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'15') (Obsoleted by RFC 8856) Summary: 8 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 BFCPbis Working Group T. Kristensen, Ed. 3 Internet-Draft Cisco 4 Obsoletes: 4583 (if approved) G. Camarillo 5 Intended status: Standards Track Ericsson 6 Expires: September 6, 2012 March 5, 2012 8 Session Description Protocol (SDP) Format for Binary Floor Control 9 Protocol (BFCP) Streams 10 draft-ietf-bfcpbis-rfc4583bis-00 12 Abstract 14 This document specifies how to describe Binary Floor Control Protocol 15 (BFCP) streams in Session Description Protocol (SDP) descriptions. 16 User agents using the offer/answer model to establish BFCP streams 17 use this format in their offers and answers. 19 This document obsoletes RFC 4583. Changes from RFC 4583 are 20 summarized in section 15. 22 Status of this Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on September 6, 2012. 39 Copyright Notice 41 Copyright (c) 2012 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 This document may contain material from IETF Documents or IETF 55 Contributions published or made publicly available before November 56 10, 2008. The person(s) controlling the copyright in some of this 57 material may not have granted the IETF Trust the right to allow 58 modifications of such material outside the IETF Standards Process. 59 Without obtaining an adequate license from the person(s) controlling 60 the copyright in such materials, this document may not be modified 61 outside the IETF Standards Process, and derivative works of it may 62 not be created outside the IETF Standards Process, except to format 63 it for publication as an RFC or to translate it into languages other 64 than English. 66 Table of Contents 68 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 69 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 70 3. Fields in the 'm' Line . . . . . . . . . . . . . . . . . . . . 4 71 4. Floor Control Server Determination . . . . . . . . . . . . . . 5 72 5. The 'confid' and 'userid' SDP Attributes . . . . . . . . . . . 7 73 6. Association between Streams and Floors . . . . . . . . . . . . 7 74 7. TCP Connection Management . . . . . . . . . . . . . . . . . . 8 75 8. Authentication . . . . . . . . . . . . . . . . . . . . . . . . 8 76 9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 77 10. Security Considerations . . . . . . . . . . . . . . . . . . . 10 78 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 79 11.1. Registration of SDP 'proto' Values . . . . . . . . . . . 10 80 11.2. Registration of the SDP 'floorctrl' Attribute . . . . . . 11 81 11.3. Registration of the SDP 'confid' Attribute . . . . . . . 11 82 11.4. Registration of the SDP 'userid' Attribute . . . . . . . 11 83 11.5. Registration of the SDP 'floorid' Attribute . . . . . . . 12 84 12. Changes from RFC 4583 . . . . . . . . . . . . . . . . . . . . 12 85 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 86 14. Normative References . . . . . . . . . . . . . . . . . . . . . 13 87 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 89 1. Introduction 91 As discussed in the BFCP (Binary Floor Control Protocol) 92 specification [8], a given BFCP client needs a set of data in order 93 to establish a BFCP connection to a floor control server. These data 94 include the transport address of the server, the conference 95 identifier, and the user identifier. 97 One way for clients to obtain this information is to use an offer/ 98 answer [4] exchange. This document specifies how to encode this 99 information in the SDP session descriptions that are part of such an 100 offer/answer exchange. 102 User agents typically use the offer/answer model to establish a 103 number of media streams of different types. Following this model, a 104 BFCP connection is described as any other media stream by using an 105 SDP 'm' line, possibly followed by a number of attributes encoded in 106 'a' lines. 108 2. Terminology 110 In this document, the key words "MUST", "MUST NOT", "REQUIRED", 111 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT 112 RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as 113 described in BCP 14, RFC 2119 [1] and indicate requirement levels for 114 compliant implementations. 116 3. Fields in the 'm' Line 118 This section describes how to generate an 'm' line for a BFCP stream. 120 According to the SDP specification [11], the 'm' line format is the 121 following: 123 m= ... 125 The media field MUST have a value of "application". 127 The port field is set following the rules in [7]. Depending on the 128 value of the 'setup' attribute (discussed in Section 7), the port 129 field contains the port to which the remote endpoint will direct BFCP 130 messages or is irrelevant (i.e., the endpoint will initiate the 131 connection towards the remote endpoint) and should be set to a value 132 of 9, which is the discard port. A port field value of zero has the 133 standard SDP meaning (i.e., rejection of the media stream). 135 We define four new values for the transport field: TCP/BFCP, TCP/TLS/ 136 BFCP, UDP/BFCP, and UDP/TLS/BFCP. TCP/BFCP is used when BFCP runs 137 directly on top of TCP, TCP/TLS/BFCP is used when BFCP runs on top of 138 TLS, which in turn runs on top of TCP. Similarly, UDP/BFCP is used 139 when BFCP runs directly on top of UDP, and UDP/TLS/BFCP is used when 140 BFCP runs on top of DTLS [12], which in turn runs on top of UDP. 142 The fmt (format) list is ignored for BFCP. The fmt list of BFCP 'm' 143 lines SHOULD contain a single "*" character. 145 The following is an example of an 'm' line for a BFCP connection: 147 m=application 50000 TCP/TLS/BFCP * 149 4. Floor Control Server Determination 151 When two endpoints establish a BFCP stream, they need to determine 152 which of them acts as a floor control server. In the most common 153 scenario, a client establishes a BFCP stream with a conference server 154 that acts as the floor control server. Floor control server 155 determination is straight forward because one endpoint can only act 156 as a client and the other can only act as a floor control server. 158 However, there are scenarios where both endpoints could act as a 159 floor control server. For example, in a two-party session that 160 involves an audio stream and a shared whiteboard, the endpoints need 161 to decide which party will be acting as the floor control server. 163 Furthermore, there are situations where both the offerer and the 164 answerer act as both clients and floor control servers in the same 165 session. For example, in a two-party session that involves an audio 166 stream and a shared whiteboard, one party acts as the floor control 167 server for the audio stream and the other acts as the floor control 168 server for the shared whiteboard. 170 We define the 'floorctrl' SDP media-level attribute to perform floor 171 control determination. Its Augmented BNF syntax [2] is: 173 floor-control-attribute = "a=floorctrl:" role *(SP role) 174 role = "c-only" / "s-only" / "c-s" 176 The offerer includes this attribute to state all the roles it would 177 be willing to perform: 179 c-only: The offerer would be willing to act as a floor control 180 client only. 182 s-only: The offerer would be willing to act as a floor control 183 server only. 185 c-s: The offerer would be willing to act both as a floor control 186 client and as a floor control server. 188 If an SDP media description in an offer contains a 'floorctrl' 189 attribute, the answerer accepting that media MUST include one in the 190 corresponding media description of the answer. The answerer includes 191 this attribute to state which role the answerer will perform. That 192 is, the answerer chooses one of the roles the offerer is willing to 193 perform and generates an answer with the corresponding role for the 194 answerer. Table 1 shows the corresponding roles for an answerer, 195 depending on the offerer's role. 197 +---------+----------+ 198 | Offerer | Answerer | 199 +---------+----------+ 200 | c-only | s-only | 201 | s-only | c-only | 202 | c-s | c-s | 203 +---------+----------+ 205 Table 1: Roles 207 The following are the descriptions of the roles when they are chosen 208 by an answerer: 210 c-only: The answerer will act as a floor control client. 211 Consequently, the offerer will act as a floor control server. 213 s-only: The answerer will act as a floor control server. 214 Consequently, the offerer will act as a floor control client. 216 c-s: The answerer will act both as a floor control client and as a 217 floor control server. Consequently, the offerer will also act 218 both as a floor control client and as a floor control server. 220 Endpoints that use the offer/answer model to establish BFCP 221 connections MUST support the 'floorctrl' attribute. A floor control 222 server acting as an offerer or as an answerer SHOULD include this 223 attribute in its session descriptions. 225 If the 'floorctrl' attribute is not used in an offer/answer exchange, 226 by default the offerer and the answerer will act as a floor control 227 client and as a floor control server, respectively. 229 The following is an example of a 'floorctrl' attribute in an offer. 230 When this attribute appears in an answer, it only carries one role: 232 a=floorctrl:c-only s-only c-s 234 5. The 'confid' and 'userid' SDP Attributes 236 We define the 'confid' and the 'userid' SDP media-level attributes. 237 These attributes are used by a floor control server to provide a 238 client with a conference ID and a user ID, respectively. Their 239 Augmented BNF syntax [2] is: 241 confid-attribute = "a=confid:" conference-id 242 conference-id = token 243 userid-attribute = "a=userid:" user-id 244 user-id = token 246 The 'confid' and the 'userid' attributes carry the integer 247 representation of a conference ID and a user ID, respectively. 249 Endpoints that use the offer/answer model to establish BFCP 250 connections MUST support the 'confid' and the 'userid' attributes. A 251 floor control server acting as an offerer or as an answerer SHOULD 252 include these attributes in its session descriptions. 254 6. Association between Streams and Floors 256 We define the 'floorid' SDP media-level attribute. Its Augmented BNF 257 syntax [2] is: 259 floor-id-attribute = "a=floorid:" token [" mstrm:" token *(SP token)] 261 The 'floorid' attribute is used in the SDP media description for BFCP 262 media. It defines a floor identifier and, possibly, associates it 263 with one or more media streams. The token representing the floor ID 264 is the integer representation of the Floor ID to be used in BFCP. 265 The token representing the media stream is a pointer to the media 266 stream, which is identified by an SDP label attribute [9]. 268 Endpoints that use the offer/answer model to establish BFCP 269 connections MUST support the 'floorid' and the 'label' attributes. A 270 floor control server acting as an offerer or as an answerer SHOULD 271 include these attributes in its session descriptions. 273 7. TCP Connection Management 275 The management of the TCP connection used to transport BFCP is 276 performed using the 'setup' and 'connection' attributes, as defined 277 in [7]. 279 The 'setup' attribute indicates which of the endpoints (client or 280 floor control server) initiates the TCP connection. The 'connection' 281 attribute handles TCP connection reestablishment. 283 The BFCP specification [8] describes a number of situations when the 284 TCP connection between a client and the floor control server needs to 285 be reestablished. However, that specification does not describe the 286 reestablishment process because this process depends on how the 287 connection was established in the first place. BFCP entities using 288 the offer/answer model follow the following rules. 290 When the existing TCP connection is reset following the rules in [8], 291 the client SHOULD generate an offer towards the floor control server 292 in order to reestablish the connection. If a TCP connection cannot 293 deliver a BFCP message and times out, the entity that attempted to 294 send the message (i.e., the one that detected the TCP timeout) SHOULD 295 generate an offer in order to reestablish the TCP connection. 297 Endpoints that use the offer/answer model to establish BFCP 298 connections MUST support the 'setup' and 'connection' attributes. 300 8. Authentication 302 When a BFCP connection is established using the offer/answer model, 303 it is assumed that the offerer and the answerer authenticate each 304 other using some mechanism. Once this mutual authentication takes 305 place, all the offerer and the answerer need to ensure is that the 306 entity they are receiving BFCP messages from is the same as the one 307 that generated the previous offer or answer. 309 When SIP is used to perform an offer/answer exchange, the initial 310 mutual authentication takes place at the SIP level. Additionally, 311 SIP uses S/MIME [6] to provide an integrity-protected channel with 312 optional confidentiality for the offer/answer exchange. BFCP takes 313 advantage of this integrity-protected offer/answer exchange to 314 perform authentication. Within the offer/answer exchange, the 315 offerer and answerer exchange the fingerprints of their self-signed 316 certificates. These self-signed certificates are then used to 317 establish the TLS connection that will carry BFCP traffic between the 318 offerer and the answerer. 320 BFCP clients and floor control servers follow the rules in [10] 321 regarding certificate choice and presentation. This implies that 322 unless a 'fingerprint' attribute is included in the session 323 description, the certificate provided at the TLS-level MUST either be 324 directly signed by one of the other party's trust anchors or be 325 validated using a certification path that terminates at one of the 326 other party's trust anchors [5]. Endpoints that use the offer/answer 327 model to establish BFCP connections MUST support the 'fingerprint' 328 attribute and SHOULD include it in their session descriptions. 330 When TLS is used with TCP, once the underlying connection is 331 established, the answerer acts as the TLS server regardless of its 332 role (passive or active) in the TCP establishment procedure. 334 9. Examples 336 For the purpose of brevity, the main portion of the session 337 description is omitted in the examples, which only show 'm' lines and 338 their attributes. 340 The following is an example of an offer sent by a conference server 341 to a client. 343 m=application 50000 TCP/TLS/BFCP * 344 a=setup:passive 345 a=connection:new 346 a=fingerprint:SHA-1 \ 347 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 348 a=floorctrl:s-only 349 a=confid:4321 350 a=userid:1234 351 a=floorid:1 mstrm:10 352 a=floorid:2 mstrm:11 353 m=audio 50002 RTP/AVP 0 354 a=label:10 355 m=video 50004 RTP/AVP 31 356 a=label:11 358 Note that due to RFC formatting conventions, this document splits SDP 359 across lines whose content would exceed 72 characters. A backslash 360 character marks where this line folding has taken place. This 361 backslash and its trailing CRLF and whitespace would not appear in 362 actual SDP content. 364 The following is the answer returned by the client. 366 m=application 9 TCP/TLS/BFCP * 367 a=setup:active 368 a=connection:new 369 a=fingerprint:SHA-1 \ 370 3D:B4:7B:E3:CC:FC:0D:1B:5D:31:33:9E:48:9B:67:FE:68:40:E8:21 371 a=floorctrl:c-only 372 m=audio 55000 RTP/AVP 0 373 m=video 55002 RTP/AVP 31 375 10. Security Considerations 377 The BFCP [8], SDP [11], and offer/answer [4] specifications discuss 378 security issues related to BFCP, SDP, and offer/answer, respectively. 379 In addition, [7] and [10] discuss security issues related to the 380 establishment of TCP and TLS connections using an offer/answer model. 381 Furthermore, when using DTLS over UDP, considerations for its use 382 with RTP and RTCP are presented in [13]. The requirements for the 383 offer/answer exchange, as listed in Section 5 of that document, MUST 384 be followed. 386 BFCP assumes that an initial integrity-protected channel is used to 387 exchange self-signed certificates between a client and the floor 388 control server. For session descriptions carried in SIP [3], S/MIME 389 [6] is the natural choice to provide such a channel. 391 11. IANA Considerations 393 Editorial note: The changes in Section 11.1 instruct the IANA to 394 perform a set of actions, the rest is as in [14]. 396 11.1. Registration of SDP 'proto' Values 398 This section instructs the IANA to register the two new values UDP/ 399 BFCP and UDP/TLS/BFCP for the SDP 'proto' field under the Session 400 Description Protocol (SDP) Parameters registry, in addition to the 401 two already registered for [14]: 403 +--------------+-----------+ 404 | Value | Reference | 405 +--------------+-----------+ 406 | TCP/BFCP | RFCxxxx | 407 | TCP/TLS/BFCP | RFCxxxx | 408 | UDP/BFCP | RFCxxxx | 409 | UDP/TLS/BFCP | RFCxxxx | 410 +--------------+-----------+ 412 Table 2: Values for the SDP 'proto' field 414 11.2. Registration of the SDP 'floorctrl' Attribute 416 The IANA has registered the following SDP att-field under the Session 417 Description Protocol (SDP) Parameters registry: 419 Contact name: Gonzalo.Camarillo@ericsson.com 421 Attribute name: floorctrl 423 Long-form attribute name: Floor Control 425 Type of attribute: Media level 427 Subject to charset: No 429 Purpose of attribute: The 'floorctrl' attribute is used to perform 430 floor control server determination. 432 Allowed attribute values: 1*("c-only" / "s-only" / "c-s") 434 11.3. Registration of the SDP 'confid' Attribute 436 The IANA has registered the following SDP att-field under the Session 437 Description Protocol (SDP) Parameters registry: 439 Contact name: Gonzalo.Camarillo@ericsson.com 441 Attribute name: confid 443 Long-form attribute name: Conference Identifier 445 Type of attribute: Media level 447 Subject to charset: No 449 Purpose of attribute: The 'confid' attribute carries the integer 450 representation of a Conference ID. 452 Allowed attribute values: A token 454 11.4. Registration of the SDP 'userid' Attribute 456 The IANA has registered the following SDP att-field under the Session 457 Description Protocol (SDP) Parameters registry: 459 Contact name: Gonzalo.Camarillo@ericsson.com 461 Attribute name: userid 463 Long-form attribute name: User Identifier 465 Type of attribute: Media level 467 Subject to charset: No 469 Purpose of attribute: The 'userid' attribute carries the integer 470 representation of a User ID. 472 Allowed attribute values: A token 474 11.5. Registration of the SDP 'floorid' Attribute 476 The IANA has registered the following SDP att-field under the Session 477 Description Protocol (SDP) Parameters registry: 479 Contact name: Gonzalo.Camarillo@ericsson.com 481 Attribute name: floorid 483 Long-form attribute name: Floor Identifier 485 Type of attribute: Media level 487 Subject to charset: No 489 Purpose of attribute: The 'floorid' attribute associates a floor 490 with one or more media streams. 492 Allowed attribute values: Tokens 494 12. Changes from RFC 4583 496 Following is the list of technical changes and bug fixes from [15]. 498 Main purpose of this work was to add signaling support necessary to 499 support BFCP over unreliable transport, as described in [8]. The 500 section number to which updates apply are indicated in parentheses 501 below: 503 Fields in the 'm' Line (Section 3) The section is re-written to 504 remove reference to the exclusivity of TCP as a transport for BFCP 505 streams. The transport field values UDP/BFCP and UDP/TLS/BFCP 506 added. 508 Authentication (8) In last paragraph, made clear that a TCP 509 connection was described. 511 Security Considerations (Section 10) For the DTLS over UDP case, 512 mention existing considerations and requirements for the offer/ 513 answer exchange in [13]. 515 Registration of SDP 'proto' Values (Section 11.1) Register the two 516 new values UDP/BFCP and UDP/TLS/BFCP in the SDP parameters 517 registry. 519 The bug fixes from [15]: 521 Errata ID: 712 (Section 4) (Section 6) Language clarification. 522 Don't use terms like an SDP attribute is "used in an 'm' line", 523 instead make clear that the attribute is a media-level attribute. 525 Fix typo in example (Section 9) Do not use 'm-stream' in the SDP 526 example, use the correct 'mstrm' as specified in Section 9. 528 13. Acknowledgements 530 Joerg Ott, Keith Drage, Alan Johnston, Eric Rescorla, Roni Even, and 531 Oscar Novo provided useful ideas for the original [15]. As well as, 532 Geir Arne Sandbakken, Charles Eckel, Eoin McLeod and Mark Thompson 533 for this document. 535 14. Normative References 537 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 538 Levels", BCP 14, RFC 2119, March 1997. 540 [2] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 541 Specifications: ABNF", RFC 4234, October 2005. 543 [3] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., 544 Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: 545 Session Initiation Protocol", RFC 3261, June 2002. 547 [4] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with 548 Session Description Protocol (SDP)", RFC 3264, June 2002. 550 [5] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509 551 Public Key Infrastructure Certificate and Certificate 552 Revocation List (CRL) Profile", RFC 3280, April 2002. 554 [6] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions 555 (S/MIME) Version 3.1 Certificate Handling", RFC 3850, 556 July 2004. 558 [7] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the 559 Session Description Protocol (SDP)", RFC 4145, September 2005. 561 [8] Kristensen, T., Eckel, C., Heggestad, A., and G. Sandbakken, 562 "Revision of the Binary Floor Control Protocol (BFCP) for use 563 over an unreliable transport", draft-ietf-bfcpbis-rfc4582bis-01 564 (work in progress), February 2012. 566 [9] Levin, O. and G. Camarillo, "The Session Description Protocol 567 (SDP) Label Attribute", RFC 4574, August 2006. 569 [10] Lennox, J., "Connection-Oriented Media Transport over the 570 Transport Layer Security (TLS) Protocol in the Session 571 Description Protocol (SDP)", RFC 4572, July 2006. 573 [11] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 574 Description Protocol", RFC 4566, July 2006. 576 [12] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 577 Security", RFC 4347, April 2006. 579 [13] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework for 580 Establishing a Secure Real-time Transport Protocol (SRTP) 581 Security Context Using Datagram Transport Layer Security 582 (DTLS)", RFC 5763, May 2010. 584 [14] Camarillo, G., Ott, J., and K. Drage, "The Binary Floor Control 585 Protocol (BFCP)", RFC 4582, November 2006. 587 [15] Camarillo, G., "Session Description Protocol (SDP) Format for 588 Binary Floor Control Protocol (BFCP) Streams", RFC 4583, 589 November 2006. 591 Authors' Addresses 593 Tom Kristensen (editor) 594 Cisco 595 Philip Pedersens vei 22 596 N-1366 Lysaker 597 Norway 599 Email: tomkrist@cisco.com, tomkri@ifi.uio.no 601 Gonzalo Camarillo 602 Ericsson 603 Hirsalantie 11 604 Jorvas 02420 605 Finland 607 Email: Gonzalo.Camarillo@ericsson.com