Subject: [Sip] SIP proxy and SIGCOMP

From: [email-masked]
Date: Mon, 6 Mar 2006 08:53:27 +0530

Hi,

I have a query relating to use of SIGCOMP in SIP, for which I could not find any info in the SIGCOMP related RFCs and drafts. If anyone has any info, kindly clarify this doubt.

In case a SIP proxy is forwarding a request based on DNS lookup (i.e. the called subscriber identified by the Request URI is not a subscriber of that proxy), then it will not replace the Request URI in the outgoing message. This is as per RFC 3261. However, what should be the behaviour in such a case w.r.t compression? How should the proxy decide whether or not to compress the outgoing message? Should it look for a "comp=sigcomp" param in the incoming ReqURI in order to make this decision? In case the callee had been a subscriber, this decision would have been made based on the presence of this parameter in the Contact header of the callee. This is specified by RFC 3486. However, RFC 3486 does not specify the behaviour when a proxy does not forward the request based on Contact header, but based on some other means, such as DNS lookup or statically configured routes, etc.

Any help would be appreciated.

Regards

Nagendra

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