Hi Praveen, As per RFC 3261 section 8.1.1.7 Via and 9.1 its understood that
the matching happens if branch parameter in the request is equal to the one in
the top Via header field of the request that created the transaction, hence
branch parameter in the INVITE and CANCEL should be same. The branch parameter
value MUST be unique across space and time for all requests sent by the UA.
The exceptions to this rule are CANCEL and ACK for non-2xx responses. As
discussed below, a CANCEL request will have the same value of the branch
parameter as the request it cancels.
9.1 Client Behavior
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).
Regards,
Kavitha.Menneni
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