What is important is that the Contact address *uniquely* identify the particular endpoint. If you are certain that there is exactly one contact addressed registed to your AOR then you could use it. But often that is not the case. If you have some other address that is unique to your endpoint you may use that.
There is a draft outstanding on GRUUs. (draft-ietf-sip-gruu-00.txt) Among other things, GRUUs are proposed for exactly the purpose you are asking about. You might want to read that draft, and consult the archives for related discussion.
Paul
prashant wrote:
Hi All, I have one question regarding value of contact header in 200 O.K response for INVITE. RFC 3216 states
" Contact contains a SIP or SIPS URI that represents a direct route to user agent, usually composed of a username at a fully qualified domain name (FQDN). While an FQDN is preferred, many end systems do not have registered domain names, so IP addresses are permitted. "
My question is whether contact header should be IP (or FQDN) address of UA, or it can as well be UA's AOR. In the later case, inbound proxy has to perform location service for in-dialog requests (like RE-INVITE) too.
Is it possible to use AOR in contact header for the purpose of hiding your IP address. But doesn't VIA header always carries IP address...and so at UAC side we need different approach (like NAT) to hide IP address.
Thanks in advance.
Regards Prashant
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