North American Network Operators Group

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Re: MTU of the Internet?

  • From: Paul A Vixie
  • Date: Sun Feb 08 01:02:22 1998

> There is, however, the spectre of there being so many SYNs
> flying around that they alone might cause congestion
> collapse.  I dunno if I should be frightened of that or
> not, but I am not one of your origin server friends. --:)

i'm not worried about the syn's so much as i am worried about the lack of
interstream resource planning.  in all of the popular desktop stacks, a new
tcp stream does its own slow start (not paying any attention to the aggegrate
bandwidth*delay when several streams are open to the same origin server).
this means every new tcp session has to sense the available bandwidth*delay,
causing the other tcp sessions toward the same origin to have to back off
and try to find the new equilibrium.  and then, wonder of wonders, it's time
to close all of those connections because the user has clicked "stop" after
getting bored waiting for thos GIFs to populate, and has clicked on something
else, so let's start this whole stupid process over again with some other
origin server.

persistent http helps this a little.  aggregation through proxies -- even if
no caching is done -- will help it a little more.  t/tcp would help some.
desktop tcp stack fixes to remember end-to-end bandwidth*delay between
connections, and to treat end-to-end bandwidth*delay as an aggregate to be
shared between simultaneous connections from/to the same place (or to just
stop doing that stupid parallelism in favour of one http/1.1 persistent
connection) would also help.

> Finally, could your explain the "benchmark" comment a bit?

this was in specific reference to my product's connection quota for each
origin server, and the fact that if we intercept too many simultaneous
connections to a given origin server, we just delay the ones for which no
open connection is available.