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SubjectRe: my broken TCP is faster on broken networks
   From: smurf@noris.de (Matthias Urlichs)
Date: 11 Sep 1998 23:24:59 +0200

> Congestion is not a temporary problem that can be fixed in such
> a simple manner. Even if every client does the backoff (hah!)
> there will be plenty of packets to which it does not apply.
>
... which is why the backbone routers now start doing the backoff algorithm
themselves: the more packets you send them without regard for proper
backoff algorithms, the more likely it is that _your_ packet will get
tossed.

Indeed, Van Jaconbson presented an insightful talk on this very subject
at an TCP implementors meeting at the IETF about 9-12 months ago. His
thesis was that now that the Internet is growing, our congestion
avoidance schemes which depended on everybody being polite was in danger
of falling apart. All aside from the Alan's point about humans hitting
the stop key on their browser and then resending their link, there is a
"tragedy of the commons" effect where implementors who break exponential
backoff win at the expense of people who obey the RFC's --- but if
everyone did this, the net would melt down.

One of his suggestions was to have the core routers enforce backoff, so
that the incentives for cheating would go away.

I don't normally follow the TCP implementor's working group (*), so I
don't know if they actually followed through on his suggestion;
Matthais's note seems to indicate that they did.

- Ted


(*) I only went because I heard that Van Jacobson was speaking, and he's
a truly wonderful speaker that can make the most subtle points about TCP
easy to understand. If you ever have an opportunity to hear Van
Jacobson speak, I'd strongly advise you to go and listen to him. You
won't regret it.


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