> An explicit passage in the RFCs is missing (or I didn't find it) > which says UAS hat to response or don't has to.
RFCs typically don't go into exhaustive detail concerning the processing of malformed messages. If the UAS considers the From's URI to be malformed, they'd likely consider the 400 response to also be malformed if they built/sent it. Thus they may have chosen to avoid sending a malformed response. They potentially would behave the same way if other mandatory headers were missing/malformed and would impact the ability to build a valid response. The following snippets are from RFC 3261. Section 8.1.1: "A valid SIP request formulated by a UAC MUST, at a minimum, contain the following header fields: To, From, CSeq, Call-ID, Max-Forwards, and Via; all of these header fields are mandatory in all SIP requests. These six header fields are the fundamental building blocks of a SIP message, as they jointly provide for most of the critical message routing services including the addressing of messages, the routing of responses, limiting message propagation, ordering of messages, and the unique identification of transactions." Section 8.2.6.1: "The From field of the response MUST equal the From header field of the request." Section 19.1.2: "- Any uri-parameter appearing in both URIs must match." "- A user, ttl, or method uri-parameter appearing in only one URI never matches, even if it contains the default value." _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
