More on TCP performance


Karl Auerbach (AUERBACH@CSL.SRI.COM)
Thu 1 Oct 87 19:56:50-PDT


Thank you all for all the comments.

It seems that if one can get a net with high enough bandwidth,
low enough error rate, and short enough delay, that TCP could, in
theory, consume a significant portion of the available bandwidth.

An example of the net that raised my initial question is the Los Alamos CP*
net which will run its links at 640Mbits/sec. Total capacity of the
net will be on the order of 20G (yes that's a 'G', not an 'M') bits/sec.
Lengths are short, so delays will probably be less than a few thousand
bit times (i.e. much less than a millisecond. The end nodes will be
Cray X-MP, Cray 2, and faster.

(At 640Mbits it only takes about 8 milliseconds to transmit a full
segment!)

What bothers me the most is that we've had HYPERchannels for a long
time and 80meg Proteon rings for a while, but the highest TCP
value I heard was about 17megabits. Why the discrepency? Is it something
intrinsic to the TCP protocol (and probably in ISO TPx as well) or
in the implementations or hardware?

                --karl--
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