新版SDP协议RFC4566

Network Working Group M. Handley Request for Comments: 4566 UCL Obsoletes: 2327, 3266 V. Jacobson Category: Standards Track Packet Design C. Perkins University of Glasgow July 2006 SDP: Session Description Protocol Status of This Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This memo defines the Session Description Protocol (SDP). SDP is intended for describing multimedia sessions for the purposes of session announcement, session invitation, and other forms of multimedia session initiation. Table of Contents 1. Introduction ....................................................3 2. Glossary of Terms ...............................................3 3. Examples of SDP Usage ...........................................4 3.1. Session Initiation .........................................4 3.2. Streaming Media ............................................4 3.3. Email and the World Wide Web ...............................4 3.4. Multicast Session Announcement .............................4 4. Requirements and Recommendations ................................5 4.1. Media and Transport Information ............................6 4.2. Timing Information .........................................6 4.3. Private Sessions ...........................................7 4.4. Obtaining Further Information about a Session ..............7 4.5. Categorisation .............................................7 4.6. Internationalisation .......................................7 Handley, et al. Standards Track [Page 1]  RFC 4566 SDP July 2006 5. SDP Specification ...............................................7 5.1. Protocol Version ("v=") ...................................10 5.2. Origin ("o=") .............................................11 5.3. Session Name ("s=") .......................................12 5.4. Session Information ("i=") ................................12 5.5. URI ("u=") ................................................13 5.6. Email Address and Phone Number ("e=" and "p=") ............13 5.7. Connection Data ("c=") ....................................14 5.8. Bandwidth ("b=") ..........................................16 5.9. Timing ("t=") .............................................17 5.10. Repeat Times ("r=") ......................................18 5.11. Time Zones ("z=") ........................................19 5.12. Encryption Keys ("k=") ...................................19 5.13. Attributes ("a=") ........................................21 5.14. Media Descriptions ("m=") ................................22 6. SDP Attributes .................................................24 7. Security Considerations ........................................31 8. IANA Considerations ............................................33 8.1. The "application/sdp" Media Type ..........................33 8.2. Registration of Parameters ................................34 8.2.1. Media Types ("media") ..............................34 8.2.2. Transport Protocols ("proto") ......................34 8.2.3. Media Formats ("fmt") ..............................35 8.2.4. Attribute Names ("att-field") ......................36 8.2.5. Bandwidth Specifiers ("bwtype") ....................37 8.2.6. Network Types ("nettype") ..........................37 8.2.7. Address Types ("addrtype") .........................38 8.2.8. Registration Procedure .............................38 8.3. Encryption Key Access Methods .............................39 9. SDP Grammar ....................................................39 10. Summary of Changes from RFC 2327 ..............................44 11. Acknowledgements ..............................................45 12. References ....................................................45 12.1. Normative References .....................................45 12.2. Informative References ...................................46 Handley, et al. Standards Track [Page 2]  RFC 4566 SDP July 2006 1. Introduction When initiating multimedia teleconferences, voice-over-IP calls, streaming video, or other sessions, there is a requirement to convey media details, transport addresses, and other session description metadata to the participants. SDP provides a standard representation for such information, irrespective of how that information is transported. SDP is purely a format for session description -- it does not incorporate a transport protocol, and it is intended to use different transport protocols as appropriate, including the Session Announcement Protocol [14], Session Initiation Protocol [15], Real Time Streaming Protocol [16], electronic mail using the MIME extensions, and the Hypertext Transport Protocol. SDP is intended to be general purpose so that it can be used in a wide range of network environments and applications. However, it is not intended to support negotiation of session content or media encodings: this is viewed as outside the scope of session description. This memo obsoletes RFC 2327 [6] and RFC 3266 [10]. Section 10 outlines the changes introduced in this memo. 2. Glossary of Terms The following terms are used in this document and have specific meaning within the context of this document. Conference: A multimedia conference is a set of two or more communicating users along with the software they are using to communicate. Session: A multimedia session is a set of multimedia senders and receivers and the data streams flowing from senders to receivers. A multimedia conference is an example of a multimedia session. Session Description: A well-defined format for conveying sufficient information to discover and participate in a multimedia session. 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 RFC 2119 [3]. Handley, et al. Standards Track [Page 3]  RFC 4566 SDP July 2006 3. Examples of SDP Usage 3.1. Session Initiation The Session Initiation Protocol (SIP) [15] is an application-layer control protocol for creating, modifying, and terminating sessions such as Internet multimedia conferences, Internet telephone calls, and multimedia distribution. The SIP messages used to create sessions carry session descriptions that allow participants to agree on a set of compatible media types. These session descriptions are commonly formatted using SDP. When used with SIP, the offer/answer model [17] provides a limited framework for negotiation using SDP. 3.2. Streaming Media The Real