Network Working Group C. Holmberg Internet-Draft Ericsson Updates: 5761 (if approved) September 15, 2016 Intended status: Standards Track Expires: March 19, 2017 Updates to RFC 5761 draft-ietf-avtcore-5761-update-02.txt Abstract This document updates RFC 5761 by clarifying the SDP offer/answer negotiation of RTP and RTCP multiplexing. It makes it clear that an answerer can only include an "a=rtcp-mux" attribute in an SDP answer if the associated SDP offer contained the attribute. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. 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Holmberg Expires March 19, 2017 [Page 1] Internet-Draft Updates to RFC 5761 September 2016 This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Update to RFC 5761 . . . . . . . . . . . . . . . . . . . . . 3 3.1. Update to section 5.1.1 . . . . . . . . . . . . . . . . . 3 4. Security Considerations . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 7. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 5 8. Normative References . . . . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction RFC 5761 [RFC5761] specifies how to multiplex RTP data packets and RTP Control Protocol (RTCP) packets on a single UDP port, and how to negotiate usage of such multiplexing using the SDP offer/answer mechanism [RFC3264], using an "a=rtcp-mux" attribute. However, the text is unclear on whether an answerer is allowed to include the attribute in an answer even if the associated offer did not contain an attribute. This document updates RFC 5761 [RFC5761] by clarifying that an answerer can only include an "a=rtcp-mux" attribute in an answer if the associated offer contained the attribute. It also clarifies that the negotiation of RTP and RTCP multiplexing is for usage in both directions. 2. Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Holmberg Expires March 19, 2017 [Page 2] Internet-Draft Updates to RFC 5761 September 2016 3. Update to RFC 5761 This section updates section 5.1.1 of RFC 5761 by clarifying that an answerer can only include an "a=rtcp-mux" attribute in an answer if the associated offer contained the attribute, and by clarifying that the negotiation of RTP and RTCP multiplexing is for usage in both directions. 3.1. Update to section 5.1.1 OLD TEXT: When the Session Description Protocol (SDP) [8] is used to negotiate RTP sessions following the offer/answer model [9], the "a=rtcp-mux" attribute (see Section 8) indicates the desire to multiplex RTP and RTCP onto a single port. The initial SDP offer MUST include this attribute at the media level to request multiplexing of RTP and RTCP on a single port. For example: v=0 o=csp 1153134164 1153134164 IN IP6 2001:DB8::211:24ff:fea3:7a2e s=- c=IN IP6 2001:DB8::211:24ff:fea3:7a2e t=1153134164 1153137764 m=audio 49170 RTP/AVP 97 a=rtpmap:97 iLBC/8000 a=rtcp-mux This offer denotes a unicast voice-over-IP session using the RTP/AVP profile with iLBC coding. The answerer is requested to send both RTP and RTCP to port 49170 on IPv6 address 2001:DB8::211:24ff:fea3:7a2e. If the answerer wishes to multiplex RTP and RTCP onto a single port, it MUST include a media-level "a=rtcp-mux" attribute in the answer. The RTP payload types used in the answer MUST conform to the rules in Section 4. If the answer does not contain an "a=rtcp-mux" attribute, the offerer MUST NOT multiplex RTP and RTCP packets on a single port. Instead, it should send and receive RTCP on a port allocated according to the usual port-selection rules (either the port pair, or a signalled port if the "a=rtcp:" attribute [10] is also included). This will occur when talking to a peer that does not understand the "a=rtcp-mux" attribute. When SDP is used in a declarative manner, the presence of an "a=rtcp- mux" attribute signals that the sender will multiplex RTP and RTCP on Holmberg Expires March 19, 2017 [Page 3] Internet-Draft Updates to RFC 5761 September 2016 the same port. The receiver MUST be prepared to receive RTCP packets on the RTP port, and any resource reservation needs to be made including the RTCP bandwidth. NEW TEXT: When the Session Description Protocol (SDP) [8] is used to negotiate RTP sessions following the offer/answer model [9], the "a=rtcp-mux" attribute (see Section 8) indicates the desire to multiplex RTP and RTCP onto a single port, and the usage is always negotiated for both directions. If the offerer wishes to multiplex RTP and RTCP onto a single port, the initial SDP offer MUST include the attribute at the media level to request multiplexing of RTP and RTCP on a single port. For example: v=0 o=csp 1153134164 1153134164 IN IP6 2001:DB8::211:24ff:fea3:7a2e s=- c=IN IP6 2001:DB8::211:24ff:fea3:7a2e t=1153134164 1153137764 m=audio 49170 RTP/AVP 97 a=rtpmap:97 iLBC/8000 a=rtcp-mux This offer denotes a unicast voice-over-IP session using the RTP/AVP profile with iLBC coding. The answerer is requested to send both RTP and RTCP to port 49170 on IPv6 address 2001:DB8::211:24ff:fea3:7a2e. If the offer contains the "a=rtcp-mux" attribute, and if the answerer wishes to multiplex RTP and RTCP onto a single port, it MUST include a media-level "a=rtcp-mux" attribute in the answer. The RTP payload types used in the answer MUST conform to the rules in Section 4. If the offer does not contain the "a=rtcp-mux" attribute the answerer MUST NOT include an "a=rtcp-mux" attribute in the answer, and the answerer MUST NOT multiplex RTP and RTCP packets on a single port. If the answerer includes an "a=rtcp-mux" attribute in the answer, the offerer and answerer MUST multiplex RTP and RTCP packets on a single port. If the answer does not contain an "a=rtcp-mux" attribute, the offerer and answerer MUST NOT multiplex RTP and RTCP packets on a single port. Instead, they should send and receive RTCP on a port allocated according to the usual port-selection rules (either the port pair, or a signalled port if the "a=rtcp:" attribute [10] is also included). This will occur when talking to a peer that does not understand the Holmberg Expires March 19, 2017 [Page 4] Internet-Draft Updates to RFC 5761 September 2016 "a=rtcp-mux" attribute. When SDP is used in a declarative manner, the presence of an "a=rtcp- mux" attribute signals that the sender will multiplex RTP and RTCP on the same port. The receiver MUST be prepared to receive RTCP packets on the RTP port, and any resource reservation needs to be made including the RTCP bandwidth. 4. Security Considerations The security considerations for RTP and RTCP multiplexing are described in RFC 5761. This specification does not impact those security considerations. 5. IANA Considerations This specifcation makes no requests from IANA. 6. Acknowledgements Thanks to Colin Perkins, Magnus Westerlund, Paul Kyzivat, Roni Even for providing comments on the document. Thomas Belling provided useful input in the discussions that took place in 3GPP and resulated in the submission of the document. 7. Change Log [RFC EDITOR NOTE: Please remove this section when publishing] Change from -01 o pre-RFC5378 disclaimer added. Change from -00 o Editorial changes based on WGLC comments from Roni Even. 8. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Holmberg Expires March 19, 2017 [Page 5] Internet-Draft Updates to RFC 5761 September 2016 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, DOI 10.17487/RFC3264, June 2002, . [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and Control Packets on a Single Port", RFC 5761, DOI 10.17487/RFC5761, April 2010, . Author's Address Christer Holmberg Ericsson Hirsalantie 11 Jorvas 02420 Finland Email: christer.holmberg@ericsson.com Holmberg Expires March 19, 2017 [Page 6]