[pcp] PORT_SET for application protocols other than SIP

[Simon Perreault <[e-mail]>]

During the meeting earlier today there was a question about whether any 
application protocol other than SIP could benefit from PORT_SET.

There were some replies to that question that involved the notion of set 
contiguity.

Contiguity has nothing to do with it. It's not because SIP likes to make 
use of contiguous ports that it would benefit from PORT_SET. It's all 
about optimization. A SIP UAS would be faster if it preallocated a bunch 
of ports instead of sending a PCP request each time it needed one. It 
could do that with individual MAP requests, but that would not be as 
efficient as a single PORT_SET for a number of reasons well stated in 
the draft.

I stand by my comment that it would be easy to imagine a protocol that 
would benefit similarly.

But I'll go further with a bold and daring example: PCP itself could 
benefit from PORT_SET. Imagine a back-to-back PCP server/client, as 
described in draft-cheshire-recursive-pcp. Imagine that it is very busy, 
handling many requests per second. It could benefit from PORT_SET by 
obtaining ports from upstream in big chunks. Then it would manage those 
chunks like port pools from which it would allocate to downstream 
clients. That could be more efficient than obtaining ports from upstream 
with individual MAP requests.

Simon
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