-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of varun
Sent: Wednesday, March 14, 2007 2:19 PM
To: [email protected]
Subject: [Sip-implementors] Sip Registration and Invite forking

Hi,
Is contact header mandatory in SIP Registration.

No 
The TO header field being the address of record is
mapped to Contact address in Registrar when a
registration request is received.
In case, contact is optional then how is the mapping
done in Registrar?


No mapping is done in this case. A registration request can be received
to fetch the existing binding information ( It is called query like new
registeration, refresh, un-register, there is a query registration when
a REGISTER method is received without any contact information )


Another question is about Invite forking.How are the
forked Invite requests distinguished from each other
or rather their responses.

 
Forking requests are identified by the dialog-identifiers ( the from and
to tags ). For the case where there are multiple bindigns associated
with a DN and the call is forked by proxy/B2BUA, the call-id/session
identifier remains same, but the dialog-ids ( from-tag is populated
differently in the initial invite ). 
 
Now the responding UAS will populate different to-tag for each forked
INVITE request received by them. But the proxy/B2BUA based on the
call-id and tags can still figure out which session these responses are
associated with and in that session which dialog that response is
associated with.



Thanks
Varun




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