[Info-vax] terminal servers etc

[David Froble]

Phillip Helbig---undress to reply wrote:
> I would like to connect some real terminals far away from my cluster to 
> a LAT service on the cluster so that I can hit RETURN on the terminal 
> and one of the nodes will offer the login prompt.  If I have the basic 
> idea correct, I can connect the terminals to a terminal server via a 
> serial connection then connect the terminal server to the LAN where it 
> can talk to the cluster via TCPIP or LAT.
> 
> I've used a similar setup, years ago, but have no idea how it was set 
> up.
> 
> Speed is not an issue since I can't type much faster than 100 b/s.  :-)
> 
> Some questions (note: I'm not looking for actual instructions; I'll look 
> them up if I decide to go this route):
> 
> How difficult is this to set up on the VMS side?
> 
> Is LAT preferable (easier, better) than TCPIP?

Not hard, but you need to know the proper commands.  Some older terminal 
servers are LAT only.  Later ones may include TCP/IP.  Frankly, between 
the 2, I think LAT has less overhead.  That's what I use/used when i had 
terminals.  Now everything is weendoze PCs using a Telnet client.

> I have stuff like DECserver 90TL, DECserver 90M.  Will this do what I 
> want?  (I also have some DECserver 200MC and 250 but I assume the 90s 
> are the better choice here.)

The 90TL needs a MOP load from a host.  The 90M has memory in the unit 
that stores the operating system and does not need a load from a host.

> The DECrepeater 90T is functionally equivalent to a 10 Mb/s hub (but
> amplifies the signal, hence a repeater and not a hub), right?

Correct

> T is TCPIP, L is LAT, TL is both, M is both and more?  Since a hub or 
> repeater is essentially a dumb device, why can't it handle all protocols 
> as long as the wiring is correct?

Well, I've never wondered about what the letters stood for.  You may be 
correct, or not.  The 90L+, 90TL, and 90M are all terminal servers.

Don't know what you mean by "all protocols".  The 90T is an ethernet 
repeater.  As far as I know, it doesn't get into protocols such as LAT 
and TCPIP.  It just moves ethernet packets, or whatever.

> Is the only network connection on the server the BNC coax connector?  If 
> so, I'll probably need one of the repeaters in order to connect this to 
> a twisted-pair network.  I have both standalone server and repeater as 
> well as some which connect to a backplane (and have the backplane as 
> well).  Will the backplane provide a network connection between server 
> and repeater?  (If so, I might be able to avoid BNC.)
> 
The DEChub 90 stuff is well dated, as you could guess with 10baseT. 
They are from a time when thinwire ethernet was still in use.  The 
backplane (as long as you can keep the power supply working) takes a 
thinwire cable (without the "T") on the side, and connects that and all 
modules plugged in together.

The power supply is noisy, and collects dust.  You'll need to clean it 
periodically.  It will power all modules plugged into the DEChub90.  If 
you connect the 90T to your twisted pair network, then all modules in 
the DEChub will be connected.  Rather nice, but dated, functionality, 
like much DEC gear.

I have maybe 4-5 backplanes (DEChub90) but only one power supply still 
working.  (Excess inventory free to a good home.)  I use the DEChub to 
connect the older systems which use thinwire.  I could use AUI to 
twisted pair adapters, but either gets the job done.  Regardless, it's 
all 10 mbit.