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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) Summary: 3 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force SIP WG 3 Internet Draft G. Camarillo 4 Ericsson 5 H. Schulzrinne 6 Columbia University 7 E. Burger 8 SnowShore Networks 9 draft-camarillo-mmusic-source-sink-01.txt 10 August 28, 2003 11 Expires: February 2004 13 The Source and Sink Attributes for the Session Description Protocol 15 STATUS OF THIS MEMO 17 This document is an Internet-Draft and is in full conformance with 18 all provisions of Section 10 of RFC2026. 20 Internet-Drafts are working documents of the Internet Engineering 21 Task Force (IETF), its areas, and its working groups. Note that 22 other groups may also distribute working documents as Internet- 23 Drafts. 25 Internet-Drafts are draft documents valid for a maximum of six months 26 and may be updated, replaced, or obsoleted by other documents at any 27 time. It is inappropriate to use Internet-Drafts as reference 28 material or to cite them other than as "work in progress". 30 The list of current Internet-Drafts can be accessed at 31 http://www.ietf.org/ietf/1id-abstracts.txt 33 To view the list Internet-Draft Shadow Directories, see 34 http://www.ietf.org/shadow.html. 36 Abstract 38 This document defines two media level SDP attributes, namely source 39 and sink. They are intended to be used to invoke services that 40 involve media manipulation, such as transcoding services. 42 Table of Contents 44 1 Introduction ........................................ 3 45 1.1 Terminology ......................................... 3 46 2 Applicability ....................................... 3 47 3 Syntax of Source and Sink ........................... 3 48 4 SDP Example ......................................... 4 49 5 Use of Source and Sink with SIP ..................... 4 50 6 IANA Considerations ................................. 5 51 7 Security Considerations ............................. 5 52 8 Acknowledgements .................................... 5 53 9 Authors' Addresses .................................. 5 54 10 Normative References ................................ 5 55 11 Informative References .............................. 6 57 1 Introduction 59 Servers performing media manipulations, such as transcoding or 60 mixing, take the contents of one or several media streams as input 61 and send their output over another media stream. A client requesting 62 this type of service from a server needs to identify which media 63 streams are to be used as input and which ones will be used to send 64 the output of the media manipulation process. This document defines 65 two SDP media level attributes, namely source and sink, that can be 66 used to explicitly convey this information in an SDP session 67 description. 69 1.1 Terminology 71 In this document, the key words "MUST", "MUST NOT", "REQUIRED", 72 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", 73 and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and 74 indicate requirement levels for compliant SIP implementations. 76 2 Applicability 78 A server that provides simple media manipulation services between a 79 single unidirectional input (recvonly) stream and a single 80 unidirectional output (sendonly) stream, such as a text-to-speech 81 server, does not need to specify source and sink attributes in the 82 SDP. However, a server that needs to correlate more than the simple 83 media manipulation service needs a mechanism to specify which media 84 descriptions refer to which directionality of the input streams. 86 Thus, servers that use SDP [2] to provide more complex services that 87 involve more media streams (like some of the ones described by [5]) 88 SHOULD make use of the source and sink attributes. 90 The source and sink attributes MUST NOT be used to perform media 91 alignment between SIP [3] user agents. The nth matching rules defined 92 by the offer/answer model [4] must be used regardless of the presence 93 or absence of the sink and source attributes. 95 3 Syntax of Source and Sink 97 We define the following media level SDP attributes: 99 source-attribute = "a=source:" identification-tag 100 sink-attribute = "a=sink:" identification-tag 101 identification-tag = token 103 An SDP session description that contains a media stream with a 104 particular identification tag in a source attribute MUST have the 105 same identification tag in, at least, one sink attribute. An SDP 106 session description that contains a media stream with a particular 107 identification tag in a sink attribute MUST have the same 108 identification tag in, at least, one source attribute. 110 If an entity receives a session description that breaks the rules 111 stated above, it MUST act as if it had received a malformed session 112 description. 114 4 SDP Example 116 The SDP session description below sent to a server indicates that 117 incoming audio from the first stream has to be sent over the second 118 audio stream and over the text stream. Incoming text has to be sent 119 over the first audio stream (but not over the second one). The exact 120 media manipulations to be applied are typically identified by the URI 121 that identifies the service (e.g., sip:texttospeech@domain.com). 123 m=audio 40000 RTP/AVP 0 124 c=IN IP4 B.domain.com 125 a=source:1 126 a=sink:2 127 m=audio 20000 RTP/AVP 0 128 c=IN IP4 A.domain.com 129 a=recvonly 130 a=sink:1 131 m=text 20002 RTP/AVP t140 132 c=IN IP4 A.domain.com 133 a=source:2 134 a=sink:1 136 5 Use of Source and Sink with SIP 138 A user agent that wishes to use the source and sink attributes adds 139 them to an offer. The answerer SHOULD copy the same source and sink 140 attributes in its answer for all the streams that were accepted 141 (i.e., their port number is different than zero). 143 An answerer that understand the source and sink attributes MUST NOT 144 add or remove any of them from a stream that was accepted. The 145 offerer knows whether the answerer understands these attributes 146 because the answer will contain source and sink attributes. If the 147 answerer does not understand them, the answer will not contain source 148 and sink attributes. 150 6 IANA Considerations 152 This document defines two media level SDP attributes: "source" and 153 "sink". They should be registered in SDP parameters registry. 155 http://www.iana.org/assignments/sdp-parameters 157 7 Security Considerations 159 An attacker adding, removing or modifying source or sink a= lines 160 could change the expected behavior from a media manipulation service. 161 It is thus STRONGLY RECOMMENDED that integrity protection be applied 162 to the SDP session descriptions. For session descriptions carried in 163 SIP [3], S/MIME is the natural choice to provide such end-to-end 164 integrity protection, as described in RFC 3261. Other applications 165 MAY use a different form of integrity protection. 167 8 Acknowledgements 169 Jeff Van Dyke provided useful comments on this document. 171 9 Authors' Addresses 173 Gonzalo Camarillo 174 Ericsson 175 Advanced Signalling Research Lab. 176 FIN-02420 Jorvas 177 Finland 178 electronic mail: Gonzalo.Camarillo@ericsson.com 180 Henning Schulzrinne 181 Dept. of Computer Science 182 Columbia University 183 1214 Amsterdam Avenue 184 New York, NY 10027 185 USA 186 electronic mail: schulzrinne@cs.columbia.edu 188 Eric W. Burger 189 SnowShore Networks, Inc. 190 Chelmsford, MA 191 USA 192 electronic mail: eburger@snowshore.com 194 10 Normative References 196 [1] S. Bradner, "Key words for use in RFCs to indicate requirement 197 levels," RFC 2119, Internet Engineering Task Force, Mar. 1997. 199 [2] M. Handley and V. Jacobson, "SDP: session description protocol," 200 RFC 2327, Internet Engineering Task Force, Apr. 1998. 202 [3] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. R. Johnston, J. 203 Peterson, R. Sparks, M. Handley, and E. Schooler, "SIP: session 204 initiation protocol," RFC 3261, Internet Engineering Task Force, June 205 2002. 207 [4] J. Rosenberg and H. Schulzrinne, "An offer/answer model with 208 session description protocol (SDP)," RFC 3264, Internet Engineering 209 Task Force, June 2002. 211 11 Informative References 213 [5] N. Charlton, M. Gasson, G. Gybels, M. Spanner, and A. van Wijk, 214 "User requirements for the session initiation protocol (SIP) in 215 support of deaf, hard of hearing and speech-impaired individuals," 216 RFC 3351, Internet Engineering Task Force, Aug. 2002. 218 The IETF takes no position regarding the validity or scope of any 219 intellectual property or other rights that might be claimed to 220 pertain to the implementation or use of the technology described in 221 this document or the extent to which any license under such rights 222 might or might not be available; neither does it represent that it 223 has made any effort to identify any such rights. Information on the 224 IETF's procedures with respect to rights in standards-track and 225 standards-related documentation can be found in BCP-11. 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