Path: utzoo!mnetor!uunet!husc6!think!ames!aurora!labrea!decwrl!decvax!ucbvax!IU.AI.SRI.COM!KASHTAN
From: KASHTAN@IU.AI.SRI.COM (David L. Kashtan)
Newsgroups: comp.os.vms
Subject: Re: TCP/IP terminal servers on VAX/VMS
Message-ID: <571943081.0.KASHTAN@IU.AI.SRI.COM>
Date: 15 Feb 88 17:04:41 GMT
References: <8802102314.AA03147@bu-it.BU.EDU>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 32

Having been involved with TCP implementations for quite some time, I wanted
to get my 2 cents in...

I used to be a big supporter of the idea of off-board (separate processor) TCP
implementations.  It turns out that none of the "supposed" advantages of
these cards really pans out.  Usually the reason put forward for these boards
is that they offload the CPU.  You need to look very carefully at this -- there
are still some very significant communication costs to these boards (and the
VMS kernel still needs to do data multiplexing/de-multiplexing).  It turns out
that a good software-only TCP implementation will do just as well as the off-
board implementation.  The 2 TCPs for VMS that I have been involved in have
TELNET service that consumes no more processor than hardwired DZ-11 terminal
interfaces and they connect to the VMS terminal driver in standard way.

Both the aforementioned implementations are based on the 4.3bsd UNIX networking
code and any improvements made in the UNIX world (and, like it or not, that IS
where the major TCP work is being done) can be quickly imported to the VMS
world.  I don't know how the off-board processors are right now, but 6 months
ago (the last time I looked) they were all still running code based on 4.2bsd
which had MAJOR performance bugs.

Also note that off-board implementations can't act as gateways.

Sometimes you need to get special hooks into the network to do special things.
I have just completed a VMS NFS (Network File System) server that needed
special hooks into the network in order to get good enough performance
to act as a serious file server.  Try to do that with an off-board
implementation.

Don't dismiss the software approach,
David
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