[Sip] GRUU-13 : algorithm in annex A.2 does not distinguish between multiple outbound contacts

Jonathan,

A minor remark about the temporary GRUU algorithm in A.2: if the UAC is 
using outbound and registers 2 Contacts under the same AoR and instance-id, 
the algorithm in A.2 currently cannot distinguish between those contacts 
(since the temporary GRUU only contains an index which resolves to an 
AoR+instance combination). Therefore, if the Contacts URIs are different 
(for example: different user part) the proxy is not able to reproduce the 
correct URI when rewriting the request URI.

Concretely: when a UAC registers e.g.
Contact: <sip:callee-001@192.0.2.1>
     ;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>"
     ;reg-id=1Contact: <sip:callee-002@192.0.2.1>
     ;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>"
     ;reg-id=2the proxy returns two distinct temporary GRUUs. However, 
regardless of which temporary GRUU the UA chooses to use, the proxy cannot 
determine whether to rewrite to "callee-001" or "callee-002"

This can easily be remedied, e.g. by including the reg-id in the mapping

Regards,
Jeroen 