Because the ACK is an independent transaction and the contact is a pure IP address, the transport layer for ACK must be UDP (see RFC3263).
If the user agent would like to be reached via TCP, it should put in the contact the transport=TCP. Christian -----Urspr�ngliche Nachricht----- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Gesendet: Montag, 17. November 2003 19:32 An: [EMAIL PROTECTED] Betreff: [Sip-implementors] SIP over TCP We have a discussion about "optional or mandatory" in relation to the tag "transport=tcp" in the contact header and the meaning of TCP in the VIA header. In RFC2543 and 3261 there is no clear message how it should work. Exactly: Is the "transport=tcp" tag in the contact field always mandatory if the optional header field "Contact" is used. The underneath transaction is done in one TCP connection and it is working with most of end devices. But one end device is switching back to UDP for the ACK message because there is no "transport=tcp" at least in the 200 OK message. Is this behaviour correct if each message indicates TCP in the VIA field ? Example: Following trace is a example how it works at the moment. But one provider of end devices says this is incorrect, because transport is mandatory. INVITE sip:[EMAIL PROTECTED] SIP/2.0 Via: SIP/2.0/TCP 172.31.9.165:5060;branch=z9hG4bK3608975509 From: <sip:[EMAIL PROTECTED]>;tag=2216986771 To: <sip:[EMAIL PROTECTED]> Call-ID: [EMAIL PROTECTED] CSeq: 1 INVITE Contact: <sip:[EMAIL PROTECTED]> Max-Forwards: 1 Content-Type: application/sdp Content-Length: 169 v=0 o=2_0 1064518837 1064518837 IN IP4 172.31.9.165 s=SIPa Session c=IN IP4 172.31.9.165 t=0 0 m=audio 7080 RTP/AVP 8 a=rtpmap:8 pcma/8000/1 SIP/2.0 180 Ringing Via: SIP/2.0/TCP 172.31.9.1:5060;branch=z9hG4bK3608975509 From: <sip:[EMAIL PROTECTED]>;tag=2216986771 To: <sip:[EMAIL PROTECTED]> Call-ID: [EMAIL PROTECTED] CSeq: 1 INVITE Accept: application/sdp Allow: INVITE, ACK, CANCEL, BYE Contact: <sip:[EMAIL PROTECTED]> Content-Length: 0 SIP/2.0 200 OK Via: SIP/2.0/TCP 172.31.9.1:5060;branch=z9hG4bK3608975509 From: <sip:[EMAIL PROTECTED]>;tag=2216986771 To: <sip:[EMAIL PROTECTED]>;tag=1613569299 Call-ID: [EMAIL PROTECTED] CSeq: 1 INVITE Accept: application/sdp Allow: INVITE, ACK, CANCEL, BYE Contact: <sip:[EMAIL PROTECTED]> Content-Type: application/sdp Content-Length: 191 v=0 o=root 1064518837 1064518837 IN IP4 172.31.9.1 s=Call from 172.31.9.1 c=IN IP4 172.31.9.1 t=0 0 m=audio 10186 RTP/AVP 8 101 a=rtpmap:8 pcma/8000 a=rtpmap:101 telephone-event/8000> ACK sip:[EMAIL PROTECTED] SIP/2.0 Via: SIP/2.0/TCP 172.31.9.165:5060;branch=z9hG4bK2002871224 <== This line indicates UDP From: <sip:[EMAIL PROTECTED]>;tag=2216986771 To: <sip:[EMAIL PROTECTED]>;tag=1613569299 Call-ID: [EMAIL PROTECTED] CSeq: 1 ACK Max-Forwards: 1 Content-Length: 0 < Datei: ATT00164.txt >>
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