> Is it mandatory or optional to send back 481 for a scenario > in which UAS doesn't know how to handle the transaction.
If you are still asking about CANCEL, the following snippet is applicable. RFC 3261 section 9.2: "If the UAS did not find a matching transaction for the CANCEL according to the procedure above, it SHOULD respond to the CANCEL with a 481 (Call Leg/Transaction Does Not Exist)." RFC 2119 section 3: "SHOULD This word, or the adjective "RECOMMENDED", mean that there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course." _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
