Re: my broken TCP is faster on broken networks

Gregory Maxwell (linker@z.ml.org)
Fri, 11 Sep 1998 18:26:05 -0400 (EDT)


On Fri, 11 Sep 1998, Albert D. Cahalan wrote:

> > 2 minute delays are fine in bulk traffic. You whole thinking is broken
> > however.
> >
> > If n users * x packets with 2 second rtt simply dont fit down the pipe in
> > question you lose.
> >
> > Chunks of the net are congested. That congestion however you will
> > note doesnt cause a congestion explosion
>
> You are completely ignoring several important things.

Yes, but Alan is most likely ignoring them intentionaly.

> 1. It's not all TCP/IP. There are many protocols without backoff.
> If the TCP/IP connections do the backoff, other protocols will
> have an advantage and will consume all bandwidth. TCP/IP won't
> get a fair share by being polite.

This is why CBQ exists. As more routers impliment this, their situation
will be resolved.

> 2. The exponential backoff can not be enforced, since users can
> restart the connection. That is exactly what happens.

This however, IS a real problem. Not to mention that the connection open
takes a bunch more packets. Big waste.

> 3. The last time I heard, http was the #1 protocol. Since the
> connections are short-lived, backoff works poorly anyway.

Http is misdesigned. It should have been impliempted on top of UDP with
approiate application measures of congestion control and data integreys.

Wouldn't it be great to have a lossy image format that can be sent over
udp, where the image quality is related to your line speed and packet
loss?

>
> Look, this is dumb:

Http is dumb.

> 1. user clicks on a hyperlink
> 2. backoff takes effect
> 3. user clicks "Stop" and tries the link again, sending MORE packets
> 4. congestion explosion, as every user does the above many times
>
>
> That is what really happens. Maybe you'd like to get rid of that
> damn human. Humans mess up the math. Proofs that don't consider
> human behavior are WRONG.

They are not wrong, they just dont show the current state of affairs. If
http used UDP then things would be alot better.

> It may seem evil to reduce the backoff. It is far worse to have
> behavior that makes those awful humans restart the connection.
> I've not seen anyone really address real-world human behavior.
> Networks do not exist all alone without humans.

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