SUMMARY: Ethernet modem pooling and UI

From: CB Francois - NYC SE (
Date: Thu Jan 24 1991 - 19:08:26 CST

Thanks to all of you who took the time to answer my query. I believe I
got most of your replies. A few might have gotten lost in my mail file
debacle, so I thank those of you whose names don't appear below. And a
special mention to those of you who took the trouble to write to me a
second time. My apologies for taking so long to summarize.

Part of my original request:

>I'm currently looking for any products out there that would enable me to
>establish a nicely distributed modem pool to provide basic dial-in and
>-out services to a network of SPARC workstations.

>The ideal set-up would involve 1) a device on the Ethernet with support
>for numerous serial ports for modems, and 2) workstation-side software
>(akin to PC products such as PROCOMM, XTALK, RELAY) that would present
>a nice X-based (tty would also do) interface to such things as dialing
>directories, auto-dialing, login scripts, some minimal emulation (VT,
>ANSI), and basic file transfer mechanisms.

On the hardware side, the results were decidedly mixed, with "terminal"
servers (though no one in particular) emerging as the choice for most
respondents. The names mentioned include Cisco, Xylogics, Xyplex (same
box?), along with the Telebit Netblazer I had asked about.

The software issue invited only two suggestions, both of which bear
further exploring. One, 'expect', is not specifically related to the
modem issue but sounds pretty powerful all the same. All I know about
the other is its appetizing name 'pcomm'.

So here are with a few minor edits and comments the bulk of your replies.


[First, the most intuitive approach: -Ed.]

From: (Neil Gorsuch)

As far as adding a bunch of modems, why not do things the easy way and
add them directly to the sparcstation(s)? We have a SCSI based
multiplexer that now supports full dial-in/dial-out on each line, uses
the tty drivers already resident in Sunos, and required no new drivers
or kernel rebuilding. This way, just have people log in on whatever
machine the modem happens to be attached to (I would assume that you
would use NIS to make it the same everywhere), and let one or more
servers provide actual home directories through NFS. Then you can even
do some level of load balancing via how many ports you connect to each
machine. It would also be a simple matter to write a program that
front-ends for getty or login and switches them to an rlogin on
whichever machine is the lightest load at that point. And of course,
have all machines update their /usr/hosts all the time so that people
could switch to another machine simply by typing the machine name.


[The terminal server proponents:]

From: (Peter Gutmann)

For the connection of a bunch of modems to the ether I would choose a
terminal server. This gives you a single point of connection and the
individual ports can be dedicated to talking to a particular machine.
In addition ports can be designed to support slip and other protocols

From: (Angel R. Rivera)

[In reply to my question about the NetBlazer's suitability for the job:]

Yes it does. Why do you not contact them? You can get them at:

[In the past, has worked for me. Here's a blurb
 about the Netblazer I found in the January issue of SunExpert:]

_Dial-up TCP/IP Router_

"The NetBlazer automates modems' connection establishment over the
public-switched telephone network, linking remote TCP/IP-based
Ethernets. The product saves users the cost of leased lines, while
offering the flexibility of dial-up.

"NetBlazer performs functions such as automatic modem configuration,
automatic call establishment and authentication, automatic line
disconnection (when it has been idle for a predetermined length of
time), automatic bringing up or dropping of parallel modem lines in
response to line traffic, and automatic control of dial destination
limitations (on a per-user basis).

"NetBlazer offers users three levels of security, multivendor
connectivity and on-board SNMP network management software. It
supports the following protocols: TCP/IP, UDP, ICMP, RIP, SLIP, PPP,
FTP, Telnet, Ping, Finger, Echo and the Domain Name Service. The
product supports up to three Ethernet 802.3 interfaces, up to 26
asynchronous RS232 connections to modems or terminals, and one optional
V.35 synchronous connection to a 56K-bps leased line. [A bit more than
I need, but you have to hand it to them...]. Prices begin at $2995,
not including modem."

From: (David LeVine)

What we are doing is using a Xyplex terminal server as a modem server.
These boxes speak both IP and LAT so when a user calls in, he/she can
connect to the IP or Decnet node of choice. The Xyplex sits on the
ethernet so when you call in you can get anywhere else on the net from
there. It also accepts telnet/LAT sessions so that you can connect to
it in order to dial out. I'm not sure that standard tip-type programs
will work as expected (we're still in the process of setting this up),
however, you can definitely get to the modems for dialing out. I would
stay away from Sun's ALM type hardware as we have experienced a
multitude of problems driving modems off of them [oh..? :-)]. The
Xyplex boxes provide standard vtxxx emulation and I believe that the
latest version of the software even supports tn3270. I'm confident
that scripts can be generated to make most if not all of this invisible
to users.

From: (Albert Cheng)

Our site used the Terminal Server from Cisco. It lets you connect up
to 32 modems per box and a user may dial in and then connect to any
machine on the network.

You can dialout from it too.

From: (Kevin McMahon)

Sounds like you want a terminal server. You can get an Annex box from
Xylogics (617) 272-8140. I believe Cisco also makes them.


[Some software ideas:]

From: (Don Libes)

We use 'expect' to do exactly the things you describe. You can hide a
lot of ugliness with it. It's public-domain. Here is an excerpt from
the README file.

This is the README file from "expect", a program that performs
programmed dialogue with other interactive programs. It is briefly
described by its man page, expect(1). More examples and further
discussion about implementation, philosophy, and design are in
"expect: Curing Those Uncontrollable Fits of Interaction" by Don
Libes, Proceedings of the Summer 1990 USENIX Conference, Anaheim, CA,
June 11-15, 1990. Even more examples and discussion, specifically
designed for system administrators, are in "Using expect to Automate
System Administration Tasks" by Don Libes, Proceedings of the 1990
USENIX Large Systems Administration Conference (LISA) IV, Colorado
Springs, CO, October 17-19, 1990.

Design and implementation of this program was paid for by U.S. tax
dollars. Therefore it is public domain. However, the author and NIST
would appreciate credit if this program or parts of it are used.

expect may be ftp'd as pub/expect.shar.Z from
Request email delivery by mailing to "". The
contents of the message should be (no subject line) "send
pub/expect.shar.Z". Once you have retrieved the system, please read
the INSTALL file. The papers mentioned above can be retrieved
separately as pub/ and pub/


You might want to check out pcomm from a comp.sources.unix archive.


That's all folks. If any of you would like to add to the above suggestions,
I'd be more than happy to summarize again. Meanwhile, my heartfelt thanks
for helping out.


Charles [B. Francois]        (212) 558-9119        cbf@gotham.East.Sun.COM

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