section 9.1 of rfc 3261says - "The following procedures are used to construct a CANCEL request. The Request-URI, Call-ID, To, the numeric part of CSeq, and From header fields in the CANCEL request MUST be identical to those in the request being cancelled, including tags. 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. Using the same values for these header fields allows the CANCEL to be matched with the request it cancels (Section 9.2 indicates how such matching occurs). However, the method part of the CSeq header field MUST have a value of CANCEL. This allows it to be identified and processed as a transaction in its own right (See Section 17)."
truename <[EMAIL PROTECTED]> wrote: Hi all: There is a question confused me. In a session lanched by INVITE request, before replied a final status response, we can cancel this by a CANCEL request followed. Callid¡¢FromTag¡¢ToTag and Request-Url are enough to separate which INVITE request that the CANCEL request cancel. Why copy the number part of Cseq headfield? What is that surppose to? Here comes a example inferred by rfc3665: ----------------------------Callflow Start-------------------------------------------------------- Alice Proxy 1 | | | INVITE | |--------------->| | 100 | |<---------------| | 180 | |<---------------| | CANCEL | |--------------->| ----------------------------Callflow End------------------------------------------------------------ ----------------------------INVITE Message Start---------------------------------------------- INVITE sip:[EMAIL PROTECTED] SIP/2.0 Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70 Route: From: Alice ;tag=9fxced76sl To: Bob Call-ID: [EMAIL PROTECTED] CSeq: 1 INVITE Contact: Proxy-Authorization: Digest username="alice", realm="atlanta.example.com", nonce="ze7k1ee88df84f1cec431ae6cbe5a359", opaque="", uri="sip:[EMAIL PROTECTED]", response="b00b416324679d7e243f55708d44be7b" Content-Type: application/sdp Content-Length: 151 v=0 o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com s=- c=IN IP4 192.0.2.101 t=0 0 m=audio 49172 RTP/AVP 0 a=rtpmap:0 PCMU/8000 ----------------------------INVITE Message End---------------------------------------------------- ----------------------------CANCEL Message Start------------------------------------------------- CANCEL sip:[EMAIL PROTECTED] SIP/2.0 Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70 From: Alice ;tag=9fxced76sl To: Bob Route: Call-ID: [EMAIL PROTECTED] CSeq: 1 CANCEL Content-Length: 0 ----------------------------CANCEL Message End-------------------------------------------------- _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
