Anshuman,
You are right , that's where i have a doubt too. for the Via header value for CANCEL and INVITE they differ in branch parameter value.Where i dont know if that should be same. What put me in doubt is , with CISCO MG it works!! but with pingtel is doesn't.So not able to figure out the right way to construct CANCEL message.

Regards
-venkat


Anshuman Rawat wrote:

Tadkot,

I think the problem is here --> ".... and insert it own VIA header field
value."

Section 9.1 of RFC 3261 states that -

"A CANCEL constructed by a client MUST have only a single Via header
field value matching the top Via value in the request being cancelled."

I am not sure about the branch parameter though (but my guess is that
should be the same too).

Regards,
Anshuman S. Rawat
Software Group,
Conexant Systems India Private Ltd.

-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
[EMAIL PROTECTED]
Sent: Friday, November 18, 2005 5:26 PM
To: Sip-Implementors
Subject: [Sip-implementors] CANCEL message construction at proxy level

Hi All,
I am new to this mail grpu and SIP world :). I need some information about how to construct the CANCEL message at the proxy level.
Scenario
1> Caller A sends  INVITE message to PROXY
2> PROXY(stateful) send 100 trying to caller A and sends the INVITE message to caller B
3> Caller A sends CANCEL message to PROXY to cancel the INVITE message
4> PROXY send 200 OK and 487 response back to Caller A and checks for 1xx response from caller B and construct the CANCEL message to send to caller B 5> PROXY construct this message with same Request-URI, TO , FROM, CALL-ID and Cseq number field values of the INVITE message send to caller B and insert it own VIA header field value. the branch id is different from the one which is sent in INVITE message to caller B. 5> But the CALLER B sends 481 Call/Transaction Does Not Exist message back to PROXY.

NOTE: if the CALLER B is CISCO media gateway, then it accept CANCEL message by sending 200 OK and 487 message, But if it is a Pingtel phone then it sends 481.

Any clue why the behavior is different here.

Thanks and Regards
-venkat



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