idnits 2.17.1 draft-ietf-mmusic-rfc4566bis-18.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** There are 3 instances of too long lines in the document, the longest one being 30 characters in excess of 72. == There are 1 instance of lines with multicast IPv4 addresses in the document. If these are generic example addresses, they should be changed to use the 233.252.0.x range defined in RFC 5771 Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document seems to contain a disclaimer for pre-RFC5378 work, and may have content which was first submitted before 10 November 2008. The disclaimer is necessary when there are original authors that you have been unable to contact, or if some do not wish to grant the BCP78 rights to the IETF Trust. If you are able to get all authors (current and original) to grant those rights, you can and should remove the disclaimer; otherwise, the disclaimer is needed and you can ignore this comment. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (February 4, 2017) is 2628 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFC2848' is mentioned on line 2222, but not defined == Missing Reference: 'RFC3108' is mentioned on line 2227, but not defined == Missing Reference: 'RFC7195' is mentioned on line 2228, but not defined == Missing Reference: 'RFC4145' is mentioned on line 2256, but not defined == Missing Reference: 'RFC6135' is mentioned on line 2256, but not defined == Missing Reference: 'I-D.mmusic-msrp-usage-data-channel' is mentioned on line 2257, but not defined == Unused Reference: 'I-D.iana-charset-reg-procedure' is defined on line 2605, but no explicit reference was found in the text ** Obsolete normative reference: RFC 5226 (Obsoleted by RFC 8126) ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) ** Downref: Normative reference to an Informational RFC: RFC 7656 == Outdated reference: A later version (-19) exists of draft-ietf-mmusic-sdp-mux-attributes-16 == Outdated reference: A later version (-28) exists of draft-ietf-mmusic-data-channel-sdpneg-11 -- Obsolete informational reference (is this intentional?): RFC 2327 (Obsoleted by RFC 4566) -- Obsolete informational reference (is this intentional?): RFC 2326 (Obsoleted by RFC 7826) -- Obsolete informational reference (is this intentional?): RFC 5245 (Obsoleted by RFC 8445, RFC 8839) Summary: 4 errors (**), 0 flaws (~~), 11 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group M. Handley 3 Internet-Draft UCL 4 Obsoletes: 4566 (if approved) V. Jacobson 5 Intended status: Standards Track PARC 6 Expires: August 8, 2017 C. Perkins 7 University of Glasgow 8 A. Begen 9 Networked Media 10 February 4, 2017 12 SDP: Session Description Protocol 13 draft-ietf-mmusic-rfc4566bis-18 15 Abstract 17 This memo defines the Session Description Protocol (SDP). SDP is 18 intended for describing multimedia sessions for the purposes of 19 session announcement, session invitation, and other forms of 20 multimedia session initiation. This document obsoletes RFC 4566. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on August 8, 2017. 39 Copyright Notice 41 Copyright (c) 2017 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 This document may contain material from IETF Documents or IETF 55 Contributions published or made publicly available before November 56 10, 2008. The person(s) controlling the copyright in some of this 57 material may not have granted the IETF Trust the right to allow 58 modifications of such material outside the IETF Standards Process. 59 Without obtaining an adequate license from the person(s) controlling 60 the copyright in such materials, this document may not be modified 61 outside the IETF Standards Process, and derivative works of it may 62 not be created outside the IETF Standards Process, except to format 63 it for publication as an RFC or to translate it into languages other 64 than English. 66 Table of Contents 68 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 69 2. Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . 4 70 3. Examples of SDP Usage . . . . . . . . . . . . . . . . . . . . 4 71 3.1. Session Initiation . . . . . . . . . . . . . . . . . . . 4 72 3.2. Streaming Media . . . . . . . . . . . . . . . . . . . . . 5 73 3.3. Email and the World Wide Web . . . . . . . . . . . . . . 5 74 3.4. Multicast Session Announcement . . . . . . . . . . . . . 5 75 4. Requirements and Recommendations . . . . . . . . . . . . . . 5 76 4.1. Media and Transport Information . . . . . . . . . . . . . 6 77 4.2. Timing Information . . . . . . . . . . . . . . . . . . . 7 78 4.3. Obtaining Further Information about a Session . . . . . . 7 79 4.4. Categorisation . . . . . . . . . . . . . . . . . . . . . 8 80 4.5. Internationalisation . . . . . . . . . . . . . . . . . . 8 81 5. SDP Specification . . . . . . . . . . . . . . . . . . . . . . 8 82 5.1. Protocol Version ("v=") . . . . . . . . . . . . . . . . . 11 83 5.2. Origin ("o=") . . . . . . . . . . . . . . . . . . . . . . 12 84 5.3. Session Name ("s=") . . . . . . . . . . . . . . . . . . . 13 85 5.4. Session Information ("i=") . . . . . . . . . . . . . . . 13 86 5.5. URI ("u=") . . . . . . . . . . . . . . . . . . . . . . . 14 87 5.6. Email Address and Phone Number ("e=" and "p=") . . . . . 14 88 5.7. Connection Data ("c=") . . . . . . . . . . . . . . . . . 15 89 5.8. Bandwidth ("b=") . . . . . . . . . . . . . . . . . . . . 17 90 5.9. Timing ("t=") . . . . . . . . . . . . . . . . . . . . . . 18 91 5.10. Repeat Times ("r=") . . . . . . . . . . . . . . . . . . . 19 92 5.11. Time Zones ("z=") . . . . . . . . . . . . . . . . . . . . 19 93 5.12. Encryption Keys ("k=") . . . . . . . . . . . . . . . . . 20 94 5.13. Attributes ("a=") . . . . . . . . . . . . . . . . . . . . 22 95 5.14. Media Descriptions ("m=") . . . . . . . . . . . . . . . . 23 96 6. SDP Attributes . . . . . . . . . . . . . . . . . . . . . . . 25 97 6.1. cat (category) . . . . . . . . . . . . . . . . . . . . . 26 98 6.2. keywds (keywords) . . . . . . . . . . . . . . . . . . . . 26 99 6.3. tool . . . . . . . . . . . . . . . . . . . . . . . . . . 27 100 6.4. ptime (packet time) . . . . . . . . . . . . . . . . . . . 27 101 6.5. maxptime (maximum packet time) . . . . . . . . . . . . . 28 102 6.6. rtpmap . . . . . . . . . . . . . . . . . . . . . . . . . 28 103 6.7. Media Direction Attributes . . . . . . . . . . . . . . . 30 104 6.7.1. recvonly (receive-only) . . . . . . . . . . . . . . . 31 105 6.7.2. sendrecv (send-receive) . . . . . . . . . . . . . . . 31 106 6.7.3. sendonly (send-only) . . . . . . . . . . . . . . . . 32 107 6.7.4. inactive . . . . . . . . . . . . . . . . . . . . . . 32 108 6.8. orient (orientation) . . . . . . . . . . . . . . . . . . 33 109 6.9. type (conference type) . . . . . . . . . . . . . . . . . 33 110 6.10. charset (character set) . . . . . . . . . . . . . . . . . 34 111 6.11. sdplang (SDP language) . . . . . . . . . . . . . . . . . 35 112 6.12. lang (language) . . . . . . . . . . . . . . . . . . . . . 36 113 6.13. framerate (frame rate) . . . . . . . . . . . . . . . . . 37 114 6.14. quality . . . . . . . . . . . . . . . . . . . . . . . . . 38 115 6.15. fmtp (format parameters) . . . . . . . . . . . . . . . . 38 116 7. Security Considerations . . . . . . . . . . . . . . . . . . . 39 117 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 41 118 8.1. The "application/sdp" Media Type . . . . . . . . . . . . 41 119 8.2. Registration of Parameters . . . . . . . . . . . . . . . 43 120 8.2.1. Media Types ("media") . . . . . . . . . . . . . . . . 43 121 8.2.2. Transport Protocols ("proto") . . . . . . . . . . . . 43 122 8.2.3. Media Formats ("fmt") . . . . . . . . . . . . . . . . 44 123 8.2.4. Attribute Names ("att-field") . . . . . . . . . . . . 44 124 8.2.5. Bandwidth Specifiers ("bwtype") . . . . . . . . . . . 47 125 8.2.6. Network Types ("nettype") . . . . . . . . . . . . . . 47 126 8.2.7. Address Types ("addrtype") . . . . . . . . . . . . . 48 127 8.2.8. Registration Procedure . . . . . . . . . . . . . . . 48 128 8.3. Encryption Key Access Methods . . . . . . . . . . . . . . 49 129 8.4. Reorganization of the nettype Registry . . . . . . . . . 49 130 8.5. Reorganization of the att-field Registries . . . . . . . 49 131 9. SDP Grammar . . . . . . . . . . . . . . . . . . . . . . . . . 50 132 10. Summary of Changes from RFC 4566 . . . . . . . . . . . . . . 55 133 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 56 134 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 56 135 12.1. Normative References . . . . . . . . . . . . . . . . . . 56 136 12.2. Informative References . . . . . . . . . . . . . . . . . 57 137 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 60 139 1. Introduction 141 When initiating multimedia teleconferences, voice-over-IP calls, 142 streaming video, or other sessions, there is a requirement to convey 143 media details, transport addresses, and other session description 144 metadata to the participants. 146 SDP provides a standard representation for such information, 147 irrespective of how that information is transported. SDP is purely a 148 format for session description -- it does not incorporate a transport 149 protocol, and it is intended to use different transport protocols as 150 appropriate, including the Session Announcement Protocol (SAP) 151 [RFC2974], Session Initiation Protocol (SIP) [RFC3261], Real Time 152 Streaming Protocol (RTSP) [RFC2326], electronic mail using the MIME 153 extensions, and the Hypertext Transport Protocol (HTTP). 155 SDP is intended to be general purpose so that it can be used in a 156 wide range of network environments and applications. However, it is 157 not intended to support negotiation of session content or media 158 encodings: this is viewed as outside the scope of session 159 description. 161 This memo obsoletes [RFC4566]. The changes relative to [RFC4566] are 162 limited to essential corrections, and are outlined in Section 10 of 163 this memo. 165 2. Glossary of Terms 167 The following term is used in this document and has specific meaning 168 within the context of this document. 170 Session Description: A well-defined format for conveying sufficient 171 information to discover and participate in a multimedia session. 173 The terms "multimedia conference" and "multimedia session" are used 174 in this document as defined in [RFC7656]. The terms "session" and 175 "multimedia session" are used interchangeably in this document. 177 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 178 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 179 "OPTIONAL" in this document are to be interpreted as described in 180 [RFC2119]. 182 3. Examples of SDP Usage 184 3.1. Session Initiation 186 The Session Initiation Protocol (SIP) [RFC3261] is an application- 187 layer control protocol for creating, modifying, and terminating 188 sessions such as Internet multimedia conferences, Internet telephone 189 calls, and multimedia distribution. The SIP messages used to create 190 sessions carry session descriptions that allow participants to agree 191 on a set of compatible media types. These session descriptions are 192 commonly formatted using SDP. When used with SIP, the offer/answer 193 model [RFC3264] provides a limited framework for negotiation using 194 SDP. 196 3.2. Streaming Media 198 The Real Time Streaming Protocol (RTSP) [RFC2326], is an application- 199 level protocol for control over the delivery of data with real-time 200 properties. RTSP provides an extensible framework to enable 201 controlled, on-demand delivery of real-time data, such as audio and 202 video. An RTSP client and server negotiate an appropriate set of 203 parameters for media delivery, partially using SDP syntax to describe 204 those parameters. 206 3.3. Email and the World Wide Web 208 Alternative means of conveying session descriptions include 209 electronic mail and the World Wide Web (WWW). For both email and WWW 210 distribution, the media type "application/sdp" is used. This enables 211 the automatic launching of applications for participation in the 212 session from the WWW client or mail reader in a standard manner. 214 Note that announcements of multicast sessions made only via email or 215 the WWW do not have the property that the receiver of a session 216 announcement can necessarily receive the session because the 217 multicast sessions may be restricted in scope, and access to the WWW 218 server or reception of email is possible outside this scope. 220 3.4. Multicast Session Announcement 222 In order to assist the advertisement of multicast multimedia 223 conferences and other multicast sessions, and to communicate the 224 relevant session setup information to prospective participants, a 225 distributed session directory may be used. An instance of such a 226 session directory periodically sends packets containing a description 227 of the session to a well-known multicast group. These advertisements 228 are received by other session directories such that potential remote 229 participants can use the session description to start the tools 230 required to participate in the session. 232 One protocol used to implement such a distributed directory is the 233 SAP [RFC2974]. SDP provides the recommended session description 234 format for such session announcements. 236 4. Requirements and Recommendations 238 The purpose of SDP is to convey information about media streams in 239 multimedia sessions to allow the recipients of a session description 240 to participate in the session. SDP is primarily intended for use in 241 an internetwork, although it is sufficiently general that it can 242 describe multimedia conferences in other network environments. Media 243 streams can be many-to-many. Sessions need not be continually 244 active. 246 Thus far, multicast-based sessions on the Internet have differed from 247 many other forms of conferencing in that anyone receiving the traffic 248 can join the session (unless the session traffic is encrypted). In 249 such an environment, SDP serves two primary purposes. It is a means 250 to communicate the existence of a session, and it is a means to 251 convey sufficient information to enable joining and participating in 252 the session. In a unicast environment, only the latter purpose is 253 likely to be relevant. 255 An SDP description includes the following: 257 o Session name and purpose 259 o Time(s) the session is active 261 o The media comprising the session 263 o Information needed to receive those media (addresses, ports, 264 formats, etc.) 266 As resources necessary to participate in a session may be limited, 267 some additional information may also be desirable: 269 o Information about the bandwidth to be used by the session 271 o Contact information for the person responsible for the session 273 In general, SDP must convey sufficient information to enable 274 applications to join a session (with the possible exception of 275 encryption keys) and to announce the resources to be used to any non- 276 participants that may need to know. (This latter feature is 277 primarily useful when SDP is used with a multicast session 278 announcement protocol.) 280 4.1. Media and Transport Information 282 An SDP description includes the following media information: 284 o The type of media (video, audio, etc.) 286 o The media transport protocol (RTP/UDP/IP, H.320, etc.) 288 o The format of the media (H.261 video, MPEG video, etc.) 289 In addition to media format and transport protocol, SDP conveys 290 address and port details. For an IP multicast session, these 291 comprise: 293 o The multicast group address for media 295 o The transport port for media 297 This address and port are the destination address and destination 298 port of the multicast stream, whether being sent, received, or both. 300 For unicast IP sessions, the following are conveyed: 302 o The remote address for media 304 o The remote transport port for media 306 The semantics of this address and port depend on the media and 307 transport protocol defined. By default, this SHOULD be the remote 308 address and remote port to which data is sent. Some media types may 309 redefine this behaviour, but this is NOT RECOMMENDED since it 310 complicates implementations (including middleboxes that must parse 311 the addresses to open Network Address Translation (NAT) or firewall 312 pinholes). 314 4.2. Timing Information 316 Sessions may be either bounded or unbounded in time. Whether or not 317 they are bounded, they may be only active at specific times. SDP can 318 convey: 320 o An arbitrary list of start and stop times bounding the session 322 o For each bound, repeat times such as "every Wednesday at 10am for 323 one hour" 325 This timing information is globally consistent, irrespective of local 326 time zone or daylight saving time (see Section 5.9). 328 4.3. Obtaining Further Information about a Session 330 A session description could convey enough information to decide 331 whether or not to participate in a session. SDP may include 332 additional pointers in the form of Uniform Resource Identifiers 333 (URIs) for more information about the session. 335 4.4. Categorisation 337 When many session descriptions are being distributed by SAP, or any 338 other advertisement mechanism, it may be desirable to filter session 339 announcements that are of interest from those that are not. SDP 340 supports a categorisation mechanism for sessions that is capable of 341 being automated (the "a=cat:" attribute; see Section 6). 343 4.5. Internationalisation 345 The SDP specification recommends the use of the ISO 10646 character 346 set in the UTF-8 encoding [RFC3629] to allow many different languages 347 to be represented. However, to assist in compact representations, 348 SDP also allows other character sets such as ISO 8859-1 to be used 349 when desired. Internationalisation only applies to free-text fields 350 (session name and background information), and not to SDP as a whole. 352 5. SDP Specification 354 An SDP description is denoted by the media type "application/sdp" 355 (See Section 8). 357 An SDP description is entirely textual. SDP field names and 358 attribute names use only the US-ASCII subset of UTF-8, but textual 359 fields and attribute values MAY use the full ISO 10646 character set 360 in UTF-8 encoding, or some other character set defined by the 361 "a=charset:" attribute. Field and attribute values that use the full 362 UTF-8 character set are never directly compared, hence there is no 363 requirement for UTF-8 normalisation. The textual form, as opposed to 364 a binary encoding such as ASN.1 or XDR, was chosen to enhance 365 portability, to enable a variety of transports to be used, and to 366 allow flexible, text-based toolkits to be used to generate and 367 process session descriptions. However, since SDP may be used in 368 environments where the maximum permissible size of a session 369 description is limited, the encoding is deliberately compact. Also, 370 since announcements may be transported via very unreliable means or 371 damaged by an intermediate caching server, the encoding was designed 372 with strict order and formatting rules so that most errors would 373 result in malformed session announcements that could be detected 374 easily and discarded. This also allows rapid discarding of encrypted 375 session announcements for which a receiver does not have the correct 376 key. 378 An SDP description consists of a number of lines of text of the form: 380 = 382 where MUST be exactly one case-significant character and 383 is structured text whose format depends on . In 384 general, is either a number of fields delimited by a single 385 space character or a free format string, and is case-significant 386 unless a specific field defines otherwise. Whitespace MUST NOT be 387 used on either side of the "=" sign. 389 An SDP description consists of a session-level section followed by 390 zero or more media-level sections. The session-level part starts 391 with a "v=" line and continues to the first media-level section (or 392 the end of the whole description, whichever comes first). Each 393 media-level section starts with an "m=" line and continues to the 394 next media-level section or the end of the whole session description 395 - whichever comes first. In general, session-level values are the 396 default for all media unless overridden by an equivalent media-level 397 value. 399 Some lines in each description are REQUIRED and some are OPTIONAL, 400 but all MUST appear in exactly the order given here (the fixed order 401 greatly enhances error detection and allows for a simple parser). 402 OPTIONAL items are marked with a "*". 404 Session description 405 v= (protocol version) 406 o= (originator and session identifier) 407 s= (session name) 408 i=* (session information) 409 u=* (URI of description) 410 e=* (email address) 411 p=* (phone number) 412 c=* (connection information -- not required if included in 413 all media descriptions) 414 b=* (zero or more bandwidth information lines) 415 One or more time descriptions ("t=" and "r=" lines; see below) 416 z=* (time zone adjustments) 417 k=* (encryption key) 418 a=* (zero or more session attribute lines) 419 Zero or more media descriptions 421 Time description 422 t= (time the session is active) 423 r=* (zero or more repeat times) 425 Media description, if present 426 m= (media name and transport address) 427 i=* (media title) 428 c=* (connection information -- optional if included at 429 session level) 430 b=* (zero or more bandwidth information lines) 431 k=* (encryption key) 432 a=* (zero or more media attribute lines) 434 The set of type letters is deliberately small and not intended to be 435 extensible -- an SDP parser MUST completely ignore any session 436 description that contains a type letter that it does not understand. 437 The attribute mechanism ("a=" described below) is the primary means 438 for extending SDP and tailoring it to particular applications or 439 media. Some attributes (the ones listed in Section 6 of this memo) 440 have a defined meaning, but others may be added on an application-, 441 media-, or session-specific basis. An SDP parser MUST ignore any 442 attribute it doesn't understand. 444 An SDP description may contain URIs that reference external content 445 in the "u=", "k=", and "a=" lines. These URIs may be dereferenced in 446 some cases, making the session description non-self- contained. 448 The connection ("c=") information in the session-level section 449 applies to all the media of that session unless overridden by 450 connection information in the media description. For instance, in 451 the example below, each audio media description behaves as if it were 452 given a "c=IN IP4 233.252.0.2". 454 An example SDP description is: 456 v=0 457 o=jdoe 2890844526 2890842807 IN IP4 198.51.100.1 458 s=SDP Seminar 459 i=A Seminar on the session description protocol 460 u=http://www.example.com/seminars/sdp.pdf 461 e=j.doe@example.com (Jane Doe) 462 c=IN IP4 233.252.0.2 463 t=2873397496 2873404696 464 a=recvonly 465 m=audio 49170 RTP/AVP 0 466 m=audio 49180 RTP/AVP 0 467 m=video 51372 RTP/AVP 99 468 c=IN IP4 233.252.0.1/127 469 a=rtpmap:99 h263-1998/90000 471 Text fields such as the session name and information are octet 472 strings that may contain any octet with the exceptions of 0x00 (Nul), 473 0x0a (ASCII newline), and 0x0d (ASCII carriage return). The sequence 474 CRLF (0x0d0a) is used to end a record, although parsers SHOULD be 475 tolerant and also accept records terminated with a single newline 476 character. If the "a=charset" attribute is not present, these octet 477 strings MUST be interpreted as containing ISO-10646 characters in 478 UTF-8 encoding (the presence of the "a=charset" attribute may force 479 some fields to be interpreted differently). 481 A session description can contain domain names in the "o=", "u=", 482 "e=", "c=", and "a=" lines. Any domain name used in SDP MUST comply 483 with [RFC1034], [RFC1035]. Internationalised domain names (IDNs) 484 MUST be represented using the ASCII Compatible Encoding (ACE) form 485 defined in [RFC5890] and MUST NOT be directly represented in UTF-8 or 486 any other encoding (this requirement is for compatibility with 487 [RFC2327] and other early SDP-related standards, which predate the 488 development of internationalised domain names). 490 5.1. Protocol Version ("v=") 492 v=0 494 The "v=" line gives the version of the Session Description Protocol. 495 This memo defines version 0. There is no minor version number. 497 5.2. Origin ("o=") 499 o= 500 502 The "o=" line gives the originator of the session (her username and 503 the address of the user's host) plus a session identifier and version 504 number: 506 is the user's login on the originating host, or it is "-" 507 if the originating host does not support the concept of user IDs. 508 The MUST NOT contain spaces. 510 is a numeric string such that the tuple of , 511 , , , and forms a 512 globally unique identifier for the session. The method of allocation is up to the creating tool, but it has been 514 suggested that a Network Time Protocol (NTP) format timestamp be 515 used to ensure uniqueness [RFC5905]. 517 is a version number for this session description. 518 Its usage is up to the creating tool, so long as is 519 increased when a modification is made to the session data. Again, 520 it is RECOMMENDED that an NTP format timestamp is used. 522 is a text string giving the type of network. Initially 523 "IN" is defined to have the meaning "Internet", but other values 524 MAY be registered in the future (see Section 8). 526 is a text string giving the type of the address that 527 follows. Initially "IP4" and "IP6" are defined, but other values 528 MAY be registered in the future (see Section 8). 530 is an address of the machine from which the 531 session was created. For an address type of IP4, this is either a 532 fully qualified domain name of the machine or the dotted-decimal 533 representation of an IP version 4 address of the machine. For an 534 address type of IP6, this is either a fully qualified domain name 535 of the machine or the compressed textual representation of an IP 536 version 6 address of the machine. For both IP4 and IP6, the fully 537 qualified domain name is the form that SHOULD be given unless this 538 is unavailable, in which case a globally unique address MAY be 539 substituted. Unless an SDP extension for NAT traversal is used 540 (e.g., ICE [RFC5245], ICE TCP [RFC6544]), a local IP address MUST 541 NOT be used in any context where the SDP description might leave 542 the scope in which the address is meaningful (for example, a local 543 address MUST NOT be included in an application-level referral that 544 might leave the scope). 546 In general, the "o=" line serves as a globally unique identifier for 547 this version of this session description, and the subfields excepting 548 the version taken together identify the session irrespective of any 549 modifications. 551 For privacy reasons, it is sometimes desirable to obfuscate the 552 username and IP address of the session originator. If this is a 553 concern, an arbitrary and private MAY be 554 chosen to populate the "o=" line, provided that these are selected in 555 a manner that does not affect the global uniqueness of the field. 557 5.3. Session Name ("s=") 559 s= 561 The "s=" line is the textual session name. There MUST be one and 562 only one "s=" line per session description. The "s=" line MUST NOT 563 be empty and SHOULD contain ISO 10646 characters (but see also the 564 "a=charset" attribute). If a session has no meaningful name, the 565 value "s= " SHOULD be used (i.e., a single space as the session 566 name). 568 5.4. Session Information ("i=") 570 i= 572 The "i=" line provides textual information about the session. There 573 MUST be at most one session-level "i=" line per session description, 574 and at most one "i=" line per media description/definition. Unless a 575 media level "i="" line is used, the session-level "i="" line applies 576 to that media description. If the "a=charset" attribute is present, 577 it specifies the character set used in the "i=" line. If the 578 "a=charset" attribute is not present, the "i=" line MUST contain ISO 579 10646 characters in UTF-8 encoding. 581 A single "i=" line can be used for each media definition. In media 582 definitions, "i=" lines are primarily intended for labelling media 583 streams. As such, they are most likely to be useful when a single 584 session has more than one distinct media stream of the same media 585 type. An example would be two different whiteboards, one for slides 586 and one for feedback and questions. 588 The "i=" line is intended to provide a free-form human-readable 589 description of the session or the purpose of a media stream. It is 590 not suitable for parsing by automata. 592 5.5. URI ("u=") 594 u= 596 A URI is a Uniform Resource Identifier as used by WWW clients 597 [RFC3986]. The URI should be a pointer to additional information 598 about the session. This line is OPTIONAL. No more than one URI line 599 is allowed per session description. 601 5.6. Email Address and Phone Number ("e=" and "p=") 603 e= 604 p= 606 The "e=" and "p=" lines specify contact information for the person 607 responsible for the session. This is not necessarily the same person 608 that created the session description. 610 Inclusion of an email address or phone number is OPTIONAL. 612 If an email address or phone number is present, it MUST be specified 613 before the first media field. More than one email or phone line can 614 be given for a session description. 616 Phone numbers SHOULD be given in the form of an international public 617 telecommunication number (see ITU-T Recommendation E.164) preceded by 618 a "+". Spaces and hyphens may be used to split up a phone field to 619 aid readability if desired. For example: 621 p=+1 617 555-6011 623 Both email addresses and phone numbers can have an OPTIONAL free text 624 string associated with them, normally giving the name of the person 625 who may be contacted. This MUST be enclosed in parentheses if it is 626 present. For example: 628 e=j.doe@example.com (Jane Doe) 630 The alternative [RFC5322] name quoting convention is also allowed for 631 both email addresses and phone numbers. For example: 633 e=Jane Doe 635 The free text string SHOULD be in the ISO-10646 character set with 636 UTF-8 encoding, or alternatively in ISO-8859-1 or other encodings if 637 the appropriate session-level "a=charset" attribute is set. 639 5.7. Connection Data ("c=") 641 c= 643 The "c=" line contains connection data. 645 A session description MUST contain either at least one "c=" line in 646 each media description or a single "c=" line at the session level. 647 It MAY contain a single session-level "c=" line and additional "c=" 648 line(s) per media description, in which case the per-media values 649 override the session-level settings for the respective media. 651 The first sub-field ("") is the network type, which is a 652 text string giving the type of network. Initially, "IN" is defined 653 to have the meaning "Internet", but other values MAY be registered in 654 the future (see Section 8). 656 The second sub-field ("") is the address type. This allows 657 SDP to be used for sessions that are not IP based. This memo only 658 defines IP4 and IP6, but other values MAY be registered in the future 659 (see Section 8). 661 The third sub-field ("") is the connection 662 address. OPTIONAL sub-fields MAY be added after the connection 663 address depending on the value of the field. 665 When the is IP4 and IP6, the connection address is defined 666 as follows: 668 o If the session is multicast, the connection address will be an IP 669 multicast group address. If the session is not multicast, then 670 the connection address contains the unicast IP address of the 671 expected data source or data relay or data sink as determined by 672 additional attribute fields. It is not expected that unicast 673 addresses will be given in a session description that is 674 communicated by a multicast announcement, though this is not 675 prohibited. 677 o Sessions using an IP4 multicast connection address MUST also have 678 a time to live (TTL) value present in addition to the multicast 679 address. The TTL and the address together define the scope with 680 which multicast packets sent in this session will be sent. TTL 681 values MUST be in the range 0-255. Although the TTL MUST be 682 specified, its use to scope multicast traffic is deprecated; 683 applications SHOULD use an administratively scoped address 684 instead. 686 The TTL for the session is appended to the address using a slash as a 687 separator. An example is: 689 c=IN IP4 233.252.0.1/127 691 IP6 multicast does not use TTL scoping, and hence the TTL value MUST 692 NOT be present for IP6 multicast. It is expected that IP6 scoped 693 addresses will be used to limit the scope of multimedia conferences. 695 Hierarchical or layered encoding schemes are data streams where the 696 encoding from a single media source is split into a number of layers. 697 The receiver can choose the desired quality (and hence bandwidth) by 698 only subscribing to a subset of these layers. Such layered encodings 699 are normally transmitted in multiple multicast groups to allow 700 multicast pruning. This technique keeps unwanted traffic from sites 701 only requiring certain levels of the hierarchy. For applications 702 requiring multiple multicast groups, we allow the following notation 703 to be used for the connection address: 705 [/]/ 707 If the number of addresses is not given, it is assumed to be one. 708 Multicast addresses so assigned are contiguously allocated above the 709 base address, so that, for example: 711 c=IN IP4 233.252.0.1/127/3 713 would state that addresses 233.252.0.1, 233.252.0.2, and 233.252.0.3 714 are to be used at a TTL of 127. This is semantically identical to 715 including multiple "c=" lines in a media description: 717 c=IN IP4 233.252.0.1/127 718 c=IN IP4 233.252.0.2/127 719 c=IN IP4 233.252.0.3/127 721 Similarly, an IP6 example would be: 723 c=IN IP6 FF15::101/3 725 which is semantically equivalent to: 727 c=IN IP6 FF15::101 728 c=IN IP6 FF15::102 729 c=IN IP6 FF15::103 731 (remembering that the TTL field is not present in IP6 multicast). 733 Multiple addresses or "c=" lines MAY be specified on a per-media 734 basis only if they provide multicast addresses for different layers 735 in a hierarchical or layered encoding scheme. They MUST NOT be 736 specified for a session-level "c=" line. 738 The slash notation for multiple addresses described above MUST NOT be 739 used for IP unicast addresses. 741 5.8. Bandwidth ("b=") 743 b=: 745 This OPTIONAL line denotes the proposed bandwidth to be used by the 746 session or media. The is an alphanumeric modifier giving 747 the meaning of the figure. Two values are defined in 748 this specification, but other values MAY be registered in the future 749 (see Section 8 and [RFC3556], [RFC3890]): 751 CT If the bandwidth of a session is different from the bandwidth 752 implicit from the scope, a "b=CT:..." line SHOULD be supplied for 753 the session giving the proposed upper limit to the bandwidth used 754 (the "conference total" bandwidth). Similarly, if the bandwidth 755 of bundled media streams in an m line is different from the 756 implicit value from the scope, a "b=CT:..." line SHOULD be 757 supplied in the media level. The primary purpose of this is to 758 give an approximate idea as to whether two or more sessions (or 759 bundled media streams) can coexist simultaneously. Note that CT 760 gives a total bandwidth figure for all the media at all endpoints. 762 AS The bandwidth is interpreted to be application specific (it will 763 be the application's concept of maximum bandwidth). Normally, 764 this will coincide with what is set on the application's "maximum 765 bandwidth" control if applicable. For RTP-based applications, AS 766 gives the RTP "session bandwidth" as defined in Section 6.2 of 767 [RFC3550]. Note that AS gives a bandwidth figure for a single 768 media at a single endpoint, although there may be many endpoints 769 sending simultaneously. 771 A prefix "X-" is defined for names. This is intended for 772 experimental purposes only. For example: 774 b=X-YZ:128 776 Use of the "X-" prefix is NOT RECOMMENDED: instead new modifiers 777 SHOULD be registered with IANA in the standard namespace. SDP 778 parsers MUST ignore bandwidth fields with unknown modifiers. 779 Modifiers MUST be alphanumeric and, although no length limit is 780 given, it is recommended that they be short. 782 The is interpreted as kilobits per second by default. 783 The definition of a new modifier MAY specify that the 784 bandwidth is to be interpreted in some alternative unit (the "CT" and 785 "AS" modifiers defined in this memo use the default units). 787 5.9. Timing ("t=") 789 t= 791 The "t=" lines specify the start and stop times for a session. 792 Multiple "t=" lines MAY be used if a session is active at multiple 793 irregularly spaced times; each additional "t=" line specifies an 794 additional period of time for which the session will be active. If 795 the session is active at regular times, an "r=" line (see below) 796 should be used in addition to, and following, a "t=" line -- in which 797 case the "t=" line specifies the start and stop times of the repeat 798 sequence. 800 The first and second sub-fields give the start and stop times, 801 respectively, for the session. These values are the decimal 802 representation of Network Time Protocol (NTP) time values in seconds 803 since 1900 [RFC5905]. To convert these values to UNIX time, subtract 804 decimal 2208988800. 806 NTP timestamps are elsewhere represented by 64-bit values, which wrap 807 sometime in the year 2036. Since SDP uses an arbitrary length 808 decimal representation, this should not cause an issue (SDP 809 timestamps MUST continue counting seconds since 1900, NTP will use 810 the value modulo the 64-bit limit). 812 If the is set to zero, then the session is not bounded, 813 though it will not become active until after the . If 814 the is also zero, the session is regarded as permanent. 816 User interfaces SHOULD strongly discourage the creation of unbounded 817 and permanent sessions as they give no information about when the 818 session is actually going to terminate, and so make scheduling 819 difficult. 821 The general assumption may be made, when displaying unbounded 822 sessions that have not timed out to the user, that an unbounded 823 session will only be active until half an hour from the current time 824 or the session start time, whichever is the later. If behaviour 825 other than this is required, an end-time SHOULD be given and modified 826 as appropriate when new information becomes available about when the 827 session should really end. 829 Permanent sessions may be shown to the user as never being active 830 unless there are associated repeat times that state precisely when 831 the session will be active. 833 5.10. Repeat Times ("r=") 835 r= 837 "r=" line specifies repeat times for a session. For example, if a 838 session is active at 10am on Monday and 11am on Tuesday for one hour 839 each week for three months, then the in the 840 corresponding "t=" line would be the NTP representation of 10am on 841 the first Monday, the would be 1 week, the would be 1 hour, and the offsets would be zero and 25 843 hours. The corresponding "t=" line stop time would be the NTP 844 representation of the end of the last session three months later. By 845 default, all fields are in seconds, so the "r=" and "t=" lines might 846 be the following: 848 t=3034423619 3042462419 849 r=604800 3600 0 90000 851 To make the description more compact, times may also be given in 852 units of days, hours, or minutes. The syntax for these is a number 853 immediately followed by a single case-sensitive character. 854 Fractional units are not allowed -- a smaller unit should be used 855 instead. The following unit specification characters are allowed: 857 d - days (86400 seconds) 858 h - hours (3600 seconds) 859 m - minutes (60 seconds) 860 s - seconds (allowed for completeness) 862 Thus, the above session announcement could also have been written: 864 r=7d 1h 0 25h 866 Monthly and yearly repeats cannot be directly specified with a single 867 SDP repeat time; instead, separate "t=" lines should be used to 868 explicitly list the session times. 870 5.11. Time Zones ("z=") 872 z= .... 874 To schedule a repeated session that spans a change from daylight 875 saving time to standard time or vice versa, it is necessary to 876 specify offsets from the base time. This is required because 877 different time zones change time at different times of day, different 878 countries change to or from daylight saving time on different dates, 879 and some countries do not have daylight saving time at all. 881 Thus, in order to schedule a session that is at the same time winter 882 and summer, it must be possible to specify unambiguously by whose 883 time zone a session is scheduled. To simplify this task for 884 receivers, we allow the sender to specify the NTP time that a time 885 zone adjustment happens and the offset from the time when the session 886 was first scheduled. The "z=" line allows the sender to specify a 887 list of these adjustment times and offsets from the base time. 889 An example might be the following: 891 z=2882844526 -1h 2898848070 0 893 This specifies that at time 2882844526, the time base by which the 894 session's repeat times are calculated is shifted back by 1 hour, and 895 that at time 2898848070, the session's original time base is 896 restored. Adjustments are always relative to the specified start 897 time -- they are not cumulative. Adjustments apply to all "t=" and 898 "r=" lines in a session description. 900 If a session is likely to last several years, it is expected that the 901 session description will be modified periodically rather than 902 transmit several years' worth of adjustments in one session 903 description. 905 5.12. Encryption Keys ("k=") 907 k= 908 k=: 910 If transported over a secure and trusted channel, the Session 911 Description Protocol MAY be used to convey encryption keys. A simple 912 mechanism for key exchange is provided by the key line ("k="), 913 although this is primarily supported for compatibility with older 914 implementations and its use is NOT RECOMMENDED. Work is in progress 915 to define new key exchange mechanisms for use with SDP [RFC4567] 916 [RFC4568], and it is expected that new applications will use those 917 mechanisms. 919 A key line is permitted before the first media entry (in which case 920 it applies to all media in the session), or for each media entry as 921 required. The format of keys and their usage are outside the scope 922 of this document, and the key field provides no way to indicate the 923 encryption algorithm to be used, key type, or other information about 924 the key: this is assumed to be provided by the higher-level protocol 925 using SDP. If there is a need to convey this information within SDP, 926 the extensions mentioned previously SHOULD be used. Many security 927 protocols require two keys: one for confidentiality, another for 928 integrity. This specification does not support transfer of two keys. 930 The method indicates the mechanism to be used to obtain a usable key 931 by external means, or from the encoded encryption key given. The 932 following methods are defined: 934 k=clear: 936 The encryption key is included untransformed in this key line. 937 This method MUST NOT be used unless it can be guaranteed that 938 the SDP is conveyed over a secure channel. The encryption key 939 is interpreted as text according to the charset attribute; use 940 the "k=base64:" method to convey characters that are otherwise 941 prohibited in SDP. 943 k=base64: 945 The encryption key is included in this key line but has been 946 base64 encoded [RFC4648] because it includes characters that 947 are prohibited in SDP. This method MUST NOT be used unless it 948 can be guaranteed that the SDP is conveyed over a secure 949 channel. 951 k=uri: 953 A Uniform Resource Identifier is included in the key line. The 954 URI refers to the data containing the key, and may require 955 additional authentication before the key can be returned. When 956 a request is made to the given URI, the reply should specify 957 the encoding for the key. The URI is often an Secure Socket 958 Layer/Transport Layer Security (SSL/TLS)-protected HTTP URI 959 ("https:"), although this is not required. 961 k=prompt 963 No key is included in this SDP description, but the session or 964 media stream referred to by this key line is encrypted. The 965 user should be prompted for the key when attempting to join the 966 session, and this user-supplied key should then be used to 967 decrypt the media streams. The use of user-specified keys is 968 NOT RECOMMENDED, since such keys tend to have weak security 969 properties. 971 The key line MUST NOT be used unless it can be guaranteed that the 972 SDP is conveyed over a secure and trusted channel. An example of 973 such a channel might be SDP embedded inside an S/MIME message or a 974 TLS-protected HTTP session. It is important to ensure that the 975 secure channel is with the party that is authorised to join the 976 session, not an intermediary: if a caching proxy server is used, it 977 is important to ensure that the proxy is either trusted or unable to 978 access the SDP. 980 5.13. Attributes ("a=") 982 a= 983 a=: 985 Attributes are the primary means for extending SDP. Attributes may 986 be defined to be used as "session-level" attributes, "media-level" 987 attributes, or both. 989 A media description may have any number of attributes ("a=" lines) 990 that are media specific. These are referred to as "media-level" 991 attributes and add information about the media stream. Attribute 992 lines can also be added before the first media field; these "session- 993 level" attributes convey additional information that applies to the 994 session as a whole rather than to individual media. 996 Attribute lines may be of two forms: 998 o A property attribute is simply of the form "a=". These are 999 binary attributes, and the presence of the attribute conveys that 1000 the attribute is a property of the session. An example might be 1001 "a=recvonly". 1003 o A value attribute is of the form "a=:". For 1004 example, a whiteboard could have the value attribute 1005 "a=orient:landscape" 1007 Attribute interpretation depends on the media tool being invoked. 1008 Thus receivers of session descriptions should be configurable in 1009 their interpretation of session descriptions in general and of 1010 attributes in particular. 1012 Attribute names MUST use the US-ASCII subset of ISO-10646/UTF-8. 1014 Attribute values are octet strings, and MAY use any octet value 1015 except 0x00 (Nul), 0x0A (LF), and 0x0D (CR). By default, attribute 1016 values are to be interpreted as in ISO-10646 character set with UTF-8 1017 encoding. Unlike other text fields, attribute values are NOT 1018 normally affected by the "charset" attribute as this would make 1019 comparisons against known values problematic. However, when an 1020 attribute is defined, it can be defined to be charset dependent, in 1021 which case its value should be interpreted in the session charset 1022 rather than in ISO-10646. 1024 Attributes MUST be registered with IANA (see Section 8). If an 1025 attribute is received that is not understood, it MUST be ignored by 1026 the receiver. 1028 5.14. Media Descriptions ("m=") 1030 m= ... 1032 A session description may contain a number of media descriptions. 1033 Each media description starts with an "m=" line and is terminated by 1034 either the next "m=" line or by the end of the session description. 1035 A media field has several sub-fields: 1037 is the media type. This document defines the values 1038 "audio", "video", "text", "application", and "message". This list 1039 is extended and may be further extended by other memos registering 1040 media types in the future (see Section 8). 1042 is the transport port to which the media stream is sent. The 1043 meaning of the transport port depends on the network being used as 1044 specified in the relevant "c=" line, and on the transport protocol 1045 defined in the sub-field of the media field. Other ports 1046 used by the media application (such as the RTP Control Protocol 1047 (RTCP) port [RFC3550]) MAY be derived algorithmically from the 1048 base media port or MAY be specified in a separate attribute (for 1049 example, "a=rtcp:" as defined in [RFC3605]). 1051 If non-contiguous ports are used or if they don't follow the 1052 parity rule of even RTP ports and odd RTCP ports, the "a=rtcp:" 1053 attribute MUST be used. Applications that are requested to send 1054 media to a that is odd and where the "a=rtcp:" is present 1055 MUST NOT subtract 1 from the RTP port: that is, they MUST send the 1056 RTP to the port indicated in and send the RTCP to the port 1057 indicated in the "a=rtcp" attribute. 1059 For applications where hierarchically encoded streams are being 1060 sent to a unicast address, it may be necessary to specify multiple 1061 transport ports. This is done using a similar notation to that 1062 used for IP multicast addresses in the "c=" line: 1064 m= / ... 1066 In such a case, the ports used depend on the transport protocol. 1067 For RTP, the default is that only the even-numbered ports are used 1068 for data with the corresponding one-higher odd ports used for the 1069 RTCP belonging to the RTP session, and the 1070 denoting the number of RTP sessions. For example: 1072 m=video 49170/2 RTP/AVP 31 1074 would specify that ports 49170 and 49171 form one RTP/RTCP pair 1075 and 49172 and 49173 form the second RTP/RTCP pair. RTP/AVP is the 1076 transport protocol and 31 is the format (see below). If non- 1077 contiguous ports are required, they must be signalled using a 1078 separate attribute (for example, "a=rtcp:" as defined in 1079 [RFC3605]). 1081 If multiple addresses are specified in the "c=" line and multiple 1082 ports are specified in the "m=" line, a one-to-one mapping from 1083 port to the corresponding address is implied. For example: 1085 c=IN IP4 233.252.0.1/127/2 1086 m=video 49170/2 RTP/AVP 31 1088 would imply that address 233.252.0.1 is used with ports 49170 and 1089 49171, and address 233.252.0.2 is used with ports 49172 and 49173. 1091 The semantics of multiple "m=" lines using the same transport 1092 address are undefined. This implies that, unlike limited past 1093 practice, there is no implicit grouping defined by such means and 1094 an explicit grouping framework (for example, [RFC5888]) should 1095 instead be used to express the intended semantics. 1097 is the transport protocol. The meaning of the transport 1098 protocol is dependent on the address type field in the relevant 1099 "c=" line. Thus a "c=" field of IP4 indicates that the transport 1100 protocol runs over IP4. The following transport protocols are 1101 defined, but may be extended through registration of new protocols 1102 with IANA (see Section 8): 1104 * udp: denotes an unspecified protocol running over UDP. 1106 * RTP/AVP: denotes RTP [RFC3550] used under the RTP Profile for 1107 Audio and Video Conferences with Minimal Control [RFC3551] 1108 running over UDP. 1110 * RTP/SAVP: denotes the Secure Real-time Transport Protocol 1111 [RFC3711] running over UDP. 1113 The main reason to specify the transport protocol in addition to 1114 the media format is that the same standard media formats may be 1115 carried over different transport protocols even when the network 1116 protocol is the same -- a historical example is vat Pulse Code 1117 Modulation (PCM) audio and RTP PCM audio; another might be TCP/RTP 1118 PCM audio. In addition, relays and monitoring tools that are 1119 transport-protocol-specific but format-independent are possible. 1121 is a media format description. The fourth and any subsequent 1122 sub-fields describe the format of the media. The interpretation 1123 of the media format depends on the value of the sub-field. 1125 If the sub-field is "RTP/AVP" or "RTP/SAVP" the sub- 1126 fields contain RTP payload type numbers. When a list of payload 1127 type numbers is given, this implies that all of these payload 1128 formats MAY be used in the session, but the first of these formats 1129 SHOULD be used as the default format for the session. For dynamic 1130 payload type assignments the "a=rtpmap:" attribute (see Section 6) 1131 SHOULD be used to map from an RTP payload type number to a media 1132 encoding name that identifies the payload format. The "a=fmtp:" 1133 attribute MAY be used to specify format parameters (see 1134 Section 6). 1136 If the sub-field is "udp" the sub-fields MUST 1137 reference a media type describing the format under the "audio", 1138 "video", "text", "application", or "message" top-level media 1139 types. The media type registration SHOULD define the packet 1140 format for use with UDP transport. 1142 For media using other transport protocols, the field is 1143 protocol specific. Rules for interpretation of the sub- 1144 field MUST be defined when registering new protocols (see 1145 Section 8.2.2). 1147 Section 3 of [RFC4855] states that the payload format (encoding) 1148 names defined in the RTP Profile are commonly shown in upper case, 1149 while media subtype names are commonly shown in lower case. It 1150 also states that both of these names are case-insensitive in both 1151 places, similar to parameter names which are case-insensitive both 1152 in media type strings and in the default mapping to the SDP a=fmtp 1153 attribute. 1155 6. SDP Attributes 1157 The following attributes are defined. Since application writers may 1158 add new attributes as they are required, this list is not exhaustive. 1159 Registration procedures for new attributes are defined in 1160 Section 8.2.4. 1162 6.1. cat (category) 1164 Name: cat 1166 Value: cat-value 1168 Usage Level: session 1170 Charset Dependent: no 1172 Syntax: 1174 cat-value = category 1175 category = non-ws-string 1177 Example: 1179 a=cat:foo.bar 1181 This attribute gives the dot-separated hierarchical category of the 1182 session. This is to enable a receiver to filter unwanted sessions by 1183 category. There is no central registry of categories. This 1184 attribute is obsoleted. 1186 6.2. keywds (keywords) 1188 Name: keywds 1190 Value: keywds-value 1192 Usage Level: session 1194 Charset Dependent: yes 1196 Syntax: 1198 keywds-value = keywords 1199 keywords = text 1201 Example: 1203 a=keywds:SDP session description protocol 1205 Like the cat attribute, this is to assist identifying wanted sessions 1206 at the receiver. This allows a receiver to select interesting 1207 session based on keywords describing the purpose of the session; 1208 there is no central registry of keywords. Its value should be 1209 interpreted in the charset specified for the session description if 1210 one is specified, or by default in ISO 10646/UTF-8. This attribute 1211 is obsoleted. 1213 6.3. tool 1215 Name: tool 1217 Value: tool-value 1219 Usage Level: session 1221 Charset Dependent: no 1223 Syntax: 1225 tool-value = tool-name-and-version 1226 tool-name-and-version = text 1228 Example: 1230 a=tool:foobar V3.2 1232 This gives the name and version number of the tool used to create the 1233 session description. 1235 6.4. ptime (packet time) 1237 Name: ptime 1239 Value: ptime-value 1241 Usage Level: media 1243 Charset Dependent: no 1245 Syntax: 1247 ptime-value = non-zero-int-or-real 1249 Example: 1251 a=ptime:20 1253 This gives the length of time in milliseconds represented by the 1254 media in a packet. This is probably only meaningful for audio data, 1255 but may be used with other media types if it makes sense. It should 1256 not be necessary to know ptime to decode RTP or vat audio, and it is 1257 intended as a recommendation for the encoding/packetisation of audio. 1259 6.5. maxptime (maximum packet time) 1261 Name: maxptime 1263 Value: maxptime-value 1265 Usage Level: media 1267 Charset Dependent: no 1269 Syntax: 1271 maxptime-value = non-zero-int-or-real 1273 Example: 1275 a=maxptime:20 1277 This gives the maximum amount of media that can be encapsulated in 1278 each packet, expressed as time in milliseconds. The time SHALL be 1279 calculated as the sum of the time the media present in the packet 1280 represents. For frame-based codecs, the time SHOULD be an integer 1281 multiple of the frame size. This attribute is probably only 1282 meaningful for audio data, but may be used with other media types if 1283 it makes sense. Note that this attribute was introduced after 1284 [RFC2327], and non-updated implementations will ignore this 1285 attribute. 1287 6.6. rtpmap 1289 Name: rtpmap 1291 Value: rtpmap-value 1293 Usage Level: media 1295 Charset Dependent: no 1296 Syntax: 1298 rtpmap-value = payload-type SP encoding-name 1299 "/" clock-rate [ "/" encoding-params ] 1300 payload-type = zero-based-integer 1301 encoding-name = token 1302 clock-rate = integer 1303 ; do we want to define a limited range for this? 1304 encoding-params = channels 1305 ; 4566 is vague about what this can be. RFC4855 seems to be 1306 ; the authoritative source, and only allows the 1307 ; value of the media subtype "channels" parameter - the 1308 ; number of audio channels. 1309 ; Does anyone think this can be used for something else??? 1310 ; (The implication that multiple parameters might be included 1311 ; seems a misdirection - additional parameters are 1312 ; to go into a=fmtp.) 1313 ; Does anyone have an example of other parameters 1314 ; using this field? 1315 channels = integer 1316 ; Is there any reason to make this less restrictive? 1318 This attribute maps from an RTP payload type number (as used in an 1319 "m=" line) to an encoding name denoting the payload format to be 1320 used. It also provides information on the clock rate and encoding 1321 parameters. Note that the payload type number is indicated in a 1322 7-bit field, limiting the values to incusively between 0 and 127. 1324 Although an RTP profile can make static assignments of payload type 1325 numbers to payload formats, it is more common for that assignment to 1326 be done dynamically using "a=rtpmap:" attributes. As an example of a 1327 static payload type, consider u-law PCM coded single-channel audio 1328 sampled at 8 kHz. This is completely defined in the RTP Audio/Video 1329 profile as payload type 0, so there is no need for an "a=rtpmap:" 1330 attribute, and the media for such a stream sent to UDP port 49232 can 1331 be specified as: 1333 m=audio 49232 RTP/AVP 0 1335 An example of a dynamic payload type is 16-bit linear encoded stereo 1336 audio sampled at 16 kHz. If we wish to use the dynamic RTP/AVP 1337 payload type 98 for this stream, additional information is required 1338 to decode it: 1340 m=audio 49232 RTP/AVP 98 1341 a=rtpmap:98 L16/16000/2 1343 Up to one rtpmap attribute can be defined for each media format 1344 specified. Thus, we might have the following: 1346 m=audio 49230 RTP/AVP 96 97 98 1347 a=rtpmap:96 L8/8000 1348 a=rtpmap:97 L16/8000 1349 a=rtpmap:98 L16/11025/2 1351 RTP profiles that specify the use of dynamic payload types MUST 1352 define the set of valid encoding names and/or a means to register 1353 encoding names if that profile is to be used with SDP. The "RTP/AVP" 1354 and "RTP/SAVP" profiles use media subtypes for encoding names, under 1355 the top-level media type denoted in the "m=" line. In the example 1356 above, the media types are "audio/l8" and "audio/l16". 1358 For audio streams, indicates the number of 1359 audio channels. This parameter is OPTIONAL and may be omitted if the 1360 number of channels is one, provided that no additional parameters are 1361 needed. 1363 For video streams, no encoding parameters are currently specified. 1365 Additional encoding parameters MAY be defined in the future, but 1366 codec-specific parameters SHOULD NOT be added. Parameters added to 1367 an "a=rtpmap:" attribute SHOULD only be those required for a session 1368 directory to make the choice of appropriate media to participate in a 1369 session. Codec-specific parameters should be added in other 1370 attributes (for example, "a=fmtp:"). 1372 Note: RTP audio formats typically do not include information about 1373 the number of samples per packet. If a non-default (as defined in 1374 the RTP Audio/Video Profile) packetisation is required, the "ptime" 1375 attribute is used as given above. 1377 6.7. Media Direction Attributes 1379 At most one of recvonly/sendrecv/sendonly/inactive MAY appear at 1380 session level, and at most one MAY appear in each media section. 1382 If any one of these appears in a media section then it applies for 1383 that media section. If none appear in a media section then the one 1384 from session level, if any, applies to that media section. 1386 If none of the media direction attributes is present at either 1387 session level or media level, "sendrecv" SHOULD be assumed as the 1388 default for sessions that are not of the multimedia conference type 1389 "broadcast" or "H332" (see below). 1391 Within the following SDP example, the "inactive" attribute applies to 1392 audio media and the "recvonly" attribute applies to video media. 1394 v=0 1395 o=jdoe 2890844526 2890842807 IN IP4 198.51.100.1 1396 s=SDP Seminar 1397 i=A Seminar on the session description protocol 1398 u=http://www.example.com/seminars/sdp.pdf 1399 e=j.doe@example.com (Jane Doe) 1400 c=IN IP4 233.252.0.1/127 1401 t=2873397496 2873404696 1402 a=inactive 1403 m=audio 49170 RTP/AVP 0 1404 m=video 51372 RTP/AVP 99 1405 a=rtpmap:99 h263-1998/90000 1406 a=recvonly 1408 6.7.1. recvonly (receive-only) 1410 Name: recvonly 1412 Value: 1414 Usage Level: session, media 1416 Charset Dependent: no 1418 Example: 1420 a=recvonly 1422 This specifies that the tools should be started in receive-only mode 1423 where applicable. Note that recvonly applies to the media only, not 1424 to any associated control protocol (e.g., an RTP-based system in 1425 recvonly mode SHOULD still send RTCP packets). 1427 6.7.2. sendrecv (send-receive) 1429 Name: sendrecv 1431 Value: 1433 Usage Level: session, media 1435 Charset Dependent: no 1436 Example: 1438 a=sendrecv 1440 This specifies that the tools should be started in send and receive 1441 mode. This is necessary for interactive multimedia conferences with 1442 tools that default to receive-only mode. 1444 6.7.3. sendonly (send-only) 1446 Name: sendonly 1448 Value: 1450 Usage Level: session, media 1452 Charset Dependent: no 1454 Example: 1456 a=sendonly 1458 This specifies that the tools should be started in send-only mode. 1459 An example may be where a different unicast address is to be used for 1460 a traffic destination than for a traffic source. In such a case, two 1461 media descriptions may be used, one sendonly and one recvonly. Note 1462 that sendonly applies only to the media, and any associated control 1463 protocol (e.g., RTCP) SHOULD still be received and processed as 1464 normal. 1466 6.7.4. inactive 1468 Name: inactive 1470 Value: 1472 Usage Level: session, media 1474 Charset Dependent: no 1476 Example: 1478 a=inactive 1480 This specifies that the tools should be started in inactive mode. 1481 This is necessary for interactive multimedia conferences where users 1482 can put other users on hold. No media is sent over an inactive media 1483 stream. Note that an RTP-based system MUST still send RTCP (if RTCP 1484 is used), even if started inactive. 1486 6.8. orient (orientation) 1488 Name: orient 1490 Value: orient-value 1492 Usage Level: media 1494 Charset Dependent: no 1496 Syntax: 1498 orient-value = portrait / landscape / seascape 1499 portrait = %s"portrait" 1500 landscape = %s"landscape" 1501 seascape = %s"seascape" 1502 ; NOTE: These names are case-sensitive. 1504 Example: 1506 a=orient:portrait 1508 Normally this is only used for a whiteboard or presentation tool. It 1509 specifies the orientation of a the workspace on the screen. 1510 Permitted values are "portrait", "landscape", and "seascape" (upside- 1511 down landscape). 1513 6.9. type (conference type) 1515 Name: type 1517 Value: type-value 1519 Usage Level: session 1521 Charset Dependent: no 1522 Syntax: 1524 type-value = conference-type 1525 conference-type = broadcast / meeting / moderated / test / 1526 H332 1527 broadcast = %s"broadcast" 1528 meeting = %s"meeting" 1529 moderated = %s"moderated" 1530 test = %s"test" 1531 H332 = %s"H332" 1532 ; NOTE: These names are case-sensitive. 1534 Example: 1536 a=type:moderated 1538 This specifies the type of the multimedia conference. Suggested 1539 values are "broadcast", "meeting", "moderated", "test", and "H332". 1540 "recvonly" should be the default for "type:broadcast" sessions, 1541 "type:meeting" should imply "sendrecv", and "type:moderated" should 1542 indicate the use of a floor control tool and that the media tools are 1543 started so as to mute new sites joining the multimedia conference. 1545 Specifying the attribute "type:H332" indicates that this loosely 1546 coupled session is part of an H.332 session as defined in the ITU 1547 H.332 specification [ITU.H332.1998]. Media tools should be started 1548 "recvonly". 1550 Specifying the attribute "type:test" is suggested as a hint that, 1551 unless explicitly requested otherwise, receivers can safely avoid 1552 displaying this session description to users. 1554 6.10. charset (character set) 1556 Name: charset 1558 Value: charset-value 1560 Usage Level: session 1562 Charset Dependent: no 1564 Syntax: 1566 charset-value = mime-charset 1567 (as defined in I-D.iana-charset-reg-procedure) 1569 This specifies the character set to be used to display the session 1570 name and information data. By default, the ISO-10646 character set 1571 in UTF-8 encoding is used. If a more compact representation is 1572 required, other character sets may be used. For example, the ISO 1573 8859-1 is specified with the following SDP attribute: 1575 a=charset:ISO-8859-1 1577 The charset specified MUST be one of those registered in the IANA 1578 Character Sets registry (http://www.iana.org/assignments/character- 1579 sets), such as ISO-8859-1. The character set identifier is a US- 1580 ASCII string and MUST be compared against identifiers from the "Name" 1581 or "Preferred MIME Name" field of the registry using a case- 1582 insensitive comparison. If the identifier is not recognised or not 1583 supported, all strings that are affected by it SHOULD be regarded as 1584 octet strings. 1586 Note that a character set specified MUST still prohibit the use of 1587 bytes 0x00 (Nul), 0x0A (LF), and 0x0d (CR). Character sets requiring 1588 the use of these characters MUST define a quoting mechanism that 1589 prevents these bytes from appearing within text fields. 1591 6.11. sdplang (SDP language) 1593 Name: sdplang 1595 Value: sdplang-value 1597 Usage Level: session, media 1599 Charset Dependent: no 1601 Syntax: 1603 sdplang-value = Language-Tag 1604 ; Language-Tag defined in RFC5646 1606 Example: 1608 a=sdplang:fr 1610 Multiple sdplang attributes can be provided either at session or 1611 media level if the session description or media use multiple 1612 languages. 1614 As a session-level attribute, it specifies the language for the 1615 session description (not the language of the media). As a media- 1616 level attribute, it specifies the language for any media-level SDP 1617 information field associated with that media (again not the language 1618 of the media), overriding any sdplang attributes specified at 1619 session-level. 1621 In general, sending session descriptions consisting of multiple 1622 languages is discouraged. Instead, multiple descriptions SHOULD be 1623 sent describing the session, one in each language. However, this is 1624 not possible with all transport mechanisms, and so multiple sdplang 1625 attributes are allowed although NOT RECOMMENDED. 1627 The "sdplang" attribute value must be a single [RFC5646] language tag 1628 in US-ASCII. An "sdplang" attribute SHOULD be specified when a 1629 session is distributed with sufficient scope to cross geographic 1630 boundaries, where the language of recipients cannot be assumed, or 1631 where the session is in a different language from the locally assumed 1632 norm. 1634 6.12. lang (language) 1636 Name: lang 1638 Value: lang-value 1640 Usage Level: session, media 1642 Charset Dependent: no 1644 Syntax: 1646 lang-value = Language-Tag 1647 ; Language-Tag defined in RFC5646 1649 Example: 1651 a=lang:de 1653 Multiple lang attributes can be provided either at session or media 1654 level if the session or media has capabilities in more than one 1655 language, in which case the order of the attributes indicates the 1656 order of preference of the various languages in the session or media, 1657 from most preferred to least preferred. 1659 As a session-level attribute, lang specifies a language capability 1660 for the session being described. As a media-level attribute, it 1661 specifies a language capability for that media, overriding any 1662 session-level language(s) specified. 1664 The "lang" attribute value must be a single [RFC5646] language tag in 1665 US-ASCII. A "lang" attribute SHOULD be specified when a session is 1666 of sufficient scope to cross geographic boundaries where the language 1667 of participants cannot be assumed, or where the session has 1668 capabilities in languages different from the locally assumed norm. 1670 The "lang" attribute is supposed to be used for settling the initial 1671 language(s) used in the session. Events during the session may 1672 influence which language(s) are used, and the participants are not 1673 strictly bound to only use the declared languages. 1675 Most real-time use cases start with just one language used, while 1676 other cases involve a range of languages, e.g. an interpreted or 1677 subtitled session. When more than one 'lang' attribute is specified, 1678 the "lang" attribute itself does not provide any information about if 1679 multiple languages are intended to be used during the session, or if 1680 the intention is to only select one language. Other attributes or 1681 the semantics in which the "lang" attributes are used might indicate 1682 such conditions. Without such indications of usage intent, it is 1683 assumed that for a negotiated session one of the declared languages 1684 will be selected and used. 1686 6.13. framerate (frame rate) 1688 Name: framerate 1690 Value: framerate-value 1692 Usage Level: media 1694 Charset Dependent: no 1696 Syntax: 1698 framerate-value = non-zero-int-or-real 1700 Example: 1702 a=framerate:60 1704 This gives the maximum video frame rate in frames/sec. It is 1705 intended as a recommendation for the encoding of video data. Decimal 1706 representations of fractional values are allowed. It is defined only 1707 for video media. 1709 6.14. quality 1711 Name: quality 1713 Value: quality-value 1715 Usage Level: media 1717 Charset Dependent: no 1719 Syntax: 1721 quality-value = zero-based-integer 1723 Example: 1725 a=quality:10 1727 This gives a suggestion for the quality of the encoding as an integer 1728 value. The intention of the quality attribute for video is to 1729 specify a non-default trade-off between frame-rate and still-image 1730 quality. For video, the value is in the range 0 to 10, with the 1731 following suggested meaning: 1733 10 - the best still-image quality the compression scheme 1734 can give. 1735 5 - the default behaviour given no quality suggestion. 1736 0 - the worst still-image quality the codec designer 1737 thinks is still usable. 1739 Editor's note: The usage should be checked with the SIP Forum to see 1740 whether anybody is using this. Otherwise, the recommendation will be 1741 not to use this attribute and the receiver ignores it upon reception. 1743 6.15. fmtp (format parameters) 1745 Name: fmtp 1747 Value: fmtp-value 1749 Usage Level: media 1751 Charset Dependent: no 1752 Syntax: 1754 fmtp-value = fmt SP format-specific-params 1755 format-specific-params = byte-string 1756 ; Notes: 1757 ; - The format parameters are media type parameters and 1758 need to reflect their syntax. 1760 Example: 1762 a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600 1764 This attribute allows parameters that are specific to a particular 1765 format to be conveyed in a way that SDP does not have to understand 1766 them. The format must be one of the formats specified for the media. 1767 Format-specific parameters may be any set of parameters required to 1768 be conveyed by SDP and given unchanged to the media tool that will 1769 use this format. At most one instance of this attribute is allowed 1770 for each format. 1772 7. Security Considerations 1774 SDP is frequently used with the Session Initiation Protocol [RFC3261] 1775 using the offer/answer model [RFC3264] to agree on parameters for 1776 unicast sessions. When used in this manner, the security 1777 considerations of those protocols apply. 1779 SDP is a session description format that describes multimedia 1780 sessions. Entities receiving and acting upon an SDP message SHOULD 1781 be aware that a session description cannot be trusted unless it has 1782 been obtained by an authenticated transport protocol from a known and 1783 trusted source. Many different transport protocols may be used to 1784 distribute session descriptions, and the nature of the authentication 1785 will differ from transport to transport. For some transports, 1786 security features are often not deployed. In case a session 1787 description has not been obtained in a trusted manner, the endpoint 1788 SHOULD exercise care because, among other attacks, the media sessions 1789 received may not be the intended ones, the destination where media is 1790 sent to may not be the expected one, any of the parameters of the 1791 session may be incorrect, or the media security may be compromised. 1792 It is up to the endpoint to make a sensible decision taking into 1793 account the security risks of the application and the user 1794 preferences and may decide to ask the user whether or not to accept 1795 the session. 1797 One transport that can be used to distribute session descriptions is 1798 the SAP. SAP provides both encryption and authentication mechanisms, 1799 but due to the nature of session announcements it is likely that 1800 there are many occasions where the originator of a session 1801 announcement cannot be authenticated because the originator is 1802 previously unknown to the receiver of the announcement and because no 1803 common public key infrastructure is available. 1805 On receiving a session description over an unauthenticated transport 1806 mechanism or from an untrusted party, software parsing the session 1807 should take a few precautions. Session descriptions contain 1808 information required to start software on the receiver's system. 1809 Software that parses a session description MUST NOT be able to start 1810 other software except that which is specifically configured as 1811 appropriate software to participate in multimedia sessions. It is 1812 normally considered inappropriate for software parsing a session 1813 description to start, on a user's system, software that is 1814 appropriate to participate in multimedia sessions, without the user 1815 first being informed that such software will be started and giving 1816 the user's consent. Thus, a session description arriving by session 1817 announcement, email, session invitation, or WWW page MUST NOT deliver 1818 the user into an interactive multimedia session unless the user has 1819 explicitly pre-authorised such action. As it is not always simple to 1820 tell whether or not a session is interactive, applications that are 1821 unsure should assume sessions are interactive. 1823 In this specification, there are no attributes that would allow the 1824 recipient of a session description to be informed to start multimedia 1825 tools in a mode where they default to transmitting. Under some 1826 circumstances it might be appropriate to define such attributes. If 1827 this is done, an application parsing a session description containing 1828 such attributes SHOULD either ignore them or inform the user that 1829 joining this session will result in the automatic transmission of 1830 multimedia data. The default behaviour for an unknown attribute is 1831 to ignore it. 1833 In certain environments, it has become common for intermediary 1834 systems to intercept and analyse session descriptions contained 1835 within other signalling protocols. This is done for a range of 1836 purposes, including but not limited to opening holes in firewalls to 1837 allow media streams to pass, or to mark, prioritize, or block traffic 1838 selectively. In some cases, such intermediary systems may modify the 1839 session description, for example, to have the contents of the session 1840 description match NAT bindings dynamically created. These behaviours 1841 are NOT RECOMMENDED unless the session description is conveyed in 1842 such a manner that allows the intermediary system to conduct proper 1843 checks to establish the authenticity of the session description, and 1844 the authority of its source to establish such communication sessions. 1845 SDP by itself does not include sufficient information to enable these 1846 checks: they depend on the encapsulating protocol (e.g., SIP or 1847 RTSP). 1849 Use of the "k=" line poses a significant security risk, since it 1850 conveys session encryption keys in the clear. SDP MUST NOT be used 1851 to convey key material, unless it can be guaranteed that the channel 1852 over which the SDP is delivered is both private and authenticated. 1853 Moreover, the "k=" line provides no way to indicate or negotiate 1854 cryptographic key algorithms. As it provides for only a single 1855 symmetric key, rather than separate keys for confidentiality and 1856 integrity, its utility is severely limited. The use of the "k=" line 1857 is NOT RECOMMENDED, as discussed in Section 5.12. 1859 8. IANA Considerations 1861 8.1. The "application/sdp" Media Type 1863 One media type registration from [RFC4566] is to be updated, as 1864 defined below. 1866 To: ietf-types@iana.org 1867 Subject: Registration of media type "application/sdp" 1869 Type name: application 1871 Subtype name: sdp 1873 Required parameters: None. 1875 Optional parameters: None. 1877 Encoding considerations: 1878 SDP files are primarily UTF-8 format text. The "a=charset:" 1879 attribute may be used to signal the presence of other character 1880 sets in certain parts of an SDP file (see Section 6 of RFC 1881 XXXX). Arbitrary binary content cannot be directly 1882 represented in SDP. 1884 Security considerations: 1885 See Section 7 of RFC XXXX. 1887 Interoperability considerations: 1888 See RFC XXXX. 1890 Published specification: 1891 See RFC XXXX. 1893 Applications which use this media type: 1894 Voice over IP, video teleconferencing, streaming media, instant 1895 messaging, among others. See also Section 3 of RFC XXXX. 1897 Additional information: 1899 Magic number(s): None. 1900 File extension(s): The extension ".sdp" is commonly used. 1901 Macintosh File Type Code(s): "sdp " 1903 Person & email address to contact for further information: 1904 IETF MMUSIC working group 1906 Intended usage: COMMON 1908 Author/Change controller: 1909 Authors of RFC XXXX 1910 IETF MMUSIC working group delegated from the IESG 1912 8.2. Registration of Parameters 1914 There are seven field names that are registered with IANA. Using the 1915 terminology in the SDP specification Backus-Naur Form (BNF), they are 1916 "media", "proto", "fmt", "att-field", "bwtype", "nettype", and 1917 "addrtype". 1919 The contact address for all parameters registered below is: 1921 IETF MMUSIC working group 1923 8.2.1. Media Types ("media") 1925 The set of media types is intended to be small and SHOULD NOT be 1926 extended except under rare circumstances. The same rules should 1927 apply for media names as for top-level media types, and where 1928 possible the same name should be registered for SDP as for MIME. For 1929 media other than existing top-level media types, a Standards Track 1930 RFC MUST be produced for a new top-level media type to be registered, 1931 and the registration MUST provide good justification why no existing 1932 media name is appropriate (the "Standards Action" policy of 1933 [RFC5226]. 1935 This memo registers the media types "audio", "video", "text", 1936 "application", and "message". 1938 Note: The media types "control" and "data" were listed as valid in an 1939 early version of this specification (RFC 2327); however, their 1940 semantics were never fully specified and they are not widely used. 1941 These media types have been removed in this specification, although 1942 they still remain valid media type capabilities for a SIP user agent 1943 as defined in [RFC3840]. If these media types are considered useful 1944 in the future, a Standards Track RFC MUST be produced to document 1945 their use. Until that is done, applications SHOULD NOT use these 1946 types and SHOULD NOT declare support for them in SIP capabilities 1947 declarations (even though they exist in the registry created by 1948 [RFC3840]). 1950 8.2.2. Transport Protocols ("proto") 1952 The "proto" field describes the transport protocol used. This SHOULD 1953 reference a standards-track protocol RFC. This memo registers three 1954 values: "RTP/AVP" is a reference to [RFC3550] used under the RTP 1955 Profile for Audio and Video Conferences with Minimal Control 1956 [RFC3551] running over UDP/IP, "RTP/SAVP" is a reference to the 1957 Secure Real-time Transport Protocol [RFC3711], and "udp" indicates an 1958 unspecified protocol over UDP. 1960 If other RTP profiles are defined in the future, their "proto" name 1961 SHOULD be specified in the same manner. For example, an RTP profile 1962 whose short name is "XYZ" would be denoted by a "proto" field of 1963 "RTP/XYZ". 1965 New transport protocols SHOULD be registered with IANA. 1966 Registrations MUST reference an RFC describing the protocol. Such an 1967 RFC MAY be Experimental or Informational, although it is preferable 1968 that it be Standards Track. Registrations MUST also define the rules 1969 by which their "fmt" namespace is managed (see below). 1971 8.2.3. Media Formats ("fmt") 1973 Each transport protocol, defined by the "proto" field, has an 1974 associated "fmt" namespace that describes the media formats that may 1975 be conveyed by that protocol. Formats cover all the possible 1976 encodings that could be transported in a multimedia session. 1978 RTP payload formats under the "RTP/AVP" and "RTP/SAVP" profiles MUST 1979 use the payload type number as their "fmt" value. If the payload 1980 type number is dynamically assigned by this session description, an 1981 additional "rtpmap" attribute MUST be included to specify the format 1982 name and parameters as defined by the media type registration for the 1983 payload format. It is RECOMMENDED that other RTP profiles that are 1984 registered (in combination with RTP) as SDP transport protocols 1985 specify the same rules for the "fmt" namespace. 1987 For the "udp" protocol, new formats SHOULD be registered. Use of an 1988 existing media subtype for the format is encouraged. If no media 1989 subtype exists, it is RECOMMENDED that a suitable one be registered 1990 through the IETF process [RFC6838] by production of, or reference to, 1991 a standards-track RFC that defines the transport protocol for the 1992 format. 1994 For other protocols, formats MAY be registered according to the rules 1995 of the associated "proto" specification. 1997 Registrations of new formats MUST specify which transport protocols 1998 they apply to. 2000 8.2.4. Attribute Names ("att-field") 2002 8.2.4.1. New Attributes 2004 Attribute field names ("att-field") MUST be registered with IANA and 2005 documented, because of noticeable issues due to conflicting 2006 attributes under the same name. Unknown attributes in SDP are simply 2007 ignored, but conflicting ones that fragment the protocol are a 2008 serious problem. 2010 New attribute registrations are accepted according to the 2011 "Specification Required" policy of [RFC5226], provided that the 2012 specification includes the following information: 2014 o Contact Name. 2016 o Contact Email Address. 2018 o Attribute Name: The name of the attribute that will appear in 2019 SDP). This MUST conform to the definition of . 2021 o Attribute Syntax: For a value attribute (see clause 5.13), an ABNF 2022 definition of the attribute value syntax (See 2023 Section Section 9) MUST be provided. The syntax MUST follow the 2024 rule form as per Section 2.2 of [RFC5234]. This SHALL define the 2025 allowable values that the attribute might take. It MAY also 2026 define an extension method for the addition of future values. For 2027 a property attribute, the ABNF definition is omitted as the 2028 property attribute takes no values. 2030 o Attribute Semantics: For a value attribute, a semantic description 2031 of the values that the attribute might take MUST be provided. The 2032 usage of a property attribute is described under purpose below. 2034 o Attribute Value: The name of an ABNF syntax rule defining the 2035 syntax of the value. Absence of a rule name indicates that the 2036 attribute takes no values. Enclosing the rule name in "[" and "]" 2037 indicates that a value is optional. 2039 o Usage Level: Usage level(s) of the attribute. One or more of: 2040 session, media, source, dcsa, dcsa(subprotocol). For a definition 2041 of source level attributes, see [RFC5576]. For a definition of 2042 dcsa attributes see: [I-D.ietf-mmusic-data-channel-sdpneg]. 2044 o Charset Dependent: Whether the attribute value is subject to the 2045 charset attribute or not (Yes/No). 2047 o Purpose: An explanation of the purpose and usage of the attribute. 2049 o O/A Procedures: Offer/Answer procedures as explained in [RFC3264]. 2051 o Mux Category: Indication of which multiplexing "category" 2052 [I-D.ietf-mmusic-sdp-mux-attributes] an attribute is associated 2053 with. 2055 o Reference: A reference to the specification defining the 2056 attribute. 2058 The above is the minimum that IANA will accept. Attributes that are 2059 expected to see widespread use and interoperability SHOULD be 2060 documented with a standards-track RFC that specifies the attribute 2061 more precisely. 2063 Submitters of registrations should ensure that the specification is 2064 in the spirit of SDP attributes, most notably that the attribute is 2065 platform independent in the sense that it makes no implicit 2066 assumptions about operating systems and does not name specific pieces 2067 of software in a manner that might inhibit interoperability. 2069 Submitters of registrations should also carefully choose the 2070 attribute usage level. They should not choose only "session" when 2071 the attribute can have different values when media is disaggregated, 2072 i.e., when each m= section has its own IP address on a different 2073 endpoint. In that case the attribute type chosen should be "session, 2074 media". The default rule is that for all new SDP attributes that can 2075 occur both in session and media level, the media level overrides the 2076 session level. When this is not the case for a new SDP attribute, it 2077 MUST be explicitly stated. 2079 IANA has registered the initial set of attribute names ("att-field" 2080 values), with definitions as in Section 6 of this memo (these 2081 definitions replace those in [RFC4566]). 2083 8.2.4.2. Updates to Existing Attributes 2085 Updated attribute registrations are accepted according to the 2086 "Specification Required" policy of [RFC5226], provided that the 2087 specification updating the attribute (for example, by adding a new 2088 value) considers the registration information items from 2089 Section Section 8.2.4.1 according to the following bullets: 2091 o Contact Name: A name MUST be provided. 2093 o Contact Email Address: An email address MUST be provided. 2095 o Attribute Name: MUST be provided and MUST NOT be changed. 2096 Otherwise it is a new attribute. 2098 o Attribute Syntax: The existing rule syntax with the syntax 2099 extensions MUST be provided if there is a change to the syntax. A 2100 revision to an existing attribute usage MAY extend the syntax of 2101 an attribute, but MUST be backward compatible. 2103 o Attribute Semantics: A semantic description of new additional 2104 attributes values or a semantic extension of existing values. 2105 Existing attribute values semantics MUST only be extended in a 2106 backward compatible manner. 2108 o Usage Level: Updates MAY only add additional levels. 2110 o Charset Dependent: MUST NOT be changed. 2112 o Purpose: MAY be extended according to the updated usage. 2114 o O/A Procedures: MAY be updated in a backward compatible manner 2115 and/or it applies to a new usage level only. 2117 o Mux Category: No change unless from TBD to another value. It MAY 2118 also change if 'media' level is being added to the definition of 2119 an attribute that previously did not include it. 2121 o Reference: A new reference MUST be provided. 2123 Items SHOULD be omitted if there is no impact to them as a result of 2124 the attribute update. 2126 8.2.5. Bandwidth Specifiers ("bwtype") 2128 A proliferation of bandwidth specifiers is strongly discouraged. 2130 New bandwidth specifiers ("bwtype" fields) MUST be registered with 2131 IANA. The submission MUST reference a standards-track RFC specifying 2132 the semantics of the bandwidth specifier precisely, and indicating 2133 when it should be used, and why the existing registered bandwidth 2134 specifiers do not suffice. 2136 IANA has registered the bandwidth specifiers "CT" and "AS" with 2137 definitions as in Section 5.8 of this memo (these definitions update 2138 those in [RFC4566]). 2140 8.2.6. Network Types ("nettype") 2142 New network types (the "nettype" field) MUST be registered with IANA 2143 if SDP needs to be used in the context of non-Internet environments. 2144 The registration is subject to the RFC Required - RFC publication 2145 policy of [RFC5226]. Although these are not normally the preserve of 2146 IANA, there may be circumstances when an Internet application needs 2147 to interoperate with a non-Internet application, such as when 2148 gatewaying an Internet telephone call into the Public Switched 2149 Telephone Network (PSTN). The number of network types should be 2150 small and should be rarely extended. A new network type cannot be 2151 registered without registering at least one address type to be used 2152 with that network type. A new network type registration MUST 2153 reference an RFC that gives details of the network type and address 2154 type(s) and specifies how and when they would be used. 2156 IANA has registered the network type "IN" to represent the Internet, 2157 with definition as in Sections 5.2 and 5.7 of this memo (these 2158 definitions update those in [RFC4566]). 2160 8.2.7. Address Types ("addrtype") 2162 New address types ("addrtype") MUST be registered with IANA. The 2163 registration is subject to the RFC Required - RFC publication policy 2164 of [RFC5226]. An address type is only meaningful in the context of a 2165 network type, and any registration of an address type MUST specify a 2166 registered network type or be submitted along with a network type 2167 registration. A new address type registration MUST reference an RFC 2168 giving details of the syntax of the address type. Address types are 2169 not expected to be registered frequently. 2171 IANA has registered the address types "IP4" and "IP6" with 2172 definitions as in Sections 5.2 and 5.7 of this memo (these 2173 definitions update those in [RFC4566]). 2175 8.2.8. Registration Procedure 2177 In the RFC documentation that registers SDP "media", "proto", "fmt", 2178 "bwtype", "nettype", and "addrtype" fields, the authors MUST include 2179 the following information for IANA to place in the appropriate 2180 registry: 2182 o contact name, email address, and telephone number 2184 o name being registered (as it will appear in SDP) 2186 o long-form name in English 2188 o type of name ("media", "proto", "fmt", "bwtype", "nettype", or 2189 "addrtype") 2191 o a one-paragraph explanation of the purpose of the registered name 2193 o a reference to the specification for the registered name (this 2194 will typically be an RFC number) 2196 In the case of a new addrtype registration, the author has to check 2197 whether the new address type is usable with the existing network 2198 types. If yes, the "nettype" registry MUST be updated accordingly. 2200 In the case of a new nettype registration, the author MUST specify 2201 the usable address type(s). 2203 IANA may refer any registration to the IESG for review, and may 2204 request revisions to be made before a registration will be made. 2206 8.3. Encryption Key Access Methods 2208 The IANA previously maintained a table of SDP encryption key access 2209 method ("enckey") names. This table is obsolete, since the "k=" line 2210 is not extensible. New registrations MUST NOT be accepted. 2212 8.4. Reorganization of the nettype Registry 2214 This document adds a new column in the "nettype" registry with the 2215 title "Usable addrtype Values" and updates the "nettype" registry as 2216 follows: 2218 -------------------------------------------------------------------- 2219 |Type | SDP Name | Usable addrtype Values | Reference | 2220 -------------------------------------------------------------------- 2221 |nettype | IN | IP4, IP6 | [RFC4566] | 2222 |nettype | TN | RFC2543 | [RFC2848] | 2223 |nettype | ATM | NSAP, GWID, E164 | [RFC3108] | 2224 |nettype | PSTN | E164 | [RFC7195] | 2225 -------------------------------------------------------------------- 2227 Note that both [RFC7195] and [RFC3108] registered "E164" as an 2228 address type, although [RFC7195] mentions that the "E164" address 2229 type has a different context for ATM and PSTN networks. 2231 8.5. Reorganization of the att-field Registries 2233 This document combines all of the (currently) five "att-field" 2234 registries into one registry called "att-field" registry, and updates 2235 the columns to reflect the name, usage level(s), charset dependency 2236 and reference. As such IANA is requested to create a new combined 2237 registry using the following columns: 2239 Name | Usage Level | Dependent on Charset? | Mux Category | Reference 2241 The "Name" column reflects the attribute name (as it will appear in 2242 the SDP). The "Usage Level" column MUST indicate one or more of the 2243 following: session, media, source, dcsa and dcsa(subprotocol). The 2244 "Dependent on Charset?" column MUST indicate "Yes" or "No" depending 2245 on whether the attribute value is subject to the charset attribute. 2246 The "Mux Category" column MUST indicate one of the following 2247 categories: NORMAL, NOT RECOMMENDED, IDENTICAL, SUM, TRANSPORT, 2248 INHERIT, IDENTICAL-PER-PT, SPECIAL or TBD as defined by 2249 [I-D.ietf-mmusic-sdp-mux-attributes]. Finally, the "Reference" 2250 column indicates the specification(s) where the attribute is defined. 2252 For example, the attribute "setup" which is defined for both session 2253 and media level, will be listed in the new registry as follows: 2255 Name | Usage Level | Dependent on Charset? | Mux Category | Reference 2256 setup | session,media, | No | IDENTICAL | [RFC4145],[RFC6135], | 2257 | dcsa,dcsa(msrp)| | | [I-D.mmusic-msrp-usage-data-channel] | 2259 9. SDP Grammar 2261 This section provides an Augmented BNF grammar for SDP. ABNF is 2262 defined in [RFC5234] and [RFC7405]. 2264 ; SDP Syntax 2265 session-description = proto-version 2266 origin-field 2267 session-name-field 2268 information-field 2269 uri-field 2270 email-fields 2271 phone-fields 2272 connection-field 2273 bandwidth-fields 2274 time-fields 2275 key-field 2276 attribute-fields 2277 media-descriptions 2279 proto-version = %s"v" "=" 1*DIGIT CRLF 2280 ;this memo describes version 0 2282 origin-field = %s"o" "=" username SP sess-id SP sess-version SP 2283 nettype SP addrtype SP unicast-address CRLF 2285 session-name-field = %s"s" "=" text CRLF 2287 information-field = [%s"i" "=" text CRLF] 2289 uri-field = [%s"u" "=" uri CRLF] 2291 email-fields = *(%s"e" "=" email-address CRLF) 2293 phone-fields = *(%s"p" "=" phone-number CRLF) 2295 connection-field = [%s"c" "=" nettype SP addrtype SP 2296 connection-address CRLF] 2297 ;a connection field must be present 2298 ;in every media description or at the 2299 ;session-level 2301 bandwidth-fields = *(%s"b" "=" bwtype ":" bandwidth CRLF) 2303 time-fields = 1*( %s"t" "=" start-time SP stop-time 2304 *(CRLF repeat-fields) CRLF) 2305 [zone-adjustments CRLF] 2307 repeat-fields = %s"r" "=" repeat-interval SP typed-time 2308 1*(SP typed-time) 2310 zone-adjustments = %s"z" "=" time SP ["-"] typed-time 2311 *(SP time SP ["-"] typed-time) 2313 key-field = [%s"k" "=" key-type CRLF] 2315 attribute-fields = *(%s"a" "=" attribute CRLF) 2317 media-descriptions = *( media-field 2318 information-field 2319 *connection-field 2320 bandwidth-fields 2321 key-field 2322 attribute-fields ) 2324 media-field = %s"m" "=" media SP port ["/" integer] 2325 SP proto 1*(SP fmt) CRLF 2327 ; sub-rules of 'o=' 2328 username = non-ws-string 2329 ;pretty wide definition, but doesn't 2330 ;include space 2332 sess-id = 1*DIGIT 2333 ;should be unique for this username/host 2335 sess-version = 1*DIGIT 2337 nettype = token 2338 ;typically "IN" 2340 addrtype = token 2341 ;typically "IP4" or "IP6" 2343 ; sub-rules of 'u=' 2344 uri = URI-reference 2345 ; see RFC 3986 2347 ; sub-rules of 'e=', see RFC 5322 for definitions 2348 email-address = address-and-comment / dispname-and-address 2349 / addr-spec 2350 address-and-comment = addr-spec 1*SP "(" 1*email-safe ")" 2351 dispname-and-address = 1*email-safe 1*SP "<" addr-spec ">" 2353 ; sub-rules of 'p=' 2354 phone-number = phone *SP "(" 1*email-safe ")" / 2355 1*email-safe "<" phone ">" / 2356 phone 2358 phone = ["+"] DIGIT 1*(SP / "-" / DIGIT) 2360 ; sub-rules of 'c=' 2361 connection-address = multicast-address / unicast-address 2363 ; sub-rules of 'b=' 2364 bwtype = token 2366 bandwidth = 1*DIGIT 2368 ; sub-rules of 't=' 2369 start-time = time / "0" 2371 stop-time = time / "0" 2373 time = POS-DIGIT 9*DIGIT 2374 ; Decimal representation of NTP time in 2375 ; seconds since 1900. The representation 2376 ; of NTP time is an unbounded length field 2377 ; containing at least 10 digits. Unlike the 2378 ; 64-bit representation used elsewhere, time 2379 ; in SDP does not wrap in the year 2036. 2381 ; sub-rules of 'r=' and 'z=' 2382 repeat-interval = POS-DIGIT *DIGIT [fixed-len-time-unit] 2384 typed-time = 1*DIGIT [fixed-len-time-unit] 2386 fixed-len-time-unit = %s"d" / %s"h" / %s"m" / %s"s" 2387 ; NOTE: These units are case-sensitive. 2389 ; sub-rules of 'k=' 2390 key-type = %s"prompt" 2391 %s"clear:" 2392 %s"base64:" 2393 %s"uri:" 2394 ; NOTE: These names are case-sensitive. 2396 base64 = *base64-unit [base64-pad] 2397 base64-unit = 4base64-char 2398 base64-pad = 2base64-char "==" / 3base64-char "=" 2399 base64-char = ALPHA / DIGIT / "+" / "/" 2401 ; sub-rules of 'a=' 2402 attribute = (att-field ":" att-value) / att-field 2404 att-field = token 2406 att-value = byte-string 2408 ; sub-rules of 'm=' 2409 media = token 2410 ;typically "audio", "video", "text", "image" 2411 ;or "application" 2413 fmt = token 2414 ;typically an RTP payload type for audio 2415 ;and video media 2417 proto = token *("/" token) 2418 ;typically "RTP/AVP" or "udp" 2420 port = 1*DIGIT 2422 ; generic sub-rules: addressing 2423 unicast-address = IP4-address / IP6-address / FQDN / extn-addr 2425 multicast-address = IP4-multicast / IP6-multicast / FQDN 2426 / extn-addr 2428 IP4-multicast = m1 3( "." decimal-uchar ) 2429 "/" ttl [ "/" integer ] 2430 ; IP4 multicast addresses may be in the 2431 ; range 224.0.0.0 to 239.255.255.255 2433 m1 = ("22" ("4"/"5"/"6"/"7"/"8"/"9")) / 2434 ("23" DIGIT ) 2436 IP6-multicast = IP6-address [ "/" integer ] 2437 ; IP6 address starting with FF 2439 ttl = (POS-DIGIT *2DIGIT) / "0" 2440 FQDN = 4*(alpha-numeric / "-" / ".") 2441 ; fully qualified domain name as specified 2442 ; in RFC 1035 (and updates) 2444 IP4-address = b1 3("." decimal-uchar) 2446 b1 = decimal-uchar 2447 ; less than "224" 2449 IP6-address = 6( h16 ":" ) ls32 2450 / "::" 5( h16 ":" ) ls32 2451 / [ h16 ] "::" 4( h16 ":" ) ls32 2452 / [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32 2453 / [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32 2454 / [ *3( h16 ":" ) h16 ] "::" h16 ":" ls32 2455 / [ *4( h16 ":" ) h16 ] "::" ls32 2456 / [ *5( h16 ":" ) h16 ] "::" h16 2457 / [ *6( h16 ":" ) h16 ] "::" 2459 h16 = 1*4HEXDIG 2461 ls32 = ( h16 ":" h16 ) / IP4-address 2463 ; Generic for other address families 2464 extn-addr = non-ws-string 2466 ; generic sub-rules: datatypes 2467 text = byte-string 2468 ;default is to interpret this as UTF8 text. 2469 ;ISO 8859-1 requires "a=charset:ISO-8859-1" 2470 ;session-level attribute to be used 2472 byte-string = 1*(%x01-09/%x0B-0C/%x0E-FF) 2473 ;any byte except NUL, CR, or LF 2475 non-ws-string = 1*(VCHAR/%x80-FF) 2476 ;string of visible characters 2478 token-char = ALPHA / DIGIT 2479 / "!" / "#" / "$" / "%" / "&" 2480 / "'" ; (single quote) 2481 / "*" / "+" / "-" / "." / "^" / "_" 2482 / "`" ; (Grave accent) 2483 / "{" / "|" / "}" / "~" 2485 token = 1*(token-char) 2487 email-safe = %x01-09/%x0B-0C/%x0E-27/%x2A-3B/%x3D/%x3F-FF 2488 ;any byte except NUL, CR, LF, or the quoting 2489 ;characters ()<> 2491 integer = POS-DIGIT *DIGIT 2493 zero-based-integer = "0" / integer 2495 non-zero-int-or-real = integer / non-zero-real 2497 non-zero-real = zero-based-integer "." *DIGIT POS-DIGIT 2499 ; generic sub-rules: primitives 2500 alpha-numeric = ALPHA / DIGIT 2502 POS-DIGIT = %x31-39 ; 1 - 9 2504 decimal-uchar = DIGIT 2505 / POS-DIGIT DIGIT 2506 / ("1" 2*(DIGIT)) 2507 / ("2" ("0"/"1"/"2"/"3"/"4") DIGIT) 2508 / ("2" "5" ("0"/"1"/"2"/"3"/"4"/"5")) 2510 ; external references: 2511 ; ALPHA, DIGIT, CRLF, SP, VCHAR: from RFC 5234 2512 ; URI-reference: from RFC 3986 2513 ; addr-spec: from RFC 5322 2515 10. Summary of Changes from RFC 4566 2517 The ABNF rule for IP6-address has been corrected. As a result, the 2518 ABNF rule for IP6-multicast has changed, and the (now unused) rules 2519 for hexpart, hexseq, and hex4 have been removed. 2521 IP4 unicast and multicast addresses in the example SDP descriptions 2522 have been revised per RFCs 5735 and 5771. 2524 Text in Section 5.2 has been revised to clarify the use of local 2525 addresses in case of ICE-like SDP extensions. 2527 Normative and informative references have been updated. 2529 The text regarding the session vs. media-level attribute usage has 2530 been clarified. 2532 The case-insensitivity rules from RFC 4855 have been included in this 2533 document. 2535 11. Acknowledgements 2537 Many people in the IETF Multiparty Multimedia Session Control 2538 (MMUSIC) working group have made comments and suggestions 2539 contributing to this document. 2541 12. References 2543 12.1. Normative References 2545 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 2546 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 2547 . 2549 [RFC1035] Mockapetris, P., "Domain names - implementation and 2550 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 2551 November 1987, . 2553 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2554 Requirement Levels", BCP 14, RFC 2119, 2555 DOI 10.17487/RFC2119, March 1997, 2556 . 2558 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 2559 Specifications: ABNF", STD 68, RFC 5234, 2560 DOI 10.17487/RFC5234, January 2008, 2561 . 2563 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 2564 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 2565 2003, . 2567 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 2568 Resource Identifier (URI): Generic Syntax", STD 66, 2569 RFC 3986, DOI 10.17487/RFC3986, January 2005, 2570 . 2572 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 2573 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 2574 DOI 10.17487/RFC5226, May 2008, 2575 . 2577 [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying 2578 Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, 2579 September 2009, . 2581 [RFC5890] Klensin, J., "Internationalized Domain Names for 2582 Applications (IDNA): Definitions and Document Framework", 2583 RFC 5890, DOI 10.17487/RFC5890, August 2010, 2584 . 2586 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 2587 Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, 2588 . 2590 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 2591 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 2592 July 2006, . 2594 [RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and 2595 B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms 2596 for Real-Time Transport Protocol (RTP) Sources", RFC 7656, 2597 DOI 10.17487/RFC7656, November 2015, 2598 . 2600 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 2601 Media Attributes in the Session Description Protocol 2602 (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009, 2603 . 2605 [I-D.iana-charset-reg-procedure] 2606 McFadden, M. and A. Melnikov, "IANA Charset Registration 2607 Procedures", draft-iana-charset-reg-procedure-01 (work in 2608 progress), April 2015. 2610 [I-D.ietf-mmusic-sdp-mux-attributes] 2611 Nandakumar, S., "A Framework for SDP Attributes when 2612 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-16 2613 (work in progress), December 2016. 2615 [I-D.ietf-mmusic-data-channel-sdpneg] 2616 Drage, K., Makaraju, M., Stoetzer-Bradler, J., Ejzak, R., 2617 and J. Marcon, "SDP-based Data Channel Negotiation", 2618 draft-ietf-mmusic-data-channel-sdpneg-11 (work in 2619 progress), January 2017. 2621 12.2. Informative References 2623 [RFC2327] Handley, M. and V. Jacobson, "SDP: Session Description 2624 Protocol", RFC 2327, DOI 10.17487/RFC2327, April 1998, 2625 . 2627 [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, 2628 "Network Time Protocol Version 4: Protocol and Algorithms 2629 Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010, 2630 . 2632 [RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session 2633 Announcement Protocol", RFC 2974, DOI 10.17487/RFC2974, 2634 October 2000, . 2636 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 2637 A., Peterson, J., Sparks, R., Handley, M., and E. 2638 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 2639 DOI 10.17487/RFC3261, June 2002, 2640 . 2642 [RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time 2643 Streaming Protocol (RTSP)", RFC 2326, 2644 DOI 10.17487/RFC2326, April 1998, 2645 . 2647 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 2648 with Session Description Protocol (SDP)", RFC 3264, 2649 DOI 10.17487/RFC3264, June 2002, 2650 . 2652 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 2653 Protocol (SDP) Grouping Framework", RFC 5888, 2654 DOI 10.17487/RFC5888, June 2010, 2655 . 2657 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 2658 Jacobson, "RTP: A Transport Protocol for Real-Time 2659 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 2660 July 2003, . 2662 [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and 2663 Video Conferences with Minimal Control", STD 65, RFC 3551, 2664 DOI 10.17487/RFC3551, July 2003, 2665 . 2667 [RFC3556] Casner, S., "Session Description Protocol (SDP) Bandwidth 2668 Modifiers for RTP Control Protocol (RTCP) Bandwidth", 2669 RFC 3556, DOI 10.17487/RFC3556, July 2003, 2670 . 2672 [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute 2673 in Session Description Protocol (SDP)", RFC 3605, 2674 DOI 10.17487/RFC3605, October 2003, 2675 . 2677 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 2678 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 2679 RFC 3711, DOI 10.17487/RFC3711, March 2004, 2680 . 2682 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 2683 "Indicating User Agent Capabilities in the Session 2684 Initiation Protocol (SIP)", RFC 3840, 2685 DOI 10.17487/RFC3840, August 2004, 2686 . 2688 [RFC3890] Westerlund, M., "A Transport Independent Bandwidth 2689 Modifier for the Session Description Protocol (SDP)", 2690 RFC 3890, DOI 10.17487/RFC3890, September 2004, 2691 . 2693 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 2694 (ICE): A Protocol for Network Address Translator (NAT) 2695 Traversal for Offer/Answer Protocols", RFC 5245, 2696 DOI 10.17487/RFC5245, April 2010, 2697 . 2699 [RFC6544] Rosenberg, J., Keranen, A., Lowekamp, B., and A. Roach, 2700 "TCP Candidates with Interactive Connectivity 2701 Establishment (ICE)", RFC 6544, DOI 10.17487/RFC6544, 2702 March 2012, . 2704 [RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF", 2705 RFC 7405, DOI 10.17487/RFC7405, December 2014, 2706 . 2708 [ITU.H332.1998] 2709 International Telecommunication Union, "H.323 extended for 2710 loosely coupled conferences", ITU Recommendation H.332, 2711 September 1998. 2713 [RFC4567] Arkko, J., Lindholm, F., Naslund, M., Norrman, K., and E. 2714 Carrara, "Key Management Extensions for Session 2715 Description Protocol (SDP) and Real Time Streaming 2716 Protocol (RTSP)", RFC 4567, DOI 10.17487/RFC4567, July 2717 2006, . 2719 [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session 2720 Description Protocol (SDP) Security Descriptions for Media 2721 Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006, 2722 . 2724 [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, 2725 DOI 10.17487/RFC5322, October 2008, 2726 . 2728 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type 2729 Specifications and Registration Procedures", BCP 13, 2730 RFC 6838, DOI 10.17487/RFC6838, January 2013, 2731 . 2733 [RFC4855] Casner, S., "Media Type Registration of RTP Payload 2734 Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007, 2735 . 2737 Authors' Addresses 2739 Mark Handley 2740 University College London 2741 Department of Computer Science 2742 London WC1E 6BT 2743 UK 2745 EMail: M.Handley@cs.ucl.ac.uk 2747 Van Jacobson 2748 PARC 2749 3333 Coyote Hill Road 2750 Palo Alto, CA 94304 2751 USA 2753 EMail: van@parc.com 2755 Colin Perkins 2756 University of Glasgow 2757 School of Computing Science 2758 University of Glasgow 2759 Glasgow G12 8QQ 2760 UK 2762 EMail: csp@csperkins.org 2763 Ali Begen 2764 Networked Media 2765 Konya 2766 Turkey 2768 EMail: ali.begen@networked.media