Subject: [Sip] Transport parameters & transport switching in GRUU-15

From: "Derek MacDonald" <[email-masked]>
Date: Sat, 17 Nov 2007 17:29:47 -0800

Hi Jonathan,

I recently implemented gruu-15 and it left me w/ a couple of questions about
GRUU generation.  Specifically, does the transport parameter used in the
contact
of the REGISTER message influence GRUU generation? Does the scheme?

The issue I see is that if you are using GRUU in an environment where NATs
aren't forcing the us of outbound, that automatic protocol switching as
defined
in 18.1.1 3261 could cause some odd behaviour.

For example if an UA switched to TCP because it was making a large
dialog-forming
request but used a UDP GRUU...bad things could happen w/ messages going back
to
the UA in the dialog.

I think this is easy to fix w/ two modifications/clarifications:

* a different scheme or transport paramter results in a different GRUU being
  generated for an AOR/instance-id pair
* a GRUU contact should still have a transport parameter. The examples in
  gruu-15 don't have transport parameteres on the GRUUs, but all of the
examples
  are UDP. Maybe this is a clarification instead of a change.

An alternative approach is to allow registration of multiple transports to
the
same GRUU, w/ the location server selecting which one to use. This seems
too complicated.

-Derek
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