[Sip] SIP instance identifiers

[Jonathan Rosenberg <[e-mail]>]

Folks,

We have three drafts this round that all propose a way to define an 
instance identifier for a UA:


http://www.jdrosen.net/papers/draft-ietf-sip-gruu-01.txt
http://www.ietf.org/internet-drafts/draft-jennings-sipping-instance-id-00.txt
http://www.ietf.org/internet-drafts/draft-stucker-sip-guid-00.txt

all three are similar. Mine uses a contact header field parameter, and 
uses the callee capabilities framework to enable caller preferences 
routing based on instance iDs. Cullen also uses a contact parameter, but 
not within the callee caps framework. Brian defines a header field.

I think we generally understand the requirement here, though it would 
probably be good to obtain use cases to be sure. The design choice is 
where to include this parameter, and this represents the difference 
between the three approaches.

I tend to prefer a Contact URI parameter over a header. My main reason 
for that is REGISTER requests. If a register request has multiple 
contacts, which contact does the instance identifier apply to? As a 
header field, it would be hard to know. If you make it a contact header 
field parameter, its no problem. Those header field parameters could 
also then be used in the Contact in INVITE/200 SUB/NOT, etc.

Then, the question is whether to use a regular Contact header field 
parameter as Cullen has done, or a callee cap parameter as I have done? 
The callee cap approach allows for caller preferences to be applied to 
routing to a specific instance. Now, a good question is whether such a 
thing is needed or even a good idea, if we have GRUU as the ideal way to 
route to a UA instance. I can go either way, but welcome thoughts on the 
topic.

Thanks,
Jonathan R.
-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
[e-mail]                     FAX:   [phone]
http://www.jdrosen.net                      PHONE: [phone]
http://www.dynamicsoft.com


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