[ih] internet-history Digest, Vol 84, Issue 11

[Noel Chiappa]

    > From: Bob Braden <braden at ISI.EDU>

    >> I haven't read Nagle's thing, but that would also be interesting to
    >> look at, to see how much we understood at that point.

    > We were of course aware of Nagle's conclusions at the time, but I don't
    > think I actually read his RFC on congestion collapse until a few months
    > ago. It is well worth reading.

Indeed it is. Numerous gems; he probably understood the issues better than
anyone else, before Van. Some of them:

  Adding additional memory to the gateways will not solve the problem. 

How true! A lesson some people have just (re)-learned recently!

  the ICMP Source Quench message. With careful handling, we find this
  adequate to prevent serious congestion problems. We do find it necessary
  to be careful about the behavior of our hosts .. regarding Source Quench
  messages.

Interesting! This appears to be experimental data to support my thesis, that
SQ was not, in fact, fundamentally broken as a congestion signal - although
one has to use it properly, as he indicates (above), and here:

  Implementations of Source Quench entirely within the IP layer are usually
  unsuccessful because IP lacks enough information to throttle a connection
  properly.

Making the point that it was the congestion response mechanism _in TCP_ that
was lacking.

And finally this:

  All our switching nodes send ICMP Source Quench messages well before buffer
  space is exhausted; they do not wait until it is necessary to drop a
  message before sending an ICMP Source Quench.

which is again, a _very early_ recognition of things like today's congestion
bit, etc.


Alas, I'm afraid we probably didn't pay as close attention to his work as we
should have: John, if you're out there somewhere, my deepest apologies!

	Noel