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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 2327 (ref. '2') (Obsoleted by RFC 4566) ** Obsolete normative reference: RFC 3388 (ref. '4') (Obsoleted by RFC 5888) == Outdated reference: A later version (-04) exists of draft-ietf-xcon-cpcp-reqs-03 Summary: 8 errors (**), 0 flaws (~~), 6 warnings (==), 8 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 MMUSIC O. Levin 2 Internet-Draft Microsoft Corporation 3 Expires: December 28, 2004 G. Camarillo 4 Ericsson 5 June 29, 2004 7 The SDP (Session Description Protocol) Label Attribute 8 draft-levin-mmusic-sdp-media-label-00 10 Status of this Memo 12 By submitting this Internet-Draft, I certify that any applicable 13 patent or other IPR claims of which I am aware have been disclosed, 14 and any of which I become aware will be disclosed, in accordance with 15 RFC 3668. 17 Internet-Drafts are working documents of the Internet Engineering 18 Task Force (IETF), its areas, and its working groups. Note that 19 other groups may also distribute working documents as 20 Internet-Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/ietf/1id-abstracts.txt. 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html. 33 This Internet-Draft will expire on December 28, 2004. 35 Copyright Notice 37 Copyright (C) The Internet Society (2004). All Rights Reserved. 39 Abstract 41 This document defines a new Session Description Protocol (SDP) 42 media-level attribute: "label". The "label" attribute carries a 43 pointer to an application layer media stream identifier in the 44 context of an arbitrary network application that uses SDP. The 45 sender of the SDP document can attach the "label" attribute to a 46 particular media stream or media streams. The application receiving 47 the SDP document can then associate the particular media stream with 48 its application semantics or role. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 53 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 3. The Label Attribute . . . . . . . . . . . . . . . . . . . . . 4 55 4. The Label Attribute in the Offer/Answer Model . . . . . . . . 4 56 5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 57 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 58 7. Security Considerations . . . . . . . . . . . . . . . . . . . 5 59 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 60 8.1 Normative References . . . . . . . . . . . . . . . . . . . . 5 61 8.2 Informative References . . . . . . . . . . . . . . . . . . . 6 62 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 6 63 Intellectual Property and Copyright Statements . . . . . . . . 7 65 1. Introduction 67 SDP is being used by a variety of distributed over the network 68 applications. These applications deal with multiple SDP sessions 69 serving multiple users or services in the context of a single 70 application instance. As such, applications of this kind have their 71 means to identify a particular media stream across multiple SDP 72 sessions. 74 XCON framework [6] is an example of a centralized conference 75 architecture that uses SDP according to the Offer/Answer mechanism 76 defined in [3] to establish media streams with each of the conference 77 participants. Additionally, XCON defines the means to uniquely 78 identify a media stream in terms of its role in a conference 79 regardless its media type, transport protocol, and media format. It 80 is necessary to convey a pointer to this application layer identifier 81 in SDP. As a result, the application can choose from the media 82 streams offered in the SDP based not only on their media 83 characteristics, but also according to their roles in the 84 application. 86 This specification defines the SDP [2] "label" media-level attribute, 87 which carries the pointer to the application layer media stream 88 identifier in the SDP document across the network. 90 Note that the "i" SDP attribute, defined in RFC 2327 [2], can be used 91 to label media streams as well. Nevertheless, the audiences for the 92 "i" and the "label" attributes are different. While "i" values are 93 presented to the users as is, "label" values are processed by 94 automata. 96 Note that the "mid" SDP attribute, defined in RFC 3388 [4], can be 97 used to identify media streams as well. Nevertheless, the scopes of 98 the "mid" and the "label" attributes are different. While "mid" 99 values are meaningful in the context of a single SDP session, "label" 100 values are meaningful in the context of an application (e.g., a 101 multiparty application). 103 2. Terminology 105 In this document, the key words "MUST", "MUST NOT", "REQUIRED", 106 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT 107 RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as 108 described in BCP 14, RFC 2119 [1] and indicate requirement levels for 109 compliant implementations. 111 3. The Label Attribute 113 This specification defines a new media-level value attribute: 114 "label". Its formatting in SDP is described by the following BNF: 116 label-attribute = "a=label:" pointer 117 pointer = token 119 The semantics of the "label" attribute MUST be defined by 120 applications that use SDP with "label". This value is the 121 application layer identifier for a media stream regardless of its 122 media type, transport protocol, or media format. 124 4. The Label Attribute in the Offer/Answer Model 126 This specification does not define means to discover whether or not 127 the remote endpoint understands the "label" attribute. We have 128 chosen not to provide such a mechanism within this specification 129 because "label" values are only informative at the Offer/Answer model 130 level. 132 To the Offer/Answer mechanism, it means that the fact that an offer 133 does not contain label attributes does not imply that the answer 134 should not have them. It also means that the fact that an offer 135 contains label attributes does not imply that the answer should have 136 them too. 138 In addition to the basic Offer/Answer rule above, applications that 139 use "label" as a pointer to media streams MUST define both the 140 "label" application semantics and its usage constraints. For 141 example, the specifications of such applications MAY mandate support 142 for "label". In this case, the application MUST define means for 143 negotiation of the "label" attribute support as a part of the 144 application. 146 5. Example 148 The following is an example of an SDP session description that uses 149 the "label" attribute: 151 v=0 152 o=bob 280744730 28977631 IN IP4 host.example.com 153 s= 154 c=IN IP4 192.0.2.2 155 t=0 0 156 m=audio 6886 RTP/AVP 0 157 a=label:1 158 m=audio 22334 RTP/AVP 0 159 a=label:2 161 6. IANA Considerations 163 Contact name: Orit Levin oritl@microsoft.com. 165 Attribute name: "label". 167 Type of attribute Media level. 169 Subject to charset: Not. 171 Purpose of attribute: "Label" attribute associates the media stream 172 with specific application semantics. During the SDP Offer-Answer 173 mechanism, it allows application to make smarter choices 174 especially among m-lines of the same media type. In a context of 175 a multiparty application, it allows the application to pick out an 176 offered media stream based on its role in the application as the 177 only available meaningful identifier beyond a single SDP session 178 (i.e., across the application participants). 180 Allowed attribute values: Any octet string. 182 7. Security Considerations 184 An attacker may attempt to add, modify, or remove "label" attributes 185 from a session description. This could result in an application 186 behaving in a non-desirable way. So, it is STRONGLY RECOMMENDED that 187 integrity protection be applied to the SDP session descriptions. For 188 session descriptions carried in SIP [5], S/MIME is the natural choice 189 to provide such end-to-end integrity protection, as described in RFC 190 3261 [5]. Other applications MAY use a different form of integrity 191 protection. 193 8. References 195 8.1 Normative References 197 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 198 Levels", BCP 14, RFC 2119, March 1997. 200 [2] Handley, M. and V. Jacobson, "SDP: Session Description 201 Protocol", RFC 2327, April 1998. 203 [3] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with 204 Session Description Protocol (SDP)", RFC 3264, June 2002. 206 [4] Camarillo, G., Eriksson, G., Holler, J. and H. Schulzrinne, 207 "Grouping of Media Lines in the Session Description Protocol 208 (SDP)", RFC 3388, December 2002. 210 8.2 Informative References 212 [5] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., 213 Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: 214 Session Initiation Protocol", RFC 3261, June 2002. 216 [6] Koskelainen, P. and H. Khartabil, "Requirements for Conference 217 Policy Control Protocol", draft-ietf-xcon-cpcp-reqs-03 (work in 218 progress), April 2004. 220 Authors' Addresses 222 Orit Levin 223 Microsoft Corporation 224 One Microsoft Way 225 Redmond, WA 98052 226 USA 228 EMail: oritl@microsoft.com 230 Gonzalo Camarillo 231 Ericsson 232 Hirsalantie 11 233 Jorvas 02420 234 Finland 236 EMail: Gonzalo.Camarillo@ericsson.com 238 Intellectual Property Statement 240 The IETF takes no position regarding the validity or scope of any 241 Intellectual Property Rights or other rights that might be claimed to 242 pertain to the implementation or use of the technology described in 243 this document or the extent to which any license under such rights 244 might or might not be available; nor does it represent that it has 245 made any independent effort to identify any such rights. 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Please address the information to the IETF at 260 ietf-ipr@ietf.org. 262 Disclaimer of Validity 264 This document and the information contained herein are provided on an 265 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 266 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 267 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 268 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 269 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 270 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 272 Copyright Statement 274 Copyright (C) The Internet Society (2004). This document is subject 275 to the rights, licenses and restrictions contained in BCP 78, and 276 except as set forth therein, the authors retain all their rights. 278 Acknowledgment 280 Funding for the RFC Editor function is currently provided by the 281 Internet Society.