> It's also possible for DCCP to get a better initial estimate of the PMTU,
> and apparently there are other problems with the current DCCP PMTUD
> mechanism (using ICMP "can't fragment" messages).
Yes -- The current draft tries to make clear (but fails to) that a new,
PLPMTUD-style MTU discovery mechanism is acceptable. There are API problems
with such a scheme, but we absolutely allow it.
If you can accept an extra RTT or two at connection initiation time, I
think you can do pretty well:
Request -->
<-- Response
then, all in 1 RTT:
Padded Sync(512 bytes) --> /* actual #s would need to fit CC
Padded Sync(1280 bytes) --> mechanism */
Padded Sync(4000 bytes) -->
<-- SyncReply(1) /* SyncReplies sent only for those
<-- SyncReply(2) packets that got through */
<-- SyncReply(3)
> So, my question for the DCCP people, is it worth changing DCCP PMTUD?
It's certainly worth describing it better, and perhaps mentioning a set of
acceptable procedures. Have you any suggestions for useful procedures
here?
Eddie
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