[e2e] Are we doing sliding window in the Internet?

David P. Reed dpreed at reed.com
Mon Jan 7 06:46:10 PST 2008

99% of the effect of the original TCP congestion control "innovation" 
was due to a simple and robust principle: when a packet is lost, cut the 
traffic being sent *drastically*.   This converted a tendency of the 
community to turn packet losses into a positive feedback loop of 
retransmission into a shared understanding that "positive feedback loops 
are bad".

That was a community-scale learning that was useful.

I would argue that the idea that TCP is now "near perfect" as a standard 
that *must be enforced lest the Internet enter congestion collapse* has 
almost no real-world evidence.

In fact, very little of the traffic on the network today comes in the 
form of end-to-end unbounded-rate-demanding streams.   TCP's congestion 
control (and the definition of "TCP compatible" fairness, too!) is 
"tested" only for such a trivial case.   No One At All tests TCP 
congestion control in a world of HTTP, VoIP, streaming video from 
YouTube, Skype, etc. The "gurus" of the IETF that study protocol 
*documents* have intuitions that are seriously flawed, if only because 
they don't actually have any data about the traffic ANYWHERE in the damn 
network.   (kc claffy would die to have such data).

So it seems that a bunch of self-elected high-priests of IETF have taken 
it upon themselves to claim God-like, experiment-free knowledge of the 
Internet as it really is, and to use that knowledge to claim that TCP is 
the Gold Standard that must be obeyed lest the network finally do what 
Bob Metcalfe erroneously said it would do and ate whatever piece of 
clothing he ate as a result.

Do science and real engineering, please.   Yeah, the AIMD algorithm in 
TCP saved the Internet's ass.  But it is not Holy Writ.

More information about the end2end-interest mailing list