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From: mike@gordian.com (Michael Thomas)
Newsgroups: comp.dcom.lans
Subject: Re: DECserver multisessions through ISN
Keywords: DECserver LAT TD/SMP ISN multisessions
Message-ID: <127@gordius.gordian.com>
Date: 28 Mar 91 18:06:46 GMT
References: <1991Mar27.001042.283@bsu-ucs.uucp>
Sender: news@gordian.com
Reply-To: mike@gordian.com (Michael Thomas)
Lines: 57

In article <1991Mar27.001042.283@bsu-ucs.uucp>, d001ucsac@bsu-ucs.uucp
(Stephen P Kendall) writes:
> 
> I'm connected to a university VAXcluster through a DECserver 500 (which
> says it uses LAT V5.1) through an AT&T ISN network.  The ISN network is not
> a LAN in the usual sense; it connects to the terminal or PC through the
> COM port (19.2 kBaud) rather than through special network hardware.
> 
> The HELP menus on the DECserver mention an option to SET MULTISESSIONS
ENABLE,
> which then allows "multiple terminal sessions, each capable of a single LAT
> service session" through the "TD/SMP protocol".  This seems to imply that
> with a "session management terminal" or a PC running suitable software, that
> multiple simultaneous connections to the DECserver's services are possible.
> 
> I have found no further reference to this capability, either in the grey wall
> or the online docs.
> 
> My question:
> 
> 	1)  Is it possible to do this on a PC, given the hardware setup above
> 	(not on a true LAN-style network, but connected to the DECserver
> 	through a COM line)?
> 
> 	2)  If so, with what software?
> 
> --

  This is indeed a murky subject with the DECservers, but maybe this will
help. DEC's multiple session protocol (MSC) is intended to allow a "windowed" 
terminal to carry on conversations to multiple hosts through a single serial
port. These "sessions" are distinct from the DECservers LAT connections,
and really just spawn virtual jobs (sort of on the DECserver, really on the
LANtronix box) that "Autoconnect" to the desired service/host.
  Multisessions rides on top of the normal flow controlled line (either
XON/XOFF as in most DEC stuff, or RTS/CTS in other worlds) and only requires
the following:
	1) sacrosanct treatment of its control sequences which are of the
	   form: DC4(^T) MSC-command FS (^\)
	2) data must not be altered before it reaches the respective daemons
	   (ie insertion of NULL's or anything else is a no-no)
MSC is really a dippy network protocol with provisions for circuit creation,
deletion, session flow control etc.
  Theoretically *any* serial line could support MSC, PC or otherwise providing
it doesn't spew extranious stuff on the line. The only terminals that I'm 
aware of that support this capability are the VT330/340 and the VT420 as well
as some (but not many) of the DEC knockoffs. I am not aware of any PC based
package which deals with MSC but thats not something I ever look for. Such
a package would have to be front ended by some PROCOMM or Kermit like 
that deals with the terminal emulation problems. My guess is that since it
would require mutliple windows for the comm package, it probably doesn't 
exist since this would be a good deal of work (beyond just the MSC stuff).
  As for straight terminals off of your ISN network, there shouldn't be
any problem providing your net doesn't diddle with the bits as they go by.


			Mike Thomas @ Gordian