[Standards] Stanza Size Limits

Justin Karneges justin-keyword-jabber.093179 at affinix.com
Thu Sep 4 16:34:18 UTC 2008


On Thursday 04 September 2008 08:11:04 Dave Cridland wrote:
> On Thu Sep  4 15:30:53 2008, Peter Saint-Andre wrote:
> > Gosh, do we really need all this complexity? Negotiating per-user
> > limits seems unnecessary to me.
>
> Not per-user. Kevin means, I think:
>
> C1 <--C2S:MTU=1000--> S1 <--S2S:MTU=800--> S2 <--S2C:MTU=500--> C2
>
> All C1 knows is that a stanza is allowed to be 1000. S1 thinks it can
> be 800. How does C1 decide that to send to C2, it needs to send an
> MTU of 500? Or at least, how does it do this without PTMU, which'd
> suck quite a bit?

Finding the MTU over XMPP ought to be easier than it would be over IP.  
Probably it's enough for C1 ask C2 what its maximum receive size is.

This works, because C2's limit needs to be the same as S2's limit (in the 
S2->C2 direction).  And the C1->S1 limit should be known by C1.  Therefore, 
C1 just needs to send stanzas smaller than the C1->S1 limit (which it knows) 
and the S2->C2 limit (which it queried C2 for).

The S1->S2 limit would need to be equal to or in excess of the S2->C2 limit.

> And two questions of my own:
>
> What is the optimal size for a stanza?

We don't seem to know, which is part of why I brought this up.

> Why doesn't it depend on contention of the XML stream?

Explain.

-Justin



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