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From: lamaster@ames.UUCP (Hugh LaMaster)
Newsgroups: comp.protocols.tcp-ip
Subject: Re:  Ethernet Terminal Concentrators
Message-ID: <1484@ames.UUCP>
Date: Fri, 8-May-87 12:35:05 EDT
Article-I.D.: ames.1484
Posted: Fri May  8 12:35:05 1987
Date-Received: Sat, 9-May-87 19:01:41 EDT
References: <8705071949.AA23126@ucbvax.Berkeley.EDU>
Reply-To: lamaster@ames.UUCP (Hugh LaMaster)
Distribution: world
Organization: NASA Ames Research Center, Moffett Field, Calif.
Lines: 42


In article ... SYSTEM@CRNLNS.BITNET writes:

>
>The problem that we've encountered is the high
>CPU overhead used by at least one TELNET implementation under VMS.
>The following is a report of a test done using CMU/TEK TCP/IP

:

>CMU/TEK TCP/IP software uses an excessive amount of cpu resources

>2 VAX-11/750s (LNS53 and CLE750) with FPA and 5 Megabytes of memory,
>running VMS 4.4 and connected with DEUNA Ethernet interfaces.

>The transfer used 100% of the cpu on (remote) CLE750
>                  ====
>(20% kernel, 80% user, <5% interrupt)
>
>User mode programs on on CLE750 were the TELNET server using about 50%,
>IP_ACP using about 15%, and TYPE using about 15%.



One part of the results surprised me, based on my experiments.  I have
performed essentially the same experiments, using Wollongong TCP/IP on VMS.
a terminal uses about 5-6% in user state.  However, during the same period,
total system usage (user + interrupt + kernel) was about 15%.  This was true
with both telnet and a direct wired terminal.  Two points:  1)  Wollongong
TCP/IP is clearly more efficient than the TCP/IP you used; and 2)  I saw
higher overhead from direct wired terminals than you did (I am wondering why
right now :-)  ).  Anyway, I was concerned about telnet overhead myself, but
found no observable difference between network and direct wired.  This
surprised me, I admit; Wollongong has improved a great deal in the last
releases.

An interesting part to me was discovering just how expensive terminal I/O is
on VMS.  7 9600 baud terminals at full output saturated a 785...
I think it is definitely a question which should be addressed more
carefully by the terminal server vendors.  Some implementations work
fine, others seem to be a problem.  Most of the vendors don't seem to
have looked at this as carefully as I would have expected.