The CANCEL request cancels a pending request with the same Call-ID, To, From and CSeq (sequence number only) header field values, but does not affect a completed request.
A user agent client or proxy client MAY issue a CANCEL request at any time MAY choose to send a CANCEL to
destinations that have not yet returned a final response after it has received a 2xx or 6xx response for one or more of the parallel-search requests. A proxy that receives a CANCEL request forwards the request to all destinations with pending requests.
A user agent client or proxy client MAY issue a CANCEL request at any time MAY choose to send a CANCEL to
destinations that have not yet returned a final response after it has received a 2xx or 6xx response for one or more of the parallel-search requests. A proxy that receives a CANCEL request forwards the request to all destinations with pending requests.