Hi, As per 9.1 Client Behavior of RFC 3261
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. If my understanding is correct, even if the INVITE being cancelled has already been responded to by a 1xx with a to-tag, the CANCEL will have no to tag. However, I have seen implementations that send a CANCEL with a to-tag if the call is already in early dialog state. I have also seen UAS silently discarding CANCELs without to-tag if it comes in early dialog state. This makes me doubt my original understanding of the RFC. Can anyone shed some light? Joegen _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
