Subject: [Simple] RE: MSRP: Towards closure on HoL blocking issue

From: Adam Roach <[email-masked]>
Date: Mon, 28 Apr 2003 17:27:19 -0500

Paul Kyzivat writes:

> Also, your proposal would (I think) mean that the
> eventual chunking solution would require a response
> for every chunk. I think that could end up making file
> transfers inordinately expensive.

Ummm... With the size of MSRP responses, you'd end up with
something like 0.25% of the volume of the sent messages
in the reverse direction to confirm chunks. I don't think
"inordinately" means what you think it means.

> This whole HOLB thing is because we are trying to address use 
> cases that might better be addressed by a file transfer
> protocol. We had better decide how important a use case this
> is.

It DOESN'T MATTER how important it is as a use case.
Ignore it as a use case. Treat it as a DOS attack.
Unless we address it, it IS a DOS attack. Just
saying, "that's not what MSRP is meant for" will
NOT stop people from doing it -- including people
who want to do it maliciously.

/a
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From: Ben Campbell <[email-masked]>
Date: 28 Apr 2003 17:33:02 -0500

> who want to do it maliciously.

I would think that a DOS attacker would simply ignore restrictions that
say how many outstanding transactions you can have at once. So for this
to be helpful against attackers, the relay has to _enforce_ the limit.
How would you enforce it? Forcing a relay to be transaction stateful for
SEND requests?

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From: Paul Kyzivat <[email-masked]>
Date: Mon, 28 Apr 2003 21:50:54 -0400

> "inordinately" means what you think it means.

My concern isn't with the size of responses - it is with the latency. It 
is a sort of vague concern at the moment because we have a lot of 
alternatives under consideration, and hypotheticals for chunking that 
aren't even under consideration.

But I will grant that this may turn out to be a bogus concern.

> who want to do it maliciously.

Sure, but it greatly affects what *kind* of a solution we adopt.

We could say that sending anything bigger than 1k should be considered a 
file transfer problem, and that it should be handled via another 
protocol. Then we wouldn't have a HOLB problem.

And we could have a very simple flow control solution then too. One or 
two messages in transit, based on the end-end response would be ok if 
all we were addressing was interactive chat.

Solutions to both the HOLB problem and flow control get more complex 
when the requirements are more demanding.

	Paul