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'I-D.alvestrand-dispatch-rtcweb-datagram') == Outdated reference: A later version (-16) exists of draft-ietf-codec-opus-05 == Outdated reference: A later version (-17) exists of draft-ietf-hybi-thewebsocketprotocol-07 ** Downref: Normative reference to an Experimental draft: draft-westin-payload-vp8 (ref. 'I-D.westin-payload-vp8') ** Obsolete normative reference: RFC 1890 (Obsoleted by RFC 3551) Summary: 3 errors (**), 0 flaws (~~), 12 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group H. Alvestrand 3 Internet-Draft Google 4 Intended status: Standards Track June 20, 2011 5 Expires: December 22, 2011 7 Overview: Real Time Protocols for Brower-based Applications 8 draft-alvestrand-rtcweb-overview-01 10 Abstract 12 This document gives an overview and context of a protocol suite 13 intended for use with real-time applications that can be deployed in 14 browsers - "real time communication on the Web". 16 It intends to serve as a starting and coordination point to make sure 17 all the parts that are needed to achieve this goal are findable, and 18 that the parts that belong in the Internet protocol suite are fully 19 specified and on the right publication track. 21 This work is an attempt to synthesize the input of many people, but 22 makes no claims to fully represent the views of any of them. All 23 parts of the document should be regarded as open for discussion, 24 unless the RTCWEB chairs have declared consensus on an item. 26 This document is a candidate to become a work item of the RTCWEB 27 working group. 29 Requirements Language 31 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 32 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 33 document are to be interpreted as described in RFC 2119 [RFC2119]. 35 Status of this Memo 37 This Internet-Draft is submitted in full conformance with the 38 provisions of BCP 78 and BCP 79. 40 Internet-Drafts are working documents of the Internet Engineering 41 Task Force (IETF). Note that other groups may also distribute 42 working documents as Internet-Drafts. The list of current Internet- 43 Drafts is at http://datatracker.ietf.org/drafts/current/. 45 Internet-Drafts are draft documents valid for a maximum of six months 46 and may be updated, replaced, or obsoleted by other documents at any 47 time. It is inappropriate to use Internet-Drafts as reference 48 material or to cite them other than as "work in progress." 49 This Internet-Draft will expire on December 22, 2011. 51 Copyright Notice 53 Copyright (c) 2011 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents 58 (http://trustee.ietf.org/license-info) in effect on the date of 59 publication of this document. Please review these documents 60 carefully, as they describe your rights and restrictions with respect 61 to this document. Code Components extracted from this document must 62 include Simplified BSD License text as described in Section 4.e of 63 the Trust Legal Provisions and are provided without warranty as 64 described in the Simplified BSD License. 66 Table of Contents 68 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 69 2. Principles and Terminology . . . . . . . . . . . . . . . . . . 5 70 2.1. Goals of this document . . . . . . . . . . . . . . . . . . 5 71 2.2. Relationship between API and protocol . . . . . . . . . . 5 72 2.3. On interoperability and innovation . . . . . . . . . . . . 6 73 2.4. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7 74 3. Functionality groups . . . . . . . . . . . . . . . . . . . . . 7 75 4. Data transport . . . . . . . . . . . . . . . . . . . . . . . . 9 76 5. Data framing and securing . . . . . . . . . . . . . . . . . . 9 77 6. Data formats . . . . . . . . . . . . . . . . . . . . . . . . . 9 78 7. Connection management . . . . . . . . . . . . . . . . . . . . 9 79 8. Presentation and control . . . . . . . . . . . . . . . . . . . 10 80 9. Local system support functions . . . . . . . . . . . . . . . . 10 81 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 82 11. Security Considerations . . . . . . . . . . . . . . . . . . . 11 83 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 84 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 85 13.1. Normative References . . . . . . . . . . . . . . . . . . . 12 86 13.2. Informative References . . . . . . . . . . . . . . . . . . 13 87 Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 13 88 A.1. Changes from 89 draft-alvestrand-dispatch-rtcweb-datagram-00 to -01 . . . 13 90 A.2. Changes from draft-alvestrand-dispatch-01 to 91 draft-alvestrand-rtcweb-overview-00 . . . . . . . . . . . 13 92 A.3. Changes from draft-alvestrand-rtcweb-00 to -01 . . . . . . 14 93 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14 95 1. Introduction 97 The Internet was, from very early in its lifetime, considered a 98 possible vehicle for the deployment of real-time, interactive 99 applications - with the most easily imaginable being audio 100 conversations (aka "Internet telephony") and videoconferencing. 102 The first attempts to build this were dependent on special networks, 103 special hardware and custom-built software, often at very high prices 104 or at low quality, placing great demands on the infrastructure. 106 As the available bandwidth has increased, and as processors and other 107 hardware has become ever faster, the barriers to participation have 108 decreased, and it is possible to deliver a satisfactory experience on 109 commonly available computing hardware. 111 Still, there are a number of barriers to the ability to communicate 112 universally - one of these is that there is, as of yet, no single set 113 of communication protocols that all agree should be made available 114 for communication; another is the sheer lack of universal 115 identification systems (such as is served by telephone numbers or 116 email addresses in other communications systems). 118 Development of The Universal Solution has proved hard, however, for 119 all the usual reasons. This memo aims to take a more building-block- 120 oriented approach, and try to find consensus on a set of substrate 121 components that we think will be useful in any real-time 122 communications systems. 124 The last few years have also seen a new platform rise for deployment 125 of services: The browser-embedded application, or "Web application". 126 It turns out that as long as the browser platform has the necessary 127 interfaces, it is possible to deliver almost any kind of service on 128 it. 130 Traditionally, these interfaces have been delivered by plugins, which 131 had to be downloaded and installed separately from the browser; in 132 the development of HTML5, much promise is seen by the possibility of 133 making those interfaces available in a standardized way within the 134 browser. 136 This memo specifies a set of building blocks that can be made 137 accessible and controllable through a Javascript API interface in a 138 browser, and which together form a necessary and sufficient set of 139 functions to allow the use of interactive audio and video in 140 applications that communicate directly between browsers across the 141 Internet. 143 Other efforts, for instance the W3C WebRTC, Web Applications and 144 Device API working groups, focus on making standardized APIs and 145 interfaces available, within or alongside the HTML5 effort, for those 146 functions; this memo concentrates on specifying the protocols and 147 subprotocols that are needed to specify the interactions that happen 148 across the network. 150 2. Principles and Terminology 152 2.1. Goals of this document 154 The goal of the RTCWEB protocol specification is to specify a set of 155 protocols that, if all are implemented, will allow the implementation 156 to communicate with another implementation using audio, video and 157 auxiliary data sent along the most direct possible path between the 158 participants. 160 This document is intended to serve as the roadmap to the RTCWEB 161 specifications. It defines terms used by other pieces of 162 specification, lists references to other specifications that don't 163 need further elaboration in the RTCWEB context, and gives pointers to 164 other documents that form part of the RTCWEB suite. 166 By reading this document and the documents it refers to, it should be 167 possible to have all information needed to implement an RTCWEB 168 compatible implementation. 170 2.2. Relationship between API and protocol 172 The total RTCWEB/WEBRTC effort consists of two pieces: 174 o A protocol specification, done in the IETF 176 o A Javascript API specification, done in the W3C 178 Together, these two specifications aim to provide an environment 179 where Javascript embedded in any page, viewed in any compatible 180 browser, when suitably authorized by its user, is able to set up 181 communication using audio, video and auxiliary data, where the 182 browser environment does not constrain the types of application in 183 which this functionality can be used. 185 The protocol specification does not assume that all implementations 186 implement this API; it is not intended to be possible by observing 187 the bits on the wire whether they come from a browser or from another 188 device implementing this specification. 190 The goal of cooperation between the protocol specification and the 191 API specification is that for all options and features of the 192 protocol specification, it should be clear which API calls to make to 193 exercise that option or feature; similarly, for any sequence of API 194 calls, it should be clear which protocol options and features will be 195 invoked. Both subject to constraints of the implementation, of 196 course. 198 2.3. On interoperability and innovation 200 The "Mission statement of the IETF" [RFC3935] states that "The 201 benefit of a standard to the Internet is in interoperability - that 202 multiple products implementing a standard are able to work together 203 in order to deliver valuable functions to the Internet's users." 205 Communication on the Internet frequently occurs in two phases: 207 o Two parties communicate, through some mechanism, what 208 functionality they both are able to support 210 o They use that shared communicative functionality to communicate, 211 or, failing to find anything in common, give up on communication. 213 There are often many choices that can be made for communicative 214 functionality; the history of the Internet is rife with the proposal, 215 standardization, implementation, and success or failure of many types 216 of options, in all sorts of protocols. 218 The goal of having a mandatory to implement function set is to 219 prevent negotiation failure, not to preempt or prevent negotiation. 221 The presence of a mandatory to implement function set serves as a 222 strong changer of the marketplace of deployment - in that it gives a 223 guarantee that, as long as you conform to a specification, and the 224 other party is willing to accept communication at the base level of 225 that specification, you can communicate successfully. 227 The alternative - that of having no mandatory to implement - does not 228 mean that you cannot communicate, it merely means that in order to be 229 part of the communications partnership, you have to implement the 230 standard "and then some" - that "and then some" usually being called 231 a profile of some sort; in the version most antithetical to the 232 Internet ethos, that "and then some" consists of having to use a 233 specific vendor's product only. 235 2.4. Terminology 237 The following terms are used in this document, and as far as possible 238 across the documents specifying the RTCWEB suite, in the specific 239 meanings given here. Other terms are used in their commonly used 240 meaning. 242 The list is in alphabetical order. 244 API: Application Programming Interface - a specification of a set of 245 calls and events, usually tied to a programming language or an 246 abstract formal specification such as WebIDL, with its defined 247 semantics. 249 Interactive: Communication between multiple parties, where the 250 expectation is that an action from one party can cause a reaction 251 by another party, and the reaction can be observed by the first 252 party, with the total time required for the action/reaction/ 253 observation is on the order of no more than hundreds of 254 milliseconds. 256 Media: Audio and video content. Not to be confused with 257 "transmission media" such as wires. 259 Protocol: A specification of a set of data units, their 260 representation, and rules for their transmission, with their 261 defined semantics. A protocol is usually thought of as going 262 between systems. 264 Real-time media: Media where generation of content and display of 265 content are intended to occur closely together in time (on the 266 order of no more than hundreds of milliseconds). 268 NOTE: Where common definitions exist for these terms, those 269 definitions should be used to the greatest extent possible. 271 TODO: Extend this list with other terms that might prove slippery. 273 3. Functionality groups 275 The functionality groups that are needed can be specified, more or 276 less from the bottom up, as: 278 o Data transport: TCP, UDP and the means to securely set up 279 connections between entities, as well as the functions for 280 deciding when to send data: Congestion management, bandwidth 281 estimation and so on. 283 o Data framing: RTP and other data formats that serve as containers, 284 and their functions for data confidentiality and integrity. 286 o Data formats: Codec specifications, format specifications and 287 functionality specifications for the data passed between systems. 288 Audio and video codecs, as well as formats for data and document 289 sharing, belong in this category. In order to make use of data 290 formats, a way to describe them, a session description, is needed. 292 o Connection management: Setting up connections, agreeing on data 293 formats, changing data formats during the duration of a call; SIP 294 and Jingle/XMPP belong in this category. 296 o Presentation and control: What needs to happen in order to ensure 297 that interactions behave in a non-surprising manner. This can 298 include floor control, screen layout, voice activated image 299 switching and other such functions - where part of the system 300 require the cooperation between parties. Cisco/Tandberg's TIP was 301 one attempt at specifying this functionality. 303 o Local system support functions: These are things that need not be 304 specified uniformly, because each participant may choose to do 305 these in a way of the participant's choosing, without affecting 306 the bits on the wire in a way that others have to be cognizant of. 307 Examples in this category include echo cancellation (some forms of 308 it), local authentication and authorization mechanisms, OS access 309 control and the ability to do local recording of conversations. 311 Within each functionality group, it is important to preserve both 312 freedom to innovate and the ability for global communication. 313 Freedom to innovate is helped by doing the specification in terms of 314 interfaces, not implementation; any implementation able to 315 communicate according to the interfaces is a valid implementation. 316 Ability to communicate globally is helped both by having core 317 specifications be unencumbered by IPR issues and by having the 318 formats and protocols be fully enough specified to allow for 319 independent implementation. 321 One can think of the three first groups as forming a "media transport 322 infrastructure", and of the three last groups as forming a "media 323 service". In many contexts, it makes sense to use a common 324 specification for the media transport infrastructure, which can be 325 embedded in browsers and accessed using standard interfaces, and "let 326 a thousand flowers bloom" in the "media service" layer; to achieve 327 interoperable services, however, at least the first five of the six 328 groups need to be specified. 330 4. Data transport 332 Data transport refers to the sending and receiving of data over the 333 network interfaces, the choice of network-layer addresses at each end 334 of the communication, and the interaction with any intermediate 335 entities that handle the data, but do not modify it (such as TURN 336 relays). 338 It includes necessary functions for congestion control: When not to 339 send data. 341 The data transport protocols used by RTCWEB are described in . 344 The interactions with intermediate boxes, such as firewalls, relays 345 and NAT boxes, is described in . 348 5. Data framing and securing 350 SRTP [RFC3550] is used for transport of all real-time media. 352 The detailed considerations for usage of functions from RTP and SRTP, 353 as well as for non-media real-time data, are given in . 356 6. Data formats 358 The intent of this specification is to allow each communications 359 event to use the data formats that are best suited for that 360 particular instance, where a format is supported by both sides of the 361 connection. However, a minimum standard is greatly helpful in order 362 to ensure that communication can be achieved. This document 363 specifies a minimum baseline that will be supported by all 364 implementations of this specification, and leaves further codecs to 365 be included at the will of the implementor. 367 The mandatory to implement codecs, as well as any profiling 368 requirements for both mandatory and optional codecs, is described in 369 . 371 7. Connection management 373 The methods, mechanisms and requirements for setting up, negotiating 374 and tearing down connections is a large subject, and one where it is 375 desirable to have both interoperability and freedom to innovate. 377 The particular choices made for RTCWEB are described in . 380 8. Presentation and control 382 The most important part of control is the user's control over the 383 browser's interaction with input/output devices and communications 384 channels. It is important that the user have some way of figuring 385 out where his audio, video or texting is being sent, for what 386 purported reason, and what guarantees are made by the parties that 387 form part of this control channel. This is largely a local function 388 between the browser, the underlying operating system and the user 389 interface; this is being worked on as part of the W3C API effort. 390 392 9. Local system support functions 394 These are characterized by the fact that the quality of these 395 functions strongly influences the user experience, but the exact 396 algorithm does not need coordination. In some cases (for instance 397 echo cancellation, as described below), the overall system definition 398 may need to specify that the overall system needs to have some 399 characteristics for which these facilities are useful, without 400 requiring them to be implemented a certain way. 402 Local functions include echo cancellation, volume control, camera 403 management including focus, zoom, pan/tilt controls (if available), 404 and more. 406 Certain parts of the system SHOULD conform to certain properties, for 407 instance: 409 o Echo cancellation should be good enough that feedback (defined as 410 a rising volume of sound with no local sound input) does not 411 occur. 413 o Privacy concerns must be satisfied; for instance, if remote 414 control of camera is offered, the APIs should be available to let 415 the local participant to figure out who's controlling the camera, 416 and possibly decide to revoke the permission for camera usage. 418 o Automatic gain control, if present, should normalize a speaking 419 voice into 422 o 424 The requirements on RTCWEB systems in this category are found in 425 . 427 10. IANA Considerations 429 This document makes no request of IANA. 431 Note to RFC Editor: this section may be removed on publication as an 432 RFC. 434 11. Security Considerations 436 Security of the web-enabled real time communications comes in several 437 pieces: 439 o Security of the components: The browsers, and other servers 440 involved. The most target-rich environment here is probably the 441 browser; the aim here should be that the introduction of these 442 components introduces no additional vulnerability. 444 o Security of the communication channels: It should be easy for a 445 participant to reassure himself of the security of his 446 communication - by verifying the crypto parameters of the links he 447 himself participates in, and to get reassurances from the other 448 parties to the communication that they promise that appropriate 449 measures are taken. 451 o Security of the partners' identity: verifying that the 452 participants are who they say they are (when positive 453 identification is appropriate), or that their identity cannot be 454 uncovered (when anonymity is a goal of the application). 456 The security analysis, and the requirements derived from that 457 analysis, is contained in . 459 12. Acknowledgements 461 The number of people who have taken part in the discussions 462 surroounding this draft are too numerous to list, or even to 463 identify. The ones below have made special, identifiable 464 contributions; this does not mean that others' contributions are less 465 important. 467 Thanks to Cary Bran, Cullen Jennings, Colin Perkins, Magnus 468 Westerlund and Joerg Ott, who offered techincal contributions on 469 various versions of the draft. 471 Thanks to Justin Uberti and Simon Leinen for document review. 473 13. References 475 13.1. Normative References 477 [I-D.alvestrand-dispatch-rtcweb-datagram] 478 Alvestrand, H., "A Datagram Transport for the RTC-Web 479 profile", draft-alvestrand-dispatch-rtcweb-datagram-01 480 (work in progress), February 2011. 482 [I-D.ietf-codec-opus] 483 Valin, J. and K. Vos, "Definition of the Opus Audio 484 Codec", draft-ietf-codec-opus-05 (work in progress), 485 March 2011. 487 [I-D.ietf-hybi-thewebsocketprotocol] 488 Fette, I., "The WebSocket protocol", 489 draft-ietf-hybi-thewebsocketprotocol-07 (work in 490 progress), April 2011. 492 [I-D.westin-payload-vp8] 493 Westin, P. and H. Lundin, "Proposal for the IETF on "RTP 494 Payload Format for VP8 Video"", 495 draft-westin-payload-vp8-02 (work in progress), 496 March 2011. 498 [RFC1890] Schulzrinne, H., "RTP Profile for Audio and Video 499 Conferences with Minimal Control", RFC 1890, January 1996. 501 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 502 Requirement Levels", BCP 14, RFC 2119, March 1997. 504 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 505 Jacobson, "RTP: A Transport Protocol for Real-Time 506 Applications", STD 64, RFC 3550, July 2003. 508 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 509 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 510 RFC 3711, March 2004. 512 [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 513 "Extended RTP Profile for Real-time Transport Control 514 Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, 515 July 2006. 517 [RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for 518 Real-time Transport Control Protocol (RTCP)-Based Feedback 519 (RTP/SAVPF)", RFC 5124, February 2008. 521 13.2. Informative References 523 [I-D.ietf-avt-rtp-svc] 524 Wenger, S., Wang, Y., Schierl, T., and A. Eleftheriadis, 525 "RTP Payload Format for Scalable Video Coding", 526 draft-ietf-avt-rtp-svc-27 (work in progress), 527 February 2011. 529 [RFC3935] Alvestrand, H., "A Mission Statement for the IETF", 530 BCP 95, RFC 3935, October 2004. 532 Appendix A. Change log 534 This section may be deleted by the RFC Editor when preparing for 535 publication. 537 A.1. Changes from draft-alvestrand-dispatch-rtcweb-datagram-00 to -01 539 Added section "On interoperability and innovation" 541 Added data confidentiality and integrity to the "data framing" layer 543 Added congestion management requirements in the "data transport" 544 layer section 546 Changed need for non-media data from "question: do we need this?" to 547 "Open issue: How do we do this?" 549 Strengthened disclaimer that listed codecs are placeholders, not 550 decisions. 552 More details on why the "local system support functions" section is 553 there. 555 A.2. Changes from draft-alvestrand-dispatch-01 to 556 draft-alvestrand-rtcweb-overview-00 558 Added section on "Relationship between API and protocol" 560 Added terminology section 561 Mentioned congestion management as part of the "data transport" layer 562 in the layer list 564 A.3. Changes from draft-alvestrand-rtcweb-00 to -01 566 Removed most technical content, and replaced with pointers to drafts 567 as requested and identified by the RTCWEB WG chairs. 569 Added content to acknowledgements section. 571 Added change log. 573 Spell-checked document. 575 Author's Address 577 Harald T. Alvestrand 578 Google 579 Kungsbron 2 580 Stockholm, 11122 581 Sweden 583 Email: harald@alvestrand.no