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'10') (Obsoleted by RFC 4646, RFC 4647) ** Obsolete normative reference: RFC 3490 (ref. '11') (Obsoleted by RFC 5890, RFC 5891) ** Obsolete normative reference: RFC 3548 (ref. '12') (Obsoleted by RFC 4648) -- Obsolete informational reference (is this intentional?): RFC 1305 (ref. '13') (Obsoleted by RFC 5905) -- Obsolete informational reference (is this intentional?): RFC 2326 (ref. '16') (Obsoleted by RFC 7826) == Outdated reference: A later version (-15) exists of draft-ietf-mmusic-kmgmt-ext-12 == Outdated reference: A later version (-12) exists of draft-ietf-mmusic-sdescriptions-07 Summary: 12 errors (**), 0 flaws (~~), 9 warnings (==), 11 comments (--).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: 2327, 3266 (if V. Jacobson 5 approved) Packet Design 6 Expires: January 17, 2006 C. Perkins 7 University of Glasgow 8 July 16, 2005 10 SDP: Session Description Protocol 11 draft-ietf-mmusic-sdp-new-25.txt 13 Status of this Memo 15 By submitting this Internet-Draft, each author represents that any 16 applicable patent or other IPR claims of which he or she is aware 17 have been or will be disclosed, and any of which he or she becomes 18 aware will be disclosed, in accordance with Section 6 of BCP 79. 20 Internet-Drafts are working documents of the Internet Engineering 21 Task Force (IETF), its areas, and its working groups. Note that 22 other groups may also distribute working documents as Internet- 23 Drafts. 25 Internet-Drafts are draft documents valid for a maximum of six months 26 and may be updated, replaced, or obsoleted by other documents at any 27 time. It is inappropriate to use Internet-Drafts as reference 28 material or to cite them other than as "work in progress." 30 The list of current Internet-Drafts can be accessed at 31 http://www.ietf.org/ietf/1id-abstracts.txt. 33 The list of Internet-Draft Shadow Directories can be accessed at 34 http://www.ietf.org/shadow.html. 36 This Internet-Draft will expire on January 17, 2006. 38 Copyright Notice 40 Copyright (C) The Internet Society (2005). 42 Abstract 44 This memo defines the Session Description Protocol (SDP). SDP is 45 intended for describing multimedia sessions for the purposes of 46 session announcement, session invitation, and other forms of 47 multimedia session initiation. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 52 2. Glossary of Terms . . . . . . . . . . . . . . . . . . . . . 3 53 3. Examples of SDP Usage . . . . . . . . . . . . . . . . . . . 4 54 3.1 Multicast Session Announcement . . . . . . . . . . . . . . 4 55 3.2 Session Initiation . . . . . . . . . . . . . . . . . . . . 4 56 3.3 Streaming media . . . . . . . . . . . . . . . . . . . . . 4 57 3.4 Email and the World Wide Web . . . . . . . . . . . . . . . 4 58 4. Requirements and Recommendations . . . . . . . . . . . . . . 5 59 4.1 Media and Transport Information . . . . . . . . . . . . . 6 60 4.2 Timing Information . . . . . . . . . . . . . . . . . . . . 6 61 4.3 Private Sessions . . . . . . . . . . . . . . . . . . . . . 7 62 4.4 Obtaining Further Information about a Session . . . . . . 7 63 4.5 Categorisation . . . . . . . . . . . . . . . . . . . . . . 7 64 4.6 Internationalisation . . . . . . . . . . . . . . . . . . . 7 65 5. SDP Specification . . . . . . . . . . . . . . . . . . . . . 7 66 5.1 Protocol Version ("v=") . . . . . . . . . . . . . . . . . 10 67 5.2 Origin ("o=") . . . . . . . . . . . . . . . . . . . . . . 10 68 5.3 Session Name ("s=") . . . . . . . . . . . . . . . . . . . 12 69 5.4 Session Information ("i=") . . . . . . . . . . . . . . . . 12 70 5.5 URI ("u=") . . . . . . . . . . . . . . . . . . . . . . . . 12 71 5.6 Email Address and Phone Number ("e=" and "p=") . . . . . . 13 72 5.7 Connection Data ("c=") . . . . . . . . . . . . . . . . . . 13 73 5.8 Bandwidth ("b=") . . . . . . . . . . . . . . . . . . . . . 15 74 5.9 Timing ("t=") . . . . . . . . . . . . . . . . . . . . . . 16 75 5.10 Repeat Times ("r=") . . . . . . . . . . . . . . . . . . 17 76 5.11 Time Zones ("z=") . . . . . . . . . . . . . . . . . . . 18 77 5.12 Encryption Keys ("k=") . . . . . . . . . . . . . . . . . 19 78 5.13 Attributes ("a=") . . . . . . . . . . . . . . . . . . . 21 79 5.14 Media Descriptions ("m=") . . . . . . . . . . . . . . . 22 80 6. SDP Attributes . . . . . . . . . . . . . . . . . . . . . . . 25 81 7. Security Considerations . . . . . . . . . . . . . . . . . . 31 82 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . 32 83 8.1 The "application/sdp" media type . . . . . . . . . . . . . 32 84 8.2 Registration of Parameters . . . . . . . . . . . . . . . . 34 85 8.3 Encryption Key Access Methods . . . . . . . . . . . . . . 38 86 9. SDP Grammar . . . . . . . . . . . . . . . . . . . . . . . . 39 87 10. Summary of Changes from RFC 2327 . . . . . . . . . . . . . . 44 88 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 44 89 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 45 90 12.1 Normative References . . . . . . . . . . . . . . . . . . 45 91 12.2 Informative References . . . . . . . . . . . . . . . . . 46 92 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 47 93 Intellectual Property and Copyright Statements . . . . . . . 48 95 1. Introduction 97 When initiating multimedia teleconferences, voice-over-IP calls, 98 streaming video, or other sessions, there is a requirement to convey 99 media details, transport addresses, and other session description 100 metadata to the participants. 102 SDP provides a standard representation for such information, 103 irrespective of how that information is transported. SDP is purely a 104 format for session description - it does not incorporate a transport 105 protocol, and is intended to use different transport protocols as 106 appropriate, including the Session Announcement Protocol [14], 107 Session Initiation Protocol [15], Real-Time Streaming Protocol [16], 108 electronic mail using the MIME extensions, and the Hypertext 109 Transport Protocol. 111 SDP is intended to be general purpose so that it can be used in a 112 wide range of network environments and applications. However, it is 113 not intended to support negotiation of session content or media 114 encodings: this is viewed as outside the scope of session 115 description. 117 This memo updates RFC 2327 [6] in the light of implementation 118 experience, and adds a small number of new features. Section 10 119 outlines the changes introduced in this memo. 121 2. Glossary of Terms 123 The following terms are used in this document, and have specific 124 meaning within the context of this document. 126 Conference: A multimedia conference is a set of two or more 127 communicating users along with the software they are using to 128 communicate. 130 Session: A multimedia session is a set of multimedia senders and 131 receivers and the data streams flowing from senders to receivers. 132 A multimedia conference is an example of a multimedia session. 134 Session Description: A well defined format for conveying sufficient 135 information to discover and participate in a multimedia session. 137 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 138 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 139 document are to be interpreted as described in RFC 2119 [3]. 141 3. Examples of SDP Usage 143 3.1 Multicast Session Announcement 145 In order to assist the advertisement of multicast multimedia 146 conferences and other multicast sessions, and to communicate the 147 relevant session setup information to prospective participants, a 148 distributed session directory may be used. An instance of such a 149 session directory periodically sends packets containing a description 150 of the session to a well known multicast group. These advertisements 151 are received by other session directories such that potential remote 152 participants can use the session description to start the tools 153 required to participate in the session. 155 One protocol commonly used to implement such a distributed directory 156 is the Session Announcement Protocol, SAP [14]. SDP provides the 157 recommended session description format for such session 158 announcements. 160 3.2 Session Initiation 162 The Session Initiation Protocol, SIP [15] is an application layer 163 control protocol for creating, modifying and terminating sessions 164 such as Internet multimedia conferences, Internet telephone calls and 165 multimedia distribution. The SIP messages used to create sessions 166 carry session descriptions which allow participants to agree on a set 167 of compatible media types. These session descriptions are commonly 168 formatted using SDP. When used with SIP, the offer/answer model [17] 169 provides a limited framework for negotiation using SDP. 171 3.3 Streaming media 173 The Real Time Streaming Protocol, RTSP [16], is an application-level 174 protocol for control over the delivery of data with real-time 175 properties. RTSP provides an extensible framework to enable 176 controlled, on-demand delivery of real-time data, such as audio and 177 video. An RTSP client and server negotiate an appropriate set of 178 parameters for media delivery, partially using SDP syntax to describe 179 those parameters. 181 3.4 Email and the World Wide Web 183 Alternative means of conveying session descriptions include 184 electronic mail and the World Wide Web. For both email and WWW 185 distribution, the MIME content type "application/sdp" is used. This 186 enables the automatic launching of applications for participation in 187 the session from the WWW client or mail reader in a standard manner. 189 Note that announcements of multicast sessions made only via email or 190 the World Wide Web (WWW) do not have the property that the receiver 191 of a session announcement can necessarily receive the session because 192 the multicast sessions may be restricted in scope, and access to the 193 WWW server or reception of email is possible outside this scope. 194 Session announcements made using SAP do not suffer this mismatch. 196 4. Requirements and Recommendations 198 The purpose of SDP is to convey information about media streams in 199 multimedia sessions to allow the recipients of a session description 200 to participate in the session. SDP is primarily intended for use in 201 an internetwork, although it is sufficiently general that it can 202 describe conferences in other network environments. Media streams 203 can be many-to-many. The times during which the session is active 204 need not be continuous. 206 Thus far, multicast based sessions on the Internet have differed from 207 many other forms of conferencing in that anyone receiving the traffic 208 can join the session (unless the session traffic is encrypted). In 209 such an environment, SDP serves two primary purposes. It is a means 210 to communicate the existence of a session, and is a means to convey 211 sufficient information to enable joining and participating in the 212 session. In a unicast environment, only the latter purpose is likely 213 to be relevant. 215 An SDP session description includes: 217 o Session name and purpose 219 o Time(s) the session is active 221 o The media comprising the session 223 o Information needed to receive those media (addresses, ports, 224 formats and so on) 226 As resources necessary to participate in a session may be limited, 227 some additional information may also be desirable: 229 o Information about the bandwidth to be used by the session 231 o Contact information for the person responsible for the session 233 In general, SDP must convey sufficient information to enable 234 applications to join a session (with the possible exception of 235 encryption keys), and to announce the resources to be used to any 236 non-participants that may need to know (this latter feature is 237 primarily useful when SDP is used with a multicast session 238 announcement protocol). 240 4.1 Media and Transport Information 242 An SDP session description includes the following media information: 244 o The type of media (video, audio, etc.) 246 o The transport protocol (RTP/UDP/IP, H.320, etc.) 248 o The format of the media (H.261 video, MPEG video, etc.) 250 In addition to media format and transport protocol, SDP conveys 251 address and port details. For an IP multicast session, these 252 comprise: 254 o The multicast group address for media 256 o The transport port for media 258 This address and port are the destination address and destination 259 port of the multicast stream, whether being sent, received, or both. 261 For unicast IP sessions, the following are conveyed: 263 o The remote address for media 265 o The remote transport port for media 267 The semantics of this address and port depend on the media and 268 transport protocol defined. By default, this SHOULD be the remote 269 address and remote port to which data is sent. Some media types MAY 270 redefine this behaviour, but this is NOT RECOMMENDED. 272 4.2 Timing Information 274 Sessions may either be bounded or unbounded in time. Whether or not 275 they are bounded, they may be only active at specific times. SDP can 276 convey: 278 o An arbitrary list of start and stop times bounding the session 280 o For each bound, repeat times such as "every Wednesday at 10am for 281 one hour" 283 This timing information is globally consistent, irrespective of local 284 time zone or daylight saving time. 286 4.3 Private Sessions 288 It is possible to create both public sessions and private sessions. 289 SDP itself does not distinguish between these: private sessions are 290 typically conveyed by encrypting the session description during 291 distribution. The details of how encryption is performed are 292 dependent on the mechanism used to convey SDP: mechanisms are 293 currently defined for SDP transported using SAP [14] and SIP [15], 294 others may be defined in future. 296 If a session announcement is private it is possible to use that 297 private announcement to convey encryption keys necessary to decode 298 each of the media in a conference, including enough information to 299 know which encryption scheme is used for each media. 301 4.4 Obtaining Further Information about a Session 303 A session description should convey enough information to decide 304 whether or not to participate in a session. SDP may include 305 additional pointers in the form of Universal Resources Identifiers 306 (URIs) for more information about the session. 308 4.5 Categorisation 310 When many session descriptions are being distributed by SAP, or any 311 other advertisement mechanism, it may be desirable to filter session 312 announcements that are of interest from those that are not. SDP 313 supports a categorisation mechanism for sessions that is capable of 314 being automated. 316 4.6 Internationalisation 318 The SDP specification recommends the use of the ISO 10646 character 319 sets in the UTF-8 encoding [5] to allow many different languages to 320 be represented. However, to assist in compact representations, SDP 321 also allows other character sets such as ISO 8859-1 to be used when 322 desired. Internationalisation only applies to free-text fields 323 (session name and background information), and not to SDP as a whole. 325 5. SDP Specification 327 An SDP session description is denoted by the MIME content type 328 "application/sdp" (See Section 8). 330 An SDP session description is entirely textual using the ISO 10646 331 character set in UTF-8 encoding. SDP field names and attribute names 332 use only the US-ASCII subset of UTF-8, but textual fields and 333 attribute values MAY use the full ISO 10646 character set. Field and 334 attribute values which use the full UTF-8 character set are never 335 directly compared, hence there is no requirement for UTF-8 336 normalisation. The textual form, as opposed to a binary encoding 337 such as ASN.1 or XDR, was chosen to enhance portability, to enable a 338 variety of transports to be used, and to allow flexible, text-based 339 toolkits to be used to generate and process session descriptions. 340 However, since SDP may be used in environments where the maximum 341 permissible size of a session description is limited, the encoding is 342 deliberately compact. Also, since announcements may be transported 343 via very unreliable means or damaged by an intermediate caching 344 server, the encoding was designed with strict order and formatting 345 rules so that most errors would result in malformed session 346 announcements which could be detected easily and discarded. This 347 also allows rapid discarding of encrypted session announcements for 348 which a receiver does not have the correct key. 350 An SDP session description consists of a number of lines of text of 351 the form: 353 = 355 where MUST be exactly one case-significant character and 356 is structured text whose format depends on . In 357 general is either a number of fields delimited by a single 358 space character, or a free format string. Whitespace MUST NOT be 359 used either side of the "=" sign. 361 An SDP session description consists of a session-level section 362 followed by zero or more media-level sections. The session-level 363 part starts with a "v=" line and continues to the first media-level 364 section. The media description starts with an "m=" line and 365 continues to the next media description or end of the whole session 366 description. In general, session-level values are the default for 367 all media unless overridden by an equivalent media-level value. 369 Some lines in each description are REQUIRED and some are OPTIONAL but 370 all MUST appear in exactly the order given here (the fixed order 371 greatly enhances error detection and allows for a simple parser). 372 OPTIONAL items are marked with a "*". 374 Session description 375 v= (protocol version) 376 o= (owner/creator and session identifier) 377 s= (session name) 378 i=* (session information) 379 u=* (URI of description) 380 e=* (email address) 381 p=* (phone number) 382 c=* (connection information - not required if included in 383 all media) 384 b=* (zero or more bandwidth information lines) 385 One or more time descriptions ("t=" and "r=" lines, see below) 386 z=* (time zone adjustments) 387 k=* (encryption key) 388 a=* (zero or more session attribute lines) 389 Zero or more media descriptions 391 Time description 392 t= (time the session is active) 393 r=* (zero or more repeat times) 395 Media description, if present 396 m= (media name and transport address) 397 i=* (media title) 398 c=* (connection information - optional if included at 399 session-level) 400 b=* (zero or more bandwidth information lines) 401 k=* (encryption key) 402 a=* (zero or more media attribute lines) 404 The set of type letters is deliberately small and not intended to be 405 extensible -- an SDP parser MUST completely ignore any session 406 description that contains a type letter that it does not understand. 407 The attribute mechanism ("a=" described below) is the primary means 408 for extending SDP and tailoring it to particular applications or 409 media. Some attributes (the ones listed in Section 6 of this memo) 410 have a defined meaning, but others may be added on an application-, 411 media- or session-specific basis. An SDP parser MUST ignore any 412 attribute it doesn't understand. 414 An SDP session description may contain URIs which reference external 415 content in the "u=", "k=" and "a=" lines. These URIs may be 416 dereferenced in some cases, making the session description non-self 417 contained. 419 The connection ("c=") and attribute ("a=") information in the 420 session-level section applies to all the media of that session unless 421 overridden by connection information or an attribute of the same name 422 in the media description. For instance, in the example below, each 423 media behaves as if it were given a "recvonly" attribute. 425 An example SDP description is: 427 v=0 428 o=jdoe 2890844526 2890842807 IN IP4 10.47.16.5 429 s=SDP Seminar 430 i=A Seminar on the session description protocol 431 u=http://www.example.com/seminars/sdp.pdf 432 e=j.doe@example.com (Jane Doe) 433 c=IN IP4 224.2.17.12/127 434 t=2873397496 2873404696 435 a=recvonly 436 m=audio 49170 RTP/AVP 0 437 m=video 51372 RTP/AVP 99 438 a=rtpmap:99 h263-1998/90000 440 Text fields such as the session name and information are octet 441 strings which may contain any octet with the exceptions of 0x00 442 (Nul), 0x0a (ASCII newline) and 0x0d (ASCII carriage return). The 443 sequence CRLF (0x0d0a) is used to end a record, although parsers 444 SHOULD be tolerant and also accept records terminated with a single 445 newline character. If the "a=charset" attribute is not present, 446 these octet strings MUST be interpreted as containing ISO-10646 447 characters in UTF-8 encoding (the presence of the "a=charset" 448 attribute MAY force some fields to be interpreted differently). 450 A session description can contain domain names in the "o=", "u=", 451 "e=", "c=" and "a=" lines. Any domain name used in SDP MUST comply 452 with [1], [2]. Internationalised domain names (IDNs) MUST be 453 represented using the ASCII Compatible Encoding (ACE) form defined in 454 [11] and MUST NOT be directly represented in UTF-8 or any other 455 encoding (this requirement is for compatibility with RFC 2327 and 456 other SDP-related standards, which predate the development of 457 internationalized domain names). 459 5.1 Protocol Version ("v=") 461 v=0 463 The "v=" field gives the version of the Session Description Protocol. 464 This memo defines version 0. There is no minor version number. 466 5.2 Origin ("o=") 468 o= 469 471 The "o=" field gives the originator of the session (her username and 472 the address of the user's host) plus a session identifier and version 473 number: 475 is the user's login on the originating host, or it is "-" 476 if the originating host does not support the concept of user ids. 477 The MUST NOT contain spaces. 479 is a numeric string such that the tuple of , 480 , , and form a 481 globally unique identifier for the session. The method of 482 allocation is up to the creating tool, but it has been 483 suggested that a Network Time Protocol (NTP) format timestamp be 484 used to ensure uniqueness [13]. 486 is a version number for this session description. Its 487 usage is up to the creating tool, so long as is 488 increased when a modification is made to the session data. Again, 489 it is RECOMMENDED that an NTP format timestamp is used. 491 is a text string giving the type of network. Initially 492 "IN" is defined to have the meaning "Internet", but other values 493 MAY be registered in future (see Section 8). 495 is a text string giving the type of the address that 496 follows. Initially "IP4" and "IP6" are defined, but other values 497 MAY be registered in future (see Section 8). 499 is the address of the machine from which the 500 session was created. For an address type of IP4, this is either 501 the fully-qualified domain name of the machine, or the dotted- 502 decimal representation of the IP version 4 address of the machine. 503 For an address type of IP6, this is either the fully-qualified 504 domain name of the machine, or the compressed textual 505 representation of the IP version 6 address of the machine. For 506 both IP4 and IP6, the fully-qualified domain name is the form that 507 SHOULD be given unless this is unavailable, in which case the 508 globally unique address MAY be substituted. A local IP address 509 MUST NOT be used in any context where the SDP description might 510 leave the scope in which the address is meaningful. 512 In general, the "o=" field serves as a globally unique identifier for 513 this version of this session description, and the subfields excepting 514 the version taken together identify the session irrespective of any 515 modifications. 517 For privacy reasons, it is sometimes desirable to obfuscate the 518 username and IP address of the session originator. If this is a 519 concern, an arbitrary and private MAY be 520 chosen to populate the "o=" field, provided these are selected in a 521 manner that does not affect the global uniqueness of the field. 523 5.3 Session Name ("s=") 525 s= 527 The "s=" field is the textual session name. There MUST be one and 528 only one "s=" field per session description. The "s=" field MUST NOT 529 be empty and SHOULD contain ISO 10646 characters (but see also the 530 "a=charset" attribute). If a session has no meaningful name, the 531 value "s= " SHOULD be used (i.e. a single space as the session name). 533 5.4 Session Information ("i=") 535 i= 537 The "i=" field provides textual information about the session. There 538 MUST be at most one session-level "i=" field per session description, 539 and at most one "i=" field per media. If the "a=charset" attribute 540 is present, it specifies the character set used in the "i=" field. 541 If the "a=charset" attribute is not present, the "i=" field MUST 542 contain ISO 10646 characters in UTF-8 encoding. 544 A single "i=" field MAY also be used for each media definition. In 545 media definitions, "i=" fields are primarily intended for labelling 546 media streams. As such, they are most likely to be useful when a 547 single session has more than one distinct media stream of the same 548 media type. An example would be two different whiteboards, one for 549 slides and one for feedback and questions. 551 The "i=" field is intended to provide a free-form human readable 552 description of the session or the purpose of a media stream. It is 553 not suitable for parsing by automata. 555 5.5 URI ("u=") 557 u= 559 A URI is a Universal Resource Identifier as used by WWW clients [7], 560 [9]. The URI should be a pointer to additional information about the 561 session. This field is OPTIONAL, but if it is present it MUST be 562 specified before the first media field. No more than one URI field 563 is allowed per session description. 565 5.6 Email Address and Phone Number ("e=" and "p=") 567 e= 568 p= 570 The "e=" and "p=" lines specify contact information for the person 571 responsible for the conference. This is not necessarily the same 572 person that created the conference announcement. 574 Inclusion of an email address or phone number is OPTIONAL. Note that 575 the previous version of SDP specified that either an email field or a 576 phone field MUST be specified, but this was widely ignored. The 577 change brings the specification into line with common usage. 579 If the email address or phone number are present, they MUST be 580 specified before the first media field. More than one email or phone 581 field can be given for a session description. 583 Phone numbers SHOULD be given in the form of an international public 584 telecommunication number (see ITU-T Recommendation E.164) preceded by 585 a "+". Spaces and hyphens may be used to split up a phone field to 586 aid readability if desired. For example: 588 p=+1 617 555-6011 590 Both email addresses and phone numbers can have an OPTIONAL free text 591 string associated with them, normally giving the name of the person 592 who may be contacted. This MUST be enclosed in parenthesis if it is 593 present. For example: 595 e=j.doe@example.com (Jane Doe) 597 The alternative RFC 2822 name quoting convention is also allowed for 598 both email addresses and phone numbers. For example: 600 e=Jane Doe 602 The free text string SHOULD be in the ISO-10646 character set with 603 UTF-8 encoding, or alternatively in ISO-8859-1 or other encodings if 604 the appropriate session-level "a=charset" attribute is set. 606 5.7 Connection Data ("c=") 608 c= 610 The "c=" field contains connection data. 612 A session description MUST contain either at least one "c=" field in 613 each media description or a single "c=" field at the session level. 614 It MAY contain a single session-level "c=" field and additional "c=" 615 field(s) per media description, in which case the per-media values 616 override the session-level settings for the respective media. 618 The first sub-field ("") is the network type, which is a 619 text string giving the type of network. Initially "IN" is defined to 620 have the meaning "Internet", but other values MAY be registered in 621 the future (see Section 8). 623 The second sub-field ("") is the address type. This allows 624 SDP to be used for sessions that are not IP based. This memo only 625 defines IP4 and IP6, but other values MAY be registered in the future 626 (see Section 8). 628 The third sub-field ("") is the connection 629 address. OPTIONAL sub-fields MAY be added after the connection 630 address depending on the value of the field. 632 When the is IP4 and IP6, the connection address is defined 633 as follows: 635 o If the session is multicast, the connection address will be an IP 636 multicast group address. If the session is not multicast, then 637 the connection address contains the unicast IP address of the 638 expected data source or data relay or data sink as determined by 639 additional attribute fields. It is not expected that unicast 640 addresses will be given in a session description that is 641 communicated by a multicast announcement, though this is not 642 prohibited. 644 o Sessions using an IPv4 multicast connection address MUST also have 645 a time to live (TTL) value present in addition to the multicast 646 address. The TTL and the address together define the scope with 647 which multicast packets sent in this conference will be sent. TTL 648 values MUST be in the range 0-255. While the TTL MUST be 649 specified, its use to scope multicast traffic is deprecated; 650 applications SHOULD use an administratively scoped address 651 instead. 653 The TTL for the session is appended to the address using a slash as a 654 separator. An example is: 656 c=IN IP4 224.2.36.42/127 658 IPv6 multicast does not use TTL scoping, and hence the TTL value MUST 659 NOT be present for IPv6 multicast. It is expected that IPv6 scoped 660 addresses will be used to limit the scope of conferences. 662 Hierarchical or layered encoding schemes are data streams where the 663 encoding from a single media source is split into a number of layers. 664 The receiver can choose the desired quality (and hence bandwidth) by 665 only subscribing to a subset of these layers. Such layered encodings 666 are normally transmitted in multiple multicast groups to allow 667 multicast pruning. This technique keeps unwanted traffic from sites 668 only requiring certain levels of the hierarchy. For applications 669 requiring multiple multicast groups, we allow the following notation 670 to be used for the connection address: 672 [/]/ 674 If the number of addresses is not given it is assumed to be one. 675 Multicast addresses so assigned are contiguously allocated above the 676 base address, so that, for example: 678 c=IN IP4 224.2.1.1/127/3 680 would state that addresses 224.2.1.1, 224.2.1.2 and 224.2.1.3 are to 681 be used at a TTL of 127. This is semantically identical to including 682 multiple "c=" lines in a media description: 684 c=IN IP4 224.2.1.1/127 685 c=IN IP4 224.2.1.2/127 686 c=IN IP4 224.2.1.3/127 688 Similarly, an IPv6 example would be: 690 c=IN IP6 FF15::101/3 692 which is semantically equivalent to: 694 c=IN IP6 FF15::101 695 c=IN IP6 FF15::102 696 c=IN IP6 FF15::103 698 (remembering that the TTL field is not present in IPv6 multicast). 700 Multiple addresses or "c=" lines MAY be specified on a per-media 701 basis only if they provide multicast addresses for different layers 702 in a hierarchical or layered encoding scheme. They MUST NOT be 703 specified for a session-level "c=" field. 705 The slash notation for multiple addresses described above MUST NOT be 706 used for IP unicast addresses. 708 5.8 Bandwidth ("b=") 709 b=: 711 This OPTIONAL field denotes the proposed bandwidth to be used by the 712 session or media. The is an alphanumeric modifier giving 713 the meaning of the figure. Two values are defined in 714 this specification, but other values MAY be registered in future (see 715 Section 8 and [20], [24]): 717 CT If the bandwidth of a session or media in a session is different 718 from the bandwidth implicit from the scope, a "b=CT:..." line 719 SHOULD be supplied for the session giving the proposed upper limit 720 to the bandwidth used (the "conference total" bandwidth). The 721 primary purpose of this is to give an approximate idea as to 722 whether two or more sessions can co-exist simultaneously. When 723 using the CT modifier with RTP, if several RTP sessions are part 724 of the conference, the conference total refers to total bandwidth 725 of all RTP sessions. 727 AS The bandwidth is interpreted to be application-specific (it will 728 be the application's concept of maximum bandwidth). Normally this 729 will coincide with what is set on the application's "maximum 730 bandwidth" control if applicable. For RTP based applications, AS 731 gives the RTP "session bandwidth" as defined in Section 6.2 of 732 [18]. 734 Note that CT gives a total bandwidth figure for all the media at all 735 sites. AS gives a bandwidth figure for a single media at a single 736 site, although there may be many sites sending simultaneously. 738 A prefix "X-" is defined for names. This is intended for 739 experimental purposes only. For example: 741 b=X-YZ:128 743 Use of the "X-" prefix is NOT RECOMMENDED: instead new modifiers 744 SHOULD be registered with IANA in the standard namespace. SDP 745 parsers MUST ignore bandwidth fields with unknown modifiers. 746 Modifiers MUST be alpha-numeric and, although no length limit is 747 given, they are recommended to be short. 749 The is interpreted as kilobits per second by default. 750 The definition of a new modifier MAY specify that the 751 bandwidth is to be interpreted in some alternative unit (the "CT" and 752 "AS" modifiers defined in this memo use the default units). 754 5.9 Timing ("t=") 756 t= 758 The "t=" lines specify the start and stop times for a session. 759 Multiple "t=" lines MAY be used if a session is active at multiple 760 irregularly spaced times; each additional "t=" lines specifies an 761 additional period of time for which the session will be active. If 762 the session is active at regular times, an "r=" line (see below) 763 should be used in addition to, and following, a "t=" line - in which 764 case the "t=" line specifies the start and stop times of the repeat 765 sequence. 767 The first and second sub-fields give the start and stop times for the 768 session respectively. These values are the decimal representation of 769 Network Time Protocol (NTP) time values in seconds since 1900 [13]. 770 To convert these values to UNIX time, subtract decimal 2208988800. 772 NTP timestamps are elsewhere represented by 64 bit values which wrap 773 sometime in the year 2036. Since SDP uses an arbitrary length 774 decimal representation, this should not cause an issue (SDP 775 timestamps MUST continue counting seconds since 1900, NTP will use 776 the value modulo the 64 bit limit). 778 If the is set to zero, then the session is not bounded, 779 though it will not become active until after the . If 780 the is also zero, the session is regarded as permanent. 782 User interfaces SHOULD strongly discourage the creation of unbounded 783 and permanent sessions as they give no information about when the 784 session is actually going to terminate, and so make scheduling 785 difficult. 787 The general assumption may be made, when displaying unbounded 788 sessions that have not timed out to the user, that an unbounded 789 session will only be active until half an hour from the current time 790 or the session start time, whichever is the later. If behaviour 791 other than this is required, an end-time SHOULD be given and modified 792 as appropriate when new information becomes available about when the 793 session should really end. 795 Permanent sessions may be shown to the user as never being active 796 unless there are associated repeat times which state precisely when 797 the session will be active. In general, permanent sessions SHOULD 798 NOT be created for any session expected to have a duration of less 799 than 2 months, and should be discouraged for sessions expected to 800 have a duration of less than 6 months. 802 5.10 Repeat Times ("r=") 804 r= 806 "r=" fields specify repeat times for a session. For example, if a 807 session is active at 10am on Monday and 11am on Tuesday for one hour 808 each week for three months, then the in the 809 corresponding "t=" field would be the NTP representation of 10am on 810 the first Monday, the would be 1 week, the would be 1 hour, and the offsets would be zero and 25 812 hours. The corresponding "t=" field stop time would be the NTP 813 representation of the end of the last session three months later. By 814 default all fields are in seconds, so the "r=" and "t=" fields might 815 be: 817 t=3034423619 3042462419 818 r=604800 3600 0 90000 820 To make description more compact, times may also be given in units of 821 days, hours or minutes. The syntax for these is a number immediately 822 followed by a single case-sensitive character. Fractional units are 823 not allowed - a smaller unit should be used instead. The following 824 unit specification characters are allowed: 826 d - days (86400 seconds) 827 h - hours (3600 seconds) 828 m - minutes (60 seconds) 829 s - seconds (allowed for completeness but NOT RECOMMENDED) 831 Thus, the above session announcement could also have been written: 833 r=7d 1h 0 25h 835 Monthly and yearly repeats cannot be directly specified with a single 836 SDP repeat time - instead separate "t=" fields should be used to 837 explicitly list the session times. 839 5.11 Time Zones ("z=") 841 z= .... 843 To schedule a repeated session which spans a change from daylight 844 saving time to standard time or vice-versa, it is necessary to 845 specify offsets from the base time. This is required because 846 different time zones change time at different times of day, different 847 countries change to or from daylight time on different dates, and 848 some countries do not have daylight saving time at all. 850 Thus in order to schedule a session that is at the same time winter 851 and summer, it must be possible to specify unambiguously by whose 852 time zone a session is scheduled. To simplify this task for 853 receivers, we allow the sender to specify the NTP time that a time 854 zone adjustment happens and the offset from the time when the session 855 was first scheduled. The "z=" field allows the sender to specify a 856 list of these adjustment times and offsets from the base time. 858 An example might be: 860 z=2882844526 -1h 2898848070 0 862 This specifies that at time 2882844526 the time base by which the 863 session's repeat times are calculated is shifted back by 1 hour, and 864 that at time 2898848070 the session's original time base is restored. 865 Adjustments are always relative to the specified start time - they 866 are not cumulative. Adjustments apply to all "t=" and "r=" lines in 867 a session description. 869 If a session is likely to last several years, it is expected that the 870 session announcement will be modified periodically rather than 871 transmit several years worth of adjustments in one session 872 announcement. 874 5.12 Encryption Keys ("k=") 876 k= 877 k=: 879 If transported over a secure and trusted channel, the session 880 description protocol MAY be used to convey encryption keys. A simple 881 mechanism for key exchange is provided by the key field ("k=") 882 although this is primarily supported for compatibility with older 883 implementations and its use is NOT RECOMMENDED. Work is in progress 884 to define new key exchange mechanisms for use with SDP [26] [27] and 885 it is expected that new applications will use those mechanisms. 887 A key field is permitted before the first media entry (in which case 888 it applies to all media in the session), or for each media entry as 889 required. The format of keys and their usage is outside the scope of 890 this document, and the key field provides no way to indicate the 891 encryption algorithm to be used, key type, or other information about 892 the key: this is assumed to be provided by the higher-level protocol 893 using SDP. If there is a need to convey this information within SDP, 894 the extensions mentioned previously SHOULD be used. Many security 895 protocols require two keys: one for confidentiality, another for 896 integrity. This specification does not support transfer of two keys. 898 The method indicates the mechanism to be used to obtain a usable key 899 by external means, or from the encoded encryption key given. The 900 following methods are defined: 902 k=clear: 904 The encryption key is included untransformed in this key field. 905 This method MUST NOT be used unless it can be guaranteed that 906 the SDP is conveyed over a secure channel. The encryption key 907 is interpreted as text according to the charset attribute, use 908 the "k=base64:" method to convey characters that are otherwise 909 prohibited in SDP. 911 k=base64: 913 The encryption key is included in this key field but has been 914 base64 encoded [12] because it includes characters that are 915 prohibited in SDP. This method MUST NOT be used unless it can 916 be guaranteed that the SDP is conveyed over a secure channel. 918 k=uri: 920 A Universal Resource Identifier is included in the key field. 921 The URI refers to the data containing the key, and may require 922 additional authentication before the key can be returned. When 923 a request is made to the given URI, the reply should specify 924 the encoding for the key. The URI is often a secure HTTP URI, 925 although this is not required. 927 k=prompt 929 No key is included in this SDP description, but the session or 930 media stream referred to by this key field is encrypted. The 931 user should be prompted for the key when attempting to join the 932 session, and this user-supplied key should then be used to 933 decrypt the media streams. The use of user-specified keys is 934 NOT RECOMMENDED, since such keys tend to have weak security 935 properties. 937 The key field MUST NOT be used unless it can be guaranteed that the 938 SDP is conveyed over a secure and trusted channel. An example of 939 such a channel might be SDP embedded inside an S/MIME message or a 940 TLS-protected HTTP session. It is important to ensure that the 941 secure channel is with the party that is authorised to join the 942 session, not an intermediary: if a caching proxy server is used, it 943 is important to ensure that the proxy is either trusted or unable to 944 access the SDP. Definition of appropriate security measures is 945 beyond the scope of this specification, and should be defined by the 946 users of SDP. 948 5.13 Attributes ("a=") 950 a= 951 a=: 953 Attributes are the primary means for extending SDP. Attributes may 954 be defined to be used as "session-level" attributes, "media-level" 955 attributes, or both. 957 A media description may have any number of attributes ("a=" fields) 958 which are media specific. These are referred to as "media-level" 959 attributes and add information about the media stream. Attribute 960 fields can also be added before the first media field; these 961 "session-level" attributes convey additional information that applies 962 to the conference as a whole rather than to individual media. 964 Attribute fields may be of two forms: 966 o A property attribute is simply of the form "a=". These are 967 binary attributes, and the presence of the attribute conveys that 968 the attribute is a property of the session. An example might be 969 "a=recvonly". 971 o A value attribute is of the form "a=:". For 972 example, a whiteboard could have the value attribute "a=orient: 973 landscape" 975 Attribute interpretation depends on the media tool being invoked. 976 Thus receivers of session descriptions should be configurable in 977 their interpretation of session descriptions in general and of 978 attributes in particular. 980 Attribute names MUST use the US-ASCII subset of ISO-10646/UTF-8. 982 Attribute values are octet strings, and MAY use any octet value 983 except 0x00 (Nul), 0x0A (LF), and 0x0D (CR). By default, attribute 984 values are to be interpreted as in ISO-10646 character set with UTF-8 985 encoding. Unlike other text fields, attribute values are NOT 986 normally affected by the "charset" attribute as this would make 987 comparisons against known values problematic. However, when an 988 attribute is defined, it can be defined to be charset-dependent, in 989 which case its value should be interpreted in the session charset 990 rather than in ISO-10646. 992 Attributes MUST be registered with IANA (see Section 8). If an 993 attribute is received that is not understood, it MUST be ignored by 994 the receiver. 996 5.14 Media Descriptions ("m=") 998 m= ... 1000 A session description may contain a number of media descriptions. 1001 Each media description starts with an "m=" field, and is terminated 1002 by either the next "m=" field or by the end of the session 1003 description. A media field has several sub-fields: 1005 is the media type. Currently defined media are "audio", 1006 "video", "text", "application" and "message", although this list 1007 may be extended in future (see Section 8). 1009 is the transport port to which the media stream is sent. The 1010 meaning of the transport port depends on the network being used as 1011 specified in the relevant "c=" field, and on the transport 1012 protocol defined in the sub-field of the media field. 1013 Other ports used by the media application (such as the RTCP port 1014 [18]) MAY be derived algorithmically from the base media port or 1015 MAY be specified in a separate attribute (for example "a=rtcp:" as 1016 defined in [21]). 1018 If non-contiguous ports are used or if they don't follow the 1019 parity rule of even RTP ports and odd RTCP ports, the "a=rtcp:" 1020 attribute MUST be used. Applications that are requested to send 1021 media to a that is odd and where the "a=rtcp:" is present 1022 MUST NOT substract 1 to the RTP port: i.e, they MUST send the RTP 1023 to the port indicated in and send the RTCP to the port 1024 indicated in the "a=rtcp" attribute. 1026 For applications where hierarchically encoded streams are being 1027 sent to a unicast address, it may be necessary to specify multiple 1028 transport ports. This is done using a similar notation to that 1029 used for IP multicast addresses in the "c=" field: 1031 m= / ... 1033 In such a case, the ports used depend on the transport protocol. 1034 For RTP, the default is that only the even numbered ports are used 1035 for data with the corresponding one-higher odd ports used for the 1036 RTCP belonging to the RTP session, and the 1037 denoting the number of RTP sessions. For example: 1039 m=video 49170/2 RTP/AVP 31 1041 would specify that ports 49170 and 49171 form one RTP/RTCP pair 1042 and 49172 and 49173 form the second RTP/RTCP pair. RTP/AVP is the 1043 transport protocol and 31 is the format (see below). If non- 1044 contiguous ports are required, they must be signalled using a 1045 separate attribute (for example "a=rtcp:" as defined in [21]). 1047 If multiple addresses are specified in the "c=" field and multiple 1048 ports are specified in the "m=" field, a one-to-one mapping from 1049 port to the corresponding address is implied. For example: 1051 c=IN IP4 224.2.1.1/127/2 1052 m=video 49170/2 RTP/AVP 31 1054 would imply that address 224.2.1.1 is used with ports 49170 and 1055 49171, and address 224.2.1.2 is used with ports 49172 and 49173. 1057 The combination of ports specified in "m=" lines and IP addresses 1058 specified in "c=" lines MUST comply with the following rules for 1059 RTP-based media streams (other protocols SHOULD define similar 1060 rules): 1062 1. If two media sessions have the same transport address (i.e. 1063 identical IP address and port numbers), the associated payload 1064 types (e.g. given in the "a=rtpmap:" attribute) MUST NOT be in 1065 conflict, i.e. the same payload type MUST NOT be mapped to 1066 different media types. 1068 2. If two media sessions have the same transport address, they 1069 MUST use compatible media (e.g. both audio or both video). 1071 3. If two media sessions have the same transport address, they 1072 SHOULD operate under the same RTP profile. The sessions MAY 1073 use two different RTP profiles only if those profiles are 1074 specifically designed to be compatible. 1076 4. If two media sessions have the same RTP transport address, 1077 they MUST also use the same RTCP address and vice versa. 1079 Two media sessions with the same transport address indicate 1080 alternatives for the same media stream, i.e. all profiles, media 1081 types, and payload types provided in any of the "m=" lines are 1082 valid. 1084 is the transport protocol. The meaning of the transport 1085 protocol is dependent on the address type field in the relevant 1086 "c=" field. Thus a "c=" field of IP4 indicates that the transport 1087 protocol runs over IP4. The following transport protocols are 1088 defined, but may be extended through registration of new protocols 1089 with IANA (see Section 8): 1091 * udp: denotes an unspecified protocol running over UDP. 1093 * RTP/AVP: denotes RTP [18] used under the RTP Profile for Audio 1094 and Video Conferences with Minimal Control [19] running over 1095 UDP. 1097 * RTP/SAVP: denotes the Secure Real-time Transport Protocol [22] 1098 running over UDP. 1100 The main reason to specify the transport-protocol in addition to 1101 the media format is that the same standard media formats may be 1102 carried over different transport protocols even when the network 1103 protocol is the same - a historical example is vat PCM audio and 1104 RTP PCM audio, another might be TCP/RTP PCM audio. In addition, 1105 relays and monitoring tools that are transport-protocol-specific 1106 but format-independent are possible. 1108 is a media format description. The fourth and any subsequent 1109 sub-fields describe the format of the media. The interpretation 1110 of the media format depends on the value of the sub-field. 1112 If the sub-field is "RTP/AVP" or "RTP/SAVP" the sub- 1113 fields contain RTP payload type numbers. When a list of payload 1114 type numbers is given, this implies that all of these payload 1115 formats MAY be used in the session, but the first of these formats 1116 SHOULD be used as the default format for the session. For dynamic 1117 payload type assignments the "a=rtpmap:" attribute (see Section 6) 1118 SHOULD be used to map from an RTP payload type number to a media 1119 encoding name that identifies the payload format. The "a=fmtp:" 1120 attribute MAY be used to specify format parameters (see 1121 Section 6). 1123 If the sub-field is "udp" the sub-fields MUST 1124 reference a media type describing the format under the "audio", 1125 "video", "text", "application" or "message" top-level MIME types. 1126 The media type registration SHOULD define the packet format for 1127 use with UDP transport. 1129 For media using other transport protocols, the field is 1130 protocol specific. Rules for interpretation of the sub- 1131 field MUST be defined when registering new protocols (see section 1132 8.2.2). 1134 6. SDP Attributes 1136 The following attributes are defined. Since application writers may 1137 add new attributes as they are required, this list is not exhaustive. 1138 Registration procedures for new attributes are defined in Section 1139 8.2.4. 1141 a=cat: 1143 This attribute gives the dot-separated hierarchical category 1144 of the session. This is to enable a receiver to filter 1145 unwanted sessions by category. It is a session-level 1146 attribute, and is not dependent on charset. 1148 a=keywds: 1150 Like the cat attribute, this is to assist identifying wanted 1151 sessions at the receiver. This allows a receiver to select 1152 interesting session based on keywords describing the purpose 1153 of the session. It is a session-level attribute. It is a 1154 charset dependent attribute, meaning that its value should be 1155 interpreted in the charset specified for the session 1156 description if one is specified, or by default in ISO 1157 10646/UTF-8. 1159 a=tool: 1161 This gives the name and version number of the tool used to 1162 create the session description. It is a session-level 1163 attribute, and is not dependent on charset. 1165 a=ptime: 1167 This gives the length of time in milliseconds represented by 1168 the media in a packet. This is probably only meaningful for 1169 audio data, but may be used with other media types if it makes 1170 sense. It should not be necessary to know ptime to decode RTP 1171 or vat audio, and it is intended as a recommendation for the 1172 encoding/packetisation of audio. It is a media attribute, and 1173 is not dependent on charset. 1175 a=maxptime: 1176 The maximum amount of media which can be encapsulated in each 1177 packet, expressed as time in milliseconds. The time SHALL be 1178 calculated as the sum of the time the media present in the 1179 packet represents. For frame based codecs, the time SHOULD 1180 be an integer multiple of the frame size. This attribute is 1181 probably only meaningful for audio data, but may be used with 1182 other media types if it makes sense. It is a media attribute, 1183 and is not dependent on charset. Note that this attribute was 1184 introduced after RFC 2327, and non updated implementations will 1185 ignore this attribute. 1187 a=rtpmap: / 1188 [/] 1190 This attribute maps from an RTP payload type number (as used in 1191 an "m=" line) to an encoding name denoting the payload format 1192 to be used. It also provides information on the clock rate and 1193 encoding parameters. It is a media level attribute that is not 1194 dependent on charset. 1196 While an RTP profile may make static assignments of payload 1197 type numbers to payload formats, it is more common for that 1198 assignment to be done dynamically using "a=rtpmap:" attributes. 1199 As an example of a static payload type, consider u-law PCM 1200 coded single channel audio sampled at 8kHz. This is completely 1201 defined in the RTP Audio/Video profile as payload type 0, so 1202 there is no need for an "a=rtpmap: attribute, and the media for 1203 such a stream sent to UDP port 49232 can be specified as: 1205 m=audio 49232 RTP/AVP 0 1207 An example of a dynamic payload type is 16 bit linear encoded 1208 stereo audio sampled at 16 kHz. If we wish to use the dynamic 1209 RTP/AVP payload type 98 for this stream, additional information 1210 is required to decode it: 1212 m=audio 49232 RTP/AVP 98 1213 a=rtpmap:98 L16/16000/2 1215 Up to one rtpmap attribute can be defined for each media format 1216 specified. Thus we might have: 1218 m=audio 49230 RTP/AVP 96 97 98 1219 a=rtpmap:96 L8/8000 1220 a=rtpmap:97 L16/8000 1221 a=rtpmap:98 L16/11025/2 1223 RTP profiles that specify the use of dynamic payload types MUST 1224 define the set of valid encoding names and/or a means to 1225 register encoding names if that profile is to be used with SDP. 1226 The "RTP/AVP" and "RTP/SAVP" profiles use MIME sub-types for 1227 encoding names, under the top-level media type denoted in the 1228 "m=" line. In the example above, the media types are "audio/l8" 1229 and "audio/l16". 1231 For audio streams, indicates the 1232 number of audio channels. This parameter is OPTIONAL and 1233 may be omitted if the number of channels is one, provided 1234 no additional parameters are needed. 1236 For video streams, no encoding parameters are currently 1237 specified. 1239 Additional encoding parameters MAY be defined in the future, 1240 but codec specific parameters SHOULD NOT be added. Parameters 1241 added to an "a=rtpmap:" attribute SHOULD only be those required 1242 for a session directory to make the choice of appropriate media 1243 to participate in a session. Codec-specific parameters should 1244 be added in other attributes (for example, "a=fmtp:"). 1246 Note: RTP audio formats typically do not include information 1247 about the number of samples per packet. If a non-default (as 1248 defined in the RTP Audio/Video Profile) packetisation is 1249 required, the "ptime" attribute is used as given below. 1251 a=recvonly 1253 This specifies that the tools should be started in receive 1254 only mode where applicable. It can be either a session or 1255 media attribute, and is not dependent on charset. Note that 1256 recvonly applies to the media only, not to any associated 1257 control protocol (e.g. an RTP based system in recvonly mode 1258 SHOULD still send RTCP packets). 1260 a=sendrecv 1262 This specifies that the tools should be started in send and 1263 receive mode. This is necessary for interactive conferences 1264 with tools that default to receive only mode. It can be either 1265 a session or media attribute, and is not dependent on charset. 1267 If none of the attributes "sendonly", "recvonly", "inactive", 1268 and "sendrecv" is present, "sendrecv" SHOULD be assumed as the 1269 default for sessions which are not of the conference type 1270 "broadcast" or "H332" (see below). 1272 a=sendonly 1274 This specifies that the tools should be started in send-only 1275 mode. An example may be where a different unicast address is 1276 to be used for a traffic destination than for a traffic 1277 source. In such a case, two media descriptions may be used, 1278 one sendonly and one recvonly. It can be either a session or 1279 media attribute, but would normally only be used as a media 1280 attribute. It is not dependent on charset. Note that sendonly 1281 applies only to the media, and any associated control protocol 1282 (e.g. RTCP) SHOULD still be received and processed as normal. 1284 a=inactive 1286 This specifies that the tools should be started in inactive 1287 mode. This is necessary for interactive conferences where 1288 users can put other users on hold. No media is sent over an 1289 inactive media stream. Note that an RTP based system SHOULD 1290 still send RTCP, even if started inactive. It can be either a 1291 session or media attribute, and is not dependent on charset. 1293 a=orient: 1295 Normally this is only used for a whiteboard or presentation 1296 tool. It specifies the orientation of a the workspace on 1297 the screen. It is a media attribute. Permitted values are 1298 "portrait", "landscape" and "seascape" (upside down landscape). 1299 It is not dependent on charset. 1301 a=type: 1303 This specifies the type of the conference. Suggested values 1304 are "broadcast", "meeting", "moderated", "test" and "H332". 1305 "recvonly" should be the default for "type:broadcast" 1306 sessions, "type:meeting" should imply "sendrecv" and 1307 "type:moderated" should indicate the use of a floor control 1308 tool and that the media tools are started so as to mute new 1309 sites joining the conference. 1311 Specifying the attribute "type:H332" indicates that this 1312 loosely coupled session is part of a H.332 session as defined 1313 in the ITU H.332 specification [15]. Media tools should be 1314 started "recvonly". 1316 Specifying the attribute "type:test" is suggested as a hint 1317 that, unless explicitly requested otherwise, receivers can 1318 safely avoid displaying this session description to users. 1320 The type attribute is a session-level attribute, and is not 1321 dependent on charset. 1323 a=charset: 1325 This specifies the character set to be used to display the 1326 session name and information data. By default, the ISO-10646 1327 character set in UTF-8 encoding is used. If a more compact 1328 representation is required, other character sets may be used. 1329 For example, the ISO 8859-1 is specified with the following 1330 SDP attribute: 1332 a=charset:ISO-8859-1 1334 This is a session-level attribute and is not dependent on 1335 charset. The charset specified MUST be one of those registered 1336 with IANA, such as ISO-8859-1. The character set identifier is 1337 a US-ASCII string and MUST be compared against the IANA 1338 identifiers using a case insensitive comparison. If the 1339 identifier is not recognised or not supported, all strings that 1340 are affected by it SHOULD be regarded as octet strings. 1342 Note that a character set specified MUST still prohibit the 1343 use of bytes 0x00 (Nul), 0x0A (LF) and 0x0d (CR). Character 1344 sets requiring the use of these characters MUST define a 1345 quoting mechanism that prevents these bytes appearing within 1346 text fields. 1348 a=sdplang: 1350 This can be a session level attribute or a media level 1351 attribute. As a session level attribute, it specifies the 1352 language for the session description. As a media level 1353 attribute, it specifies the language for any media-level SDP 1354 information field associated with that media. Multiple 1355 sdplang attributes can be provided either at session or media 1356 level if multiple languages in the session description or 1357 media use multiple languages, in which case the order of the 1358 attributes indicates the order of importance of the various 1359 languages in the session or media from most important to least 1360 important. 1362 In general, sending session descriptions consisting of 1363 multiple languages is discouraged. Instead, multiple 1364 descriptions SHOULD be sent describing the session, one in 1365 each language. However this is not possible with all 1366 transport mechanisms, and so multiple sdplang attributes are 1367 allowed although NOT RECOMMENDED. 1369 The "sdplang" attribute value must be a single RFC 3066 1370 language tag in US-ASCII [6]. It is not dependent on 1371 the charset attribute. An "sdplang" attribute SHOULD be 1372 specified when a session is of sufficient scope to cross 1373 geographic boundaries where the language of recipients cannot 1374 be assumed, or where the session is in a different language 1375 from the locally assumed norm. 1377 a=lang: 1379 This can be a session level attribute or a media level 1380 attribute. As a session level attribute, it specifies the 1381 default language for the session being described. As a media 1382 level attribute, it specifies the language for that media, 1383 overriding any session-level language specified. Multiple 1384 lang attributes can be provided either at session or media 1385 level if the session description or media use multiple 1386 languages, in which case the order of the attributes indicates 1387 the order of importance of the various languages in the 1388 session or media from most important to least important. 1390 The "lang" attribute value must be a single RFC 3066 language 1391 tag in US-ASCII [6]. It is not dependent on the charset 1392 attribute. A "lang" attribute SHOULD be specified when a 1393 session is of sufficient scope to cross geographic boundaries 1394 where the language of recipients cannot be assumed, or where 1395 the session is in a different language from the locally 1396 assumed norm. 1398 a=framerate: 1400 This gives the maximum video frame rate in frames/sec. It is 1401 intended as a recommendation for the encoding of video data. 1402 Decimal representations of fractional values using the 1403 notation "." are allowed. It is a 1404 media attribute, defined only for video media, and is not 1405 dependent on charset. 1407 a=quality: 1409 This gives a suggestion for the quality of the encoding as an 1410 integer value. The intention of the quality attribute for 1411 video is to specify a non-default trade-off between frame-rate 1412 and still-image quality. For video, the value in the range 0 1413 to 10, with the following suggested meaning: 1415 10 - the best still-image quality the compression scheme 1416 can give. 1418 5 - the default behaviour given no quality suggestion. 1419 0 - the worst still-image quality the codec designer 1420 thinks is still usable. 1422 It is a media attribute, and is not dependent on charset. 1424 a=fmtp: 1426 This attribute allows parameters that are specific to a 1427 particular format to be conveyed in a way that SDP doesn't 1428 have to understand them. The format must be one of the 1429 formats specified for the media. Format-specific parameters 1430 may be any set of parameters required to be conveyed by SDP 1431 and given unchanged to the media tool that will use this 1432 format. At most one instance of this attribute is allowed 1433 for each format. 1435 It is a media attribute, and is not dependent on charset. 1437 7. Security Considerations 1439 SDP is frequently used with the Session Initiation Protocol [15] 1440 using the offer/answer model [17] to agree parameters for unicast 1441 sessions. When used in this manner, the security considerations of 1442 those protocols apply. 1444 SDP is a session description format that describes multimedia 1445 sessions. A session description SHOULD NOT be trusted unless it has 1446 been obtained by an authenticated transport protocol from a trusted 1447 source. Many different transport protocols may be used to distribute 1448 session description, and the nature of the authentication will differ 1449 from transport to transport. 1451 One transport that will frequently be used to distribute session 1452 descriptions is the Session Announcement Protocol (SAP). SAP 1453 provides both encryption and authentication mechanisms but due to the 1454 nature of session announcements it is likely that there are many 1455 occasions where the originator of a session announcement cannot be 1456 authenticated because they are previously unknown to the receiver of 1457 the announcement and because no common public key infrastructure is 1458 available. 1460 On receiving a session description over an unauthenticated transport 1461 mechanism or from an untrusted party, software parsing the session 1462 should take a few precautions. Session descriptions contain 1463 information required to start software on the receivers system. 1464 Software that parses a session description MUST NOT be able to start 1465 other software except that which is specifically configured as 1466 appropriate software to participate in multimedia sessions. It is 1467 normally considered inappropriate for software parsing a session 1468 description to start, on a user's system, software that is 1469 appropriate to participate in multimedia sessions, without the user 1470 first being informed that such software will be started and giving 1471 their consent. Thus a session description arriving by session 1472 announcement, email, session invitation, or WWW page MUST NOT deliver 1473 the user into an interactive multimedia session unless the user has 1474 explicitly pre-authorized such action. As it is not always simple to 1475 tell whether a session is interactive or not, applications that are 1476 unsure should assume sessions are interactive. 1478 In this specification, there are no attributes which would allow the 1479 recipient of a session description to be informed to start multimedia 1480 tools in a mode where they default to transmitting. Under some 1481 circumstances it might be appropriate to define such attributes. If 1482 this is done an application parsing a session description containing 1483 such attributes SHOULD either ignore them, or inform the user that 1484 joining this session will result in the automatic transmission of 1485 multimedia data. The default behaviour for an unknown attribute is 1486 to ignore it. 1488 Session descriptions may be parsed at intermediate systems such as 1489 firewalls for the purposes of opening a hole in the firewall to allow 1490 participation in multimedia sessions. This SHOULD NOT be done unless 1491 the SDP is conveyed in a manner that allows proper authentication and 1492 authorization checks to ensure that firewall holes are only opened in 1493 accordance with applicable security policy. SDP by itself does not 1494 include sufficient information to enable these checks: they depend on 1495 the encapsulating protocol (e.g. SIP or RTSP). 1497 Use of the "k=" field poses a significant security risk, since it 1498 conveys session encryption keys in the clear. SDP MUST NOT be used 1499 to convey key material, unless it can be guaranteed that the channel 1500 over which the SDP is delivered is both private and authenticated. 1502 8. IANA Considerations 1504 8.1 The "application/sdp" media type 1506 One MIME media type registration from RFC 2327 is to be updated, as 1507 defined below. 1509 To: ietf-types@iana.org 1510 Subject: Registration of media type "application/sdp" 1512 MIME media type name: application 1514 MIME subtype name: sdp 1516 Required parameters: None. 1518 Optional parameters: None. 1520 Encoding considerations: 1521 SDP files are primarily 7-bit ASCII text. The "a=charset:" 1522 attribute may be used to signal the presence of other, 1523 possibly 8-bit, text in certain parts of an SDP file (see 1524 section 6 of RFC XXXX). Arbitrary binary content cannot 1525 be directly represented in SDP. 1527 Security considerations: 1528 See section 7 of RFC XXXX 1530 Interoperability considerations: 1531 See RFC XXXX 1533 Published specification: 1534 See RFC XXXX 1536 Applications which use this media type: 1537 Voice over IP, video teleconferencing, streaming media, instant 1538 messaging, etc. See also section 3 of RFC XXXX. 1540 Additional information: 1542 Magic number(s): None. 1543 File extension(s): The extension ".sdp" is commonly used. 1544 Macintosh File Type Code(s): "sdp " 1546 Person & email address to contact for further information: 1547 Mark Handley 1548 Colin Perkins 1549 IETF MMUSIC working group 1551 Intended usage: COMMON 1553 Author/Change controller: 1554 Authors of RFC XXXX 1555 IETF MMUSIC working group delegated from the IESG 1557 8.2 Registration of Parameters 1559 There are seven field names that may be registered with IANA. Using 1560 the terminology in the SDP specification BNF, they are "media", 1561 "proto", "fmt", "att-field", "bwtype", "nettype" and "addrtype". 1563 8.2.1 Media types ("media") 1565 The set of media types is intended to be small and SHOULD NOT be 1566 extended except under rare circumstances. The same rules should 1567 apply for media names as for top-level MIME content types, and where 1568 possible the same name should be registered for SDP as for MIME. For 1569 media other than existing MIME top-level content types, a standards- 1570 track RFC MUST be produced for a new top-level content type to be 1571 registered, and the registration MUST provide good justification why 1572 no existing media name is appropriate (the "Standards Action" policy 1573 of RFC 2434 [8]. 1575 This memo registers the media types "audio", "video", "text", 1576 "application" and "message". 1578 Note: The media types "control" and "data" were listed as valid in 1579 the previous version of this specification [6], however their 1580 semantics were never fully specified and they are not widely used. 1581 These media types have been removed in this specification, although 1582 they still remain valid media type capabilities for a SIP user agent 1583 as defined in RFC 3840 [23]. If these media types are considered 1584 useful in future, a Standards Track RFC MUST be produced to document 1585 their use. Until that is done, applications SHOULD NOT use these 1586 types and SHOULD NOT declare support for them in SIP capabilities 1587 declarations (even though they exist in the registry created by RFC 1588 3840). 1590 8.2.2 Transport protocols ("proto") 1592 The "proto" field describes the transport protocol used. This SHOULD 1593 reference a standards-track protocol RFC. This memo registers three 1594 values: "RTP/AVP" is a reference to RTP [18] used under the RTP 1595 Profile for Audio and Video Conferences with Minimal Control [19] 1596 running over UDP/IP, "RTP/SAVP" is a reference to the Secure Real- 1597 time Transport Protocol [22], and "udp" indicates an unspecified 1598 protocol over UDP. 1600 If other RTP profiles are defined in the future, their "proto" name 1601 SHOULD be specified in the same manner. For example, an RTP profile 1602 whose short name is "XYZ" would be denoted by a "proto" field of 1603 "RTP/XYZ". 1605 New transport protocols SHOULD be registered with IANA. 1606 Registrations MUST reference an RFC describing the protocol. Such an 1607 RFC MAY be Experimental or Informational, although it is preferable 1608 if it is Standards-Track. Registrations MUST also define the rules 1609 by which their "fmt" namespace is managed (see below). 1611 8.2.3 Media formats ("fmt") 1613 Each transport protocol, defined by the "proto" field, has an 1614 associated "fmt" namespace that describes the media formats which may 1615 conveyed by that protocol. Formats cover all the possible encodings 1616 that might want to be transported in a multimedia session. 1618 RTP payload formats under the "RTP/AVP" and "RTP/SAVP" profiles MUST 1619 use the payload type number as their "fmt" value. If the payload 1620 type number is dynamically assigned by this session description, an 1621 additional "rtpmap" attribute MUST be included to specify the format 1622 name and parameters as defined by the MIME type registration for the 1623 payload format. It is RECOMMENDED that other RTP profiles which are 1624 registered (in combination with RTP) as SDP transport protocols 1625 specify the same rules for the "fmt" namespace. 1627 For the "udp" protocol, new formats SHOULD be registered. Use of an 1628 existing MIME subtype for the format is encouraged. If no MIME 1629 subtype exists, it is RECOMMENDED that a suitable one is registered 1630 through the IETF process (RFC 2048) by production of, or reference 1631 to, a standards-track RFC that defines the transport protocol for the 1632 format. 1634 For other protocols, formats MAY be registered according to the rules 1635 of the associated "proto" specification. 1637 Registrations of new formats MUST specify which transport protocols 1638 they apply to. 1640 8.2.4 Attribute names ("att-field") 1642 Attribute field names ("att-field") MUST be registered with IANA and 1643 documented, because of noticeable issues due to conflicting 1644 attributes under the same name. Unknown attributes in SDP are simply 1645 ignored, but conflicting ones that fragment the protocol are a 1646 serious problem. 1648 New attribute registrations are accepted according to the 1649 "Specification Required" policy of RFC 2434, provided that the 1650 specification includes the following information: 1652 o contact name, email address and telephone number 1654 o attribute-name (as it will appear in SDP) 1656 o long-form attribute name in English 1658 o type of attribute (session level, media level, or both) 1660 o whether the attribute value is subject to the charset attribute. 1662 o a one paragraph explanation of the purpose of the attribute. 1664 o a specification of appropriate attribute values for this 1665 attribute. 1667 The above is the minimum that IANA will accept. Attributes that are 1668 expected to see widespread use and interoperability, SHOULD be 1669 documented with a standards-track RFC that specifies the attribute 1670 more precisely. 1672 Submitters of registrations should ensure that the specification is 1673 in the spirit of SDP attributes, most notably that the attribute is 1674 platform independent in the sense that it makes no implicit 1675 assumptions about operating systems and does not name specific pieces 1676 of software in a manner that might inhibit interoperability. 1678 IANA is requested to register the following initial set of attribute 1679 names ("att-field" values), with definitions as in Section 6 of this 1680 memo (these definitions update those in RFC 2327): 1682 Name | Session or Media level? | Dependent on charset? 1683 ----------+-------------------------+---------------------- 1684 cat | Session | No 1685 keywds | Session | Yes 1686 tool | Session | No 1687 ptime | Media | No 1688 maxptime | Media | No 1689 rtpmap | Media | No 1690 recvonly | Either | No 1691 sendrecv | Either | No 1692 sendonly | Either | No 1693 inactive | Either | No 1694 orient | Media | No 1695 type | Session | No 1696 charset | Session | No 1697 sdplang | Either | No 1698 lang | Either | No 1699 framerate | Media | No 1700 quality | Media | No 1701 fmtp | Media | No 1703 8.2.5 Bandwidth specifiers ("bwtype") 1705 A proliferation of bandwidth specifiers is strongly discouraged. 1707 New bandwidth specifiers ("bwtype" fields) MUST be registered with 1708 IANA. The submission MUST reference a standards-track RFC specifying 1709 the semantics of the bandwidth specifier precisely, and indicating 1710 when it should be used, and why the existing registered bandwidth 1711 specifiers do not suffice. 1713 IANA is requested to register the bandwith specifiers "CT" and "AS" 1714 with definitions as in Section 5.8 of this memo (these definitions 1715 update those in RFC 2327). 1717 8.2.6 Network types ("nettype") 1719 New network types (the "nettype" field) may be registered with IANA 1720 if SDP needs to be used in the context of non-Internet environments. 1721 Whilst these are not normally the preserve of IANA, there may be 1722 circumstances when an Internet application needs to interoperate with 1723 a non- Internet application, such as when gatewaying an Internet 1724 telephony call into the PSTN. The number of network types should be 1725 small and should be rarely extended. A new network type cannot be 1726 registered without registering at least one address type to be used 1727 with that network type. A new network type registration MUST 1728 reference an RFC which gives details of the network type and address 1729 type and specifies how and when they would be used. 1731 IANA is requested to register the network type "IN" to represent the 1732 Internet, with definition as in Sections 5.2 and 5.7 of this memo 1733 (these definitions update those in RFC 2327). 1735 8.2.7 Address types ("addrtype") 1737 New address types ("addrtype") may be registered with IANA. An 1738 address type is only meaningful in the context of a network type, and 1739 any registration of an address type MUST specify a registered network 1740 type, or be submitted along with a network type registration. A new 1741 address type registration MUST reference an RFC giving details of the 1742 syntax of the address type. Address types are not expected to be 1743 registered frequently. 1745 IANA is requested to register the address types "IP4" and "IP6" with 1746 definitions as in Sections 5.2 and 5.7 of this memo (these 1747 definitions update those in RFC 2327). 1749 8.2.8 Registration Procedure 1751 In the RFC documentation that registers SDP "media", "proto", "fmt", 1752 "bwtype", "nettype" and "addrtype" fields, the authors MUST include 1753 the following information for IANA to place in the appropriate 1754 registry: 1756 o contact name, email address and telephone number 1758 o name being registered (as it will appear in SDP) 1760 o long-form name in English 1762 o type of name ("media", "proto", "fmt", "bwtype", "nettype", or 1763 "addrtype") 1765 o a one paragraph explanation of the purpose of the registered name. 1767 o a reference to the specification for the registered name (this 1768 will typically be an RFC number). 1770 IANA may refer any registration to the IESG Transport Area Directors 1771 for review, and may request revisions to be made before a 1772 registration will be made. 1774 8.3 Encryption Key Access Methods 1776 The IANA currently maintains a table of SDP encryption key access 1777 method ("enckey") names. This table is obsolete and SHOULD be 1778 removed, since the "k=" line is not extensible. New registrations 1779 MUST NOT be accepted. 1781 9. SDP Grammar 1783 This section provides an Augmented BNF grammar for SDP. ABNF is 1784 defined in [4]. 1786 ; SDP Syntax 1787 session-description = proto-version 1788 origin-field 1789 session-name-field 1790 information-field 1791 uri-field 1792 email-fields 1793 phone-fields 1794 connection-field 1795 bandwidth-fields 1796 time-fields 1797 key-field 1798 attribute-fields 1799 media-descriptions 1801 proto-version = "v=" 1*DIGIT CRLF 1802 ;this memo describes version 0 1804 origin-field = "o=" username SP sess-id SP sess-version SP 1805 nettype SP addrtype SP unicast-address CRLF 1807 session-name-field = "s=" text CRLF 1809 information-field = ["i=" text CRLF] 1811 uri-field = ["u=" uri CRLF] 1813 email-fields = *("e=" email-address CRLF) 1815 phone-fields = *("p=" phone-number CRLF) 1817 connection-field = ["c=" nettype SP addrtype SP 1818 connection-address CRLF] 1819 ;a connection field must be present 1820 ;in every media description or at the 1821 ;session-level 1823 bandwidth-fields = *("b=" bwtype ":" bandwidth CRLF) 1824 time-fields = 1*( "t=" start-time SP stop-time 1825 *(CRLF repeat-fields) CRLF) 1826 [zone-adjustments CRLF] 1828 repeat-fields = "r=" repeat-interval SP typed-time 1829 1*(SP typed-time) 1831 zone-adjustments = "z=" time SP ["-"] typed-time 1832 *(SP time SP ["-"] typed-time) 1834 key-field = ["k=" key-type CRLF] 1836 attribute-fields = *("a=" attribute CRLF) 1838 media-descriptions = *( media-field 1839 information-field 1840 *connection-field 1841 bandwidth-fields 1842 key-field 1843 attribute-fields ) 1845 media-field = "m=" media SP port ["/" integer] 1846 SP proto 1*(SP fmt) CRLF 1848 ; sub-rules of 'o=' 1849 username = non-ws-string 1850 ;pretty wide definition, but doesn't 1851 ;include space 1853 sess-id = 1*DIGIT 1854 ;should be unique for this username/host 1856 sess-version = 1*DIGIT 1858 nettype = token 1859 ;typically "IN" 1861 addrtype = token 1862 ;typically "IP4" or "IP6" 1864 ; sub-rules of 'u=' 1865 uri = URI-reference 1866 ; see RFC2396 and RFC2732 1868 ; sub-rules of 'e=', see rfc 2822 for definitions 1869 email-address = address-and-comment / dispname-and-address 1870 / addrspec 1871 address-and-comment = addrspec 1*SP "(" 1*email-safe ")" 1872 dispname-and-address = 1*email-safe 1*SP "<" addrspec ">" 1873 addrspec = dot-atom "@" domain 1875 ; sub-rules of 'p=' 1876 phone-number = phone *SP "(" 1*email-safe ")" / 1877 1*email-safe "<" phone ">" / 1878 phone 1880 phone = ["+"] DIGIT 1*(SP / "-" / DIGIT) 1882 ; sub-rules of 'c=' 1883 connection-address = multicast-address / unicast-address 1885 ; sub-rules of 'b=' 1886 bwtype = token 1888 bandwidth = 1*DIGIT 1890 ; sub-rules of 't=' 1891 start-time = time / "0" 1893 stop-time = time / "0" 1895 time = POS-DIGIT 9*DIGIT 1896 ; Decimal representation of NTP time in 1897 ; seconds since 1900. The representation 1898 ; of NTP time is an unbounded length field 1899 ; containing at least 10 digits. Unlike the 1900 ; 64-bit representation used elsewhere, time 1901 ; in SDP does not wrap in the year 2036. 1903 ; sub-rules of 'r=' and 'z=' 1904 repeat-interval = POS-DIGIT *DIGIT [fixed-len-time-unit] 1906 typed-time = 1*DIGIT [fixed-len-time-unit] 1908 fixed-len-time-unit = "d" / "h" / "m" / "s" 1910 ; sub-rules of 'k=' 1911 key-type = "prompt" / 1912 "clear:" text / 1913 "base64:" base64 / 1914 "uri:" uri 1916 base64 = *base64-unit [base64-pad] 1917 base64-unit = 4base64-char 1918 base64-pad = 2base64-char "==" / 3base64-char "=" 1919 base64-char = ALPHA / DIGIT / "+" / "/" 1920 ; sub-rules of 'a=' 1921 attribute = (att-field ":" att-value) / att-field 1923 att-field = token 1925 att-value = byte-string 1927 ; sub-rules of 'm=' 1928 media = token 1929 ;typically "audio", "video", "text" or 1930 ;"application" 1932 fmt = token 1933 ;typically an RTP payload type for audio 1934 ;and video media 1936 proto = token *("/" token) 1937 ;typically "RTP/AVP" or "udp" 1939 port = 1*DIGIT 1941 ; generic sub-rules: addressing 1942 unicast-address = IP4-address / IP6-address / FQDN / extn-addr 1944 multicast-address = IP4-multicast / IP6-multicast / FQDN 1945 / extn-addr 1947 IP4-multicast = m1 3( "." decimal-uchar ) 1948 "/" ttl [ "/" integer ] 1949 ; IPv4 multicast addresses may be in the 1950 ; range 224.0.0.0 to 239.255.255.255 1952 m1 = ("22" ("4"/"5"/"6"/"7"/"8"/"9")) / 1953 ("23" DIGIT ) 1955 IP6-multicast = hexpart [ "/" integer ] 1956 ; IPv6 address starting with FF 1958 ttl = (POS-DIGIT *2DIGIT) / "0" 1960 FQDN = 4*(alpha-numeric / "-" / ".") 1961 ; fully qualified domain name as specified 1962 ; in RFC1035 (and updates) 1964 IP4-address = b1 3("." decimal-uchar) 1966 b1 = decimal-uchar 1967 ; less than "224" 1969 ; The following is from RFC2373 Appendix B. It is a direct copy. 1970 IP6-address = hexpart [ ":" IP4-address ] 1972 hexpart = hexseq / hexseq "::" [ hexseq ] / 1973 "::" [ hexseq ] 1975 hexseq = hex4 *( ":" hex4) 1977 hex4 = 1*4HEXDIG 1979 ; Generic for other address families 1980 extn-addr = non-ws-string 1982 ; generic sub-rules: datatypes 1983 text = byte-string 1984 ;default is to interpret this as UTF8 text. 1985 ;ISO 8859-1 requires "a=charset:ISO-8859-1" 1986 ;session-level attribute to be used 1988 byte-string = 1*(%x01-09/%x0B-0C/%x0E-FF) 1989 ;any byte except NUL, CR or LF 1991 non-ws-string = 1*(VCHAR/%x80-FF) 1992 ;string of visible characters 1994 token-char = %x21 / %x23-27 / %x2A-2B / %x2D-2E / %x30-39 1995 / %x41-5A / %x5E-7E 1997 token = 1*(token-char) 1999 email-safe = %x01-09/%x0B-0C/%x0E-27/%x2A-3B/%x3D/%x3F-FF 2000 ;any byte except NUL, CR, LF, or the quoting 2001 ;characters ()<> 2003 integer = POS-DIGIT *DIGIT 2005 ; generic sub-rules: primitives 2006 alpha-numeric = ALPHA / DIGIT 2008 POS-DIGIT = %x31-39 ; 1 - 9 2010 decimal-uchar = DIGIT 2011 / POS-DIGIT DIGIT 2012 / ("1" 2*(DIGIT)) 2013 / ("2" ("0"/"1"/"2"/"3"/"4") DIGIT) 2014 / ("2" "5" ("0"/"1"/"2"/"3"/"4"/"5")) 2016 ; external references: 2018 ; ALPHA, DIGIT, CRLF, SP, VCHAR: from RFC 2234 2019 ; URI-reference: from RFC2396 and RFC2732 2020 ; addr-spec: from RFC 2822 2022 10. Summary of Changes from RFC 2327 2024 The memo has been significantly restructured, incorporating a large 2025 number of clarifications to the specification in light of use. With 2026 the exception of those items noted below, the changes to the memo are 2027 intended to be backwards compatible clarifications. However, due to 2028 inconsistencies and unclear definitions in RFC 2327 it is likely that 2029 some implementations interpreted that memo in ways that differ from 2030 this version of SDP. 2032 The ABNF grammar in Section 9 has been extensively revised and 2033 updated, correcting a number of mistakes and incorporating the RFC 2034 3266 IPv6 extensions. Known inconsistencies between the grammar and 2035 the specification text have been resolved. 2037 A media type registration for SDP is included. Requirements for the 2038 registration of attributes and other parameters with IANA have been 2039 clarified and tightened (Section 8). It is noted that "text" and 2040 "message" are valid media types for use with SDP, but that "control" 2041 and "data" are under-specified and deprecated. 2043 RFC 2119 terms are now used throughout to specify requirements 2044 levels. Certain of those requirements, in particular in relation to 2045 parameter registration, are stricter than those in RFC 2327. 2047 The "RTP/SAVP" RTP profile and its "fmt" namespace are registered. 2049 The attributes "a=inactive" and "a=maxptime" have been added. 2051 RFC 2327 mandated that either "e=" or "p=" was required. Both are 2052 now optional, to reflect actual usage. 2054 The significant limitations of the "k=" field are noted, and its use 2055 is deprecated. 2057 Most uses of the "x-" prefix notation for experimental parameters are 2058 disallowed and the other uses are deprecated. 2060 11. Acknowledgements 2062 Many people in the IETF Multiparty Multimedia Session Control 2063 (MMUSIC) working group have made comments and suggestions 2064 contributing to this document. In particular, we would like to thank 2065 Eve Schooler, Steve Casner, Bill Fenner, Allison Mankin, Ross 2066 Finlayson, Peter Parnes, Joerg Ott, Carsten Bormann, Steve Hanna, 2067 Jonathan Lennox, Keith Drage, Sean Olson, Bernie Hoeneisen and 2068 Jonathan Rosenberg. 2070 12. References 2072 12.1 Normative References 2074 [1] Mockapetris, P., "Domain names - concepts and facilities", 2075 STD 13, RFC 1034, November 1987. 2077 [2] Mockapetris, P., "Domain names - implementation and 2078 specification", STD 13, RFC 1035, November 1987. 2080 [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement 2081 Levels", BCP 14, RFC 2119, March 1997. 2083 [4] Crocker, D. and P. Overell, "Augmented BNF for Syntax 2084 Specifications: ABNF", RFC 2234, November 1997. 2086 [5] Yergeau, F., "UTF-8, a transformation format of ISO 10646", 2087 RFC 2279, January 1998. 2089 [6] Handley, M. and V. Jacobson, "SDP: Session Description 2090 Protocol", RFC 2327, April 1998. 2092 [7] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 2093 Resource Identifiers (URI): Generic Syntax", RFC 2396, 2094 August 1998. 2096 [8] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA 2097 Considerations Section in RFCs", BCP 26, RFC 2434, 2098 October 1998. 2100 [9] Hinden, R., Carpenter, B., and L. Masinter, "Format for Literal 2101 IPv6 Addresses in URL's", RFC 2732, December 1999. 2103 [10] Alvestrand, H., "Tags for the Identification of Languages", 2104 BCP 47, RFC 3066, January 2001. 2106 [11] Faltstrom, P., Hoffman, P., and A. Costello, 2107 "Internationalizing Domain Names in Applications (IDNA)", 2108 RFC 3490, March 2003. 2110 [12] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", 2111 RFC 3548, July 2003. 2113 12.2 Informative References 2115 [13] Mills, D., "Network Time Protocol (Version 3) Specification, 2116 Implementation", RFC 1305, March 1992. 2118 [14] Handley, M., Perkins, C., and E. Whelan, "Session Announcement 2119 Protocol", RFC 2974, October 2000. 2121 [15] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., 2122 Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: 2123 Session Initiation Protocol", RFC 3261, June 2002. 2125 [16] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming 2126 Protocol (RTSP)", RFC 2326, April 1998. 2128 [17] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with 2129 Session Description Protocol (SDP)", RFC 3264, June 2002. 2131 [18] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, 2132 "RTP: A Transport Protocol for Real-Time Applications", STD 64, 2133 RFC 3550, July 2003. 2135 [19] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video 2136 Conferences with Minimal Control", STD 65, RFC 3551, July 2003. 2138 [20] Casner, S., "Session Description Protocol (SDP) Bandwidth 2139 Modifiers for RTP Control Protocol (RTCP) Bandwidth", RFC 3556, 2140 July 2003. 2142 [21] Huitema, C., "Real Time Control Protocol (RTCP) attribute in 2143 Session Description Protocol (SDP)", RFC 3605, October 2003. 2145 [22] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 2146 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 2147 RFC 3711, March 2004. 2149 [23] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating 2150 User Agent Capabilities in the Session Initiation Protocol 2151 (SIP)", RFC 3840, August 2004. 2153 [24] Westerlund, M., "A Transport Independent Bandwidth Modifier for 2154 the Session Description Protocol (SDP)", RFC 3890, 2155 September 2004. 2157 [25] International Telecommunications Union, "H.323 extended for 2158 loosely coupled conferences", ITU Recommendation H.332, 2159 September 1998. 2161 [26] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K. 2162 Norrman, "Key Management Extensions for Session Description 2163 Protocol (SDP) and Real Time Streaming Protocol (RTSP)", 2164 draft-ietf-mmusic-kmgmt-ext-12 (work in progress), 2165 November 2004. 2167 [27] Andreasen, F., Baugher, M., and D. Wing, "Session Description 2168 Protocol Security Descriptions for Media Streams", 2169 draft-ietf-mmusic-sdescriptions-07 (work in progress), 2170 July 2004. 2172 Authors' Addresses 2174 Mark Handley 2175 University College London 2176 Department of Computer Science 2177 Gower Street 2178 London WC1E 6BT 2179 UK 2181 Email: M.Handley@cs.ucl.ac.uk 2183 Van Jacobson 2184 Packet Design 2185 2465 Latham Street 2186 Mountain View, CA 94040 2187 USA 2189 Email: van@packetdesign.com 2191 Colin Perkins 2192 University of Glasgow 2193 Department of Computing Science 2194 17 Lilybank Gardens 2195 Glasgow G12 8QQ 2196 UK 2198 Email: csp@csperkins.org 2200 Intellectual Property Statement 2202 The IETF takes no position regarding the validity or scope of any 2203 Intellectual Property Rights or other rights that might be claimed to 2204 pertain to the implementation or use of the technology described in 2205 this document or the extent to which any license under such rights 2206 might or might not be available; nor does it represent that it has 2207 made any independent effort to identify any such rights. 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