56 KB simultaneously on all ports,
> newer ones up to 115 KB.
> Negatives:
> 1) Can put a load on your scsi bus, if more than just a few terminals or
> modems are to be in use simultaneously than purchase a seperate fast
> scsi controller to dedicate to your scsi terminal server(s).
> 2) Dedicated System - if the system that your terminal server is attached
> to goes down then you lose access to the network. CD does sell a scsi
> switch that allows you to switch the server over to another running system
> but the switch is manual.


| as a much more flexible alternative, you should investigate the xylogics annex
| term server. 6172728140.
| the annex sits on the net, offers authentication to dialin and port servers by
| contacting a unix host's server daemon for username and passwd + a possible
| port passwd, offers ARA/PPP/SLIP/tty, remote consoles through port servers....
| etc. absolute balls.
| -heas

From: (Daniel M Flax)

> The Aurora I/O device consists of 2 parts, an SBus Card, and an
> external box that contains the ports. My experience has been that
> although the Aurora Hardware seems more robust and a better design
> (SBus vs SCSI) the Aurora software drivers can't compete with the CDC.

From: (Syed Zaeem Hosain)

| 5. The buffer in the Magma is 30 bytes long - in the Central Data unit,
| it is 1kb I think. However, I have not seen any problems with the Magma
| running full tilt at 115.2kbps to a serial port on an IBM PC (gave me
| 10,800 characters per second data rate for file transfers - as reported
| by Procomm Plus on the PC), so this may be a moot point.

Lastly, thanks to all the following for responding to my questions:

Alfred P. Balasco
Daniel M Flax
Dave Fetrow
David B. Brown
David Chavez
David Trueman
Ed Romascan
Jay Gallivan
John Bollard (twice!)
John DiMarco
John Lengeling
Kevin Sheehan {Consulting Poster Child}
Lisa Barnes
Mikael Johansson
Russ Poffenberger
Steve Ehrhardt
Syed Zaeem Hosain


"It is seldom that liberty of any kind is lost all at once."

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