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Holmberg 3 Internet-Draft Ericsson 4 Updates: 5761 (if approved) August 10, 2016 5 Intended status: Standards Track 6 Expires: February 11, 2017 8 Updates to RFC 5761 9 draft-ietf-avtcore-5761-update-01.txt 11 Abstract 13 This document updates RFC 5761 by clarifying the SDP offer/answer 14 negotiation of RTP and RTCP multiplexing. It makes it clear that an 15 answerer can only include an "a=rtcp-mux" attribute in an SDP answer 16 if the associated SDP offer contained the attribute. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on February 11, 2017. 35 Copyright Notice 37 Copyright (c) 2016 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 53 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 2 54 3. Update to RFC 5761 . . . . . . . . . . . . . . . . . . . . . 2 55 3.1. Update to the sixth paragraph of section 5 . . . . . . . 2 56 4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 57 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 58 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 59 7. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 5 60 8. Normative References . . . . . . . . . . . . . . . . . . . . 5 61 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 63 1. Introduction 65 RFC 5761 [RFC5761] specifies how to multiplex RTP data packets and 66 RTP Control Protocol (RTCP) packets on a single UDP port, and how to 67 negotiate usage of such multiplexing using the SDP offer/answer 68 mechanism [RFC3264], using an "a=rtcp-mux" attribute. However, the 69 text is unclear on whether an answerer is allowed to include the 70 attribute in an answer even if the associated offer did not contain 71 an attribute. 73 This document updates RFC 5761 [RFC5761] by clarifying that an 74 answerer can only include an "a=rtcp-mux" attribute in an answer if 75 the associated offer contained the attribute. It also clarifies that 76 the negotiation of RTP and RTCP multiplexing is for usage in both 77 directions. 79 2. Conventions 81 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 82 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 83 document are to be interpreted as described in [RFC2119]. 85 3. Update to RFC 5761 87 This section updates section 5.1.1 of RFC 5761. 89 3.1. Update to the sixth paragraph of section 5 91 OLD TEXT: 93 When the Session Description Protocol (SDP) [8] is used to negotiate 94 RTP sessions following the offer/answer model [9], the "a=rtcp-mux" 95 attribute (see Section 8) indicates the desire to multiplex RTP and 96 RTCP onto a single port. The initial SDP offer MUST include this 97 attribute at the media level to request multiplexing of RTP and RTCP 98 on a single port. For example: 100 v=0 101 o=csp 1153134164 1153134164 IN IP6 2001:DB8::211:24ff:fea3:7a2e 102 s=- 103 c=IN IP6 2001:DB8::211:24ff:fea3:7a2e 104 t=1153134164 1153137764 105 m=audio 49170 RTP/AVP 97 106 a=rtpmap:97 iLBC/8000 107 a=rtcp-mux 109 This offer denotes a unicast voice-over-IP session using the RTP/AVP 110 profile with iLBC coding. The answerer is requested to send both RTP 111 and RTCP to port 49170 on IPv6 address 2001:DB8::211:24ff:fea3:7a2e. 113 If the answerer wishes to multiplex RTP and RTCP onto a single port, 114 it MUST include a media-level "a=rtcp-mux" attribute in the answer. 115 The RTP payload types used in the answer MUST conform to the rules in 116 Section 4. 118 If the answer does not contain an "a=rtcp-mux" attribute, the offerer 119 MUST NOT multiplex RTP and RTCP packets on a single port. Instead, 120 it should send and receive RTCP on a port allocated according to the 121 usual port-selection rules (either the port pair, or a signalled port 122 if the "a=rtcp:" attribute [10] is also included). This will occur 123 when talking to a peer that does not understand the "a=rtcp-mux" 124 attribute. 126 When SDP is used in a declarative manner, the presence of an "a=rtcp- 127 mux" attribute signals that the sender will multiplex RTP and RTCP on 128 the same port. The receiver MUST be prepared to receive RTCP packets 129 on the RTP port, and any resource reservation needs to be made 130 including the RTCP bandwidth. 132 NEW TEXT: 134 When the Session Description Protocol (SDP) [8] is used to negotiate 135 RTP sessions following the offer/answer model [9], the "a=rtcp-mux" 136 attribute (see Section 8) indicates the desire to multiplex RTP and 137 RTCP onto a single port, and the usage is always negotiated for both 138 directions. 140 If the offerer wishes to multiplex RTP and RTCP onto a single port, 141 the initial SDP offer MUST include the attribute at the media level to 142 request multiplexing of RTP and RTCP on a single port. For example: 144 v=0 145 o=csp 1153134164 1153134164 IN IP6 2001:DB8::211:24ff:fea3:7a2e 146 s=- 147 c=IN IP6 2001:DB8::211:24ff:fea3:7a2e 148 t=1153134164 1153137764 149 m=audio 49170 RTP/AVP 97 150 a=rtpmap:97 iLBC/8000 151 a=rtcp-mux 153 This offer denotes a unicast voice-over-IP session using the RTP/AVP 154 profile with iLBC coding. The answerer is requested to send both RTP 155 and RTCP to port 49170 on IPv6 address 2001:DB8::211:24ff:fea3:7a2e. 157 If the offer contains the "a=rtcp-mux" attribute, and if the answerer 158 wishes to multiplex RTP and RTCP onto a single port, it MUST include a 159 media-level "a=rtcp-mux" attribute in the answer. The RTP payload 160 types used in the answer MUST conform to the rules in Section 4. If 161 the offer does not contain the "a=rtcp-mux" attribute the answerer 162 MUST NOT include an "a=rtcp-mux" attribute in the answer, and the 163 answerer MUST NOT multiplex RTP and RTCP packets on a single port. 165 If the answerer includes an "a=rtcp-mux" attribute in the answer, the 166 offerer and answerer MUST multiplex RTP and RTCP packets on a single 167 port. 169 If the answer does not contain an "a=rtcp-mux" attribute, the offerer 170 and answerer MUST NOT multiplex RTP and RTCP packets on a single port. 171 Instead, they should send and receive RTCP on a port allocated 172 according to the usual port-selection rules (either the port pair, or 173 a signalled port if the "a=rtcp:" attribute [10] is also included). 174 This will occur when talking to a peer that does not understand the 175 "a=rtcp-mux" attribute. 177 When SDP is used in a declarative manner, the presence of an "a=rtcp- 178 mux" attribute signals that the sender will multiplex RTP and RTCP on 179 the same port. The receiver MUST be prepared to receive RTCP packets 180 on the RTP port, and any resource reservation needs to be made 181 including the RTCP bandwidth. 183 4. Security Considerations 185 The security considerations for RTP and RTCP multiplexing are 186 described in RFC 5761. This specification does not impact those 187 security considerations. 189 5. IANA Considerations 191 This specifcation makes no requests from IANA. 193 6. Acknowledgements 195 Thanks to Colin Perkins, Magnus Westerlund, Paul Kyzivat, Roni Even 196 for providing comments on the document. Thomas Belling provided 197 useful input in the discussions that took place in 3GPP and resulated 198 in the submission of the document. 200 7. Change Log 202 [RFC EDITOR NOTE: Please remove this section when publishing] 204 Change from -00 206 o Editorial changes based on WGLC comments from Roni Even. 208 8. Normative References 210 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 211 Requirement Levels", BCP 14, RFC 2119, 212 DOI 10.17487/RFC2119, March 1997, 213 . 215 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 216 with Session Description Protocol (SDP)", RFC 3264, 217 DOI 10.17487/RFC3264, June 2002, 218 . 220 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 221 Control Packets on a Single Port", RFC 5761, 222 DOI 10.17487/RFC5761, April 2010, 223 . 225 Author's Address 227 Christer Holmberg 228 Ericsson 229 Hirsalantie 11 230 Jorvas 02420 231 Finland 233 Email: christer.holmberg@ericsson.com