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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Obsolete informational reference (is this intentional?): RFC 5245 (Obsoleted by RFC 8445, RFC 8839) Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 2 comments (--). 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 August 24, 2011 5 Expires: February 25, 2012 7 Overview: Real Time Protocols for Brower-based Applications 8 draft-ietf-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 February 25, 2012. 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. Architecture and Functionality groups . . . . . . . . . . . . 8 75 4. Data transport . . . . . . . . . . . . . . . . . . . . . . . . 12 76 5. Data framing and securing . . . . . . . . . . . . . . . . . . 12 77 6. Data formats . . . . . . . . . . . . . . . . . . . . . . . . . 12 78 7. Connection management . . . . . . . . . . . . . . . . . . . . 12 79 8. Presentation and control . . . . . . . . . . . . . . . . . . . 13 80 9. Local system support functions . . . . . . . . . . . . . . . . 13 81 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 82 11. Security Considerations . . . . . . . . . . . . . . . . . . . 14 83 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 84 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 85 13.1. Normative References . . . . . . . . . . . . . . . . . . . 15 86 13.2. Informative References . . . . . . . . . . . . . . . . . . 15 87 Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 15 88 A.1. Changes from 89 draft-alvestrand-dispatch-rtcweb-datagram-00 to -01 . . . 16 90 A.2. Changes from draft-alvestrand-dispatch-01 to 91 draft-alvestrand-rtcweb-overview-00 . . . . . . . . . . . 16 92 A.3. Changes from draft-alvestrand-rtcweb-00 to -01 . . . . . . 16 93 A.4. Changes from draft-alvestrand-rtcweb-overview-01 to 94 draft-ietf-rtcweb-overview-00 . . . . . . . . . . . . . . 16 95 A.5. Changes from draft-ietf-rtcweb-overview -00 to -01 . . . . 17 96 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 17 98 1. Introduction 100 The Internet was, from very early in its lifetime, considered a 101 possible vehicle for the deployment of real-time, interactive 102 applications - with the most easily imaginable being audio 103 conversations (aka "Internet telephony") and videoconferencing. 105 The first attempts to build this were dependent on special networks, 106 special hardware and custom-built software, often at very high prices 107 or at low quality, placing great demands on the infrastructure. 109 As the available bandwidth has increased, and as processors and other 110 hardware has become ever faster, the barriers to participation have 111 decreased, and it is possible to deliver a satisfactory experience on 112 commonly available computing hardware. 114 Still, there are a number of barriers to the ability to communicate 115 universally - one of these is that there is, as of yet, no single set 116 of communication protocols that all agree should be made available 117 for communication; another is the sheer lack of universal 118 identification systems (such as is served by telephone numbers or 119 email addresses in other communications systems). 121 Development of The Universal Solution has proved hard, however, for 122 all the usual reasons. This memo aims to take a more building-block- 123 oriented approach, and try to find consensus on a set of substrate 124 components that we think will be useful in any real-time 125 communications systems. 127 The last few years have also seen a new platform rise for deployment 128 of services: The browser-embedded application, or "Web application". 129 It turns out that as long as the browser platform has the necessary 130 interfaces, it is possible to deliver almost any kind of service on 131 it. 133 Traditionally, these interfaces have been delivered by plugins, which 134 had to be downloaded and installed separately from the browser; in 135 the development of HTML5, much promise is seen by the possibility of 136 making those interfaces available in a standardized way within the 137 browser. 139 This memo specifies a set of building blocks that can be made 140 accessible and controllable through a Javascript API interface in a 141 browser, and which together form a necessary and sufficient set of 142 functions to allow the use of interactive audio and video in 143 applications that communicate directly between browsers across the 144 Internet. 146 Other efforts, for instance the W3C WebRTC, Web Applications and 147 Device API working groups, focus on making standardized APIs and 148 interfaces available, within or alongside the HTML5 effort, for those 149 functions; this memo concentrates on specifying the protocols and 150 subprotocols that are needed to specify the interactions that happen 151 across the network. 153 2. Principles and Terminology 155 2.1. Goals of this document 157 The goal of the RTCWEB protocol specification is to specify a set of 158 protocols that, if all are implemented, will allow the implementation 159 to communicate with another implementation using audio, video and 160 auxiliary data sent along the most direct possible path between the 161 participants. 163 This document is intended to serve as the roadmap to the RTCWEB 164 specifications. It defines terms used by other pieces of 165 specification, lists references to other specifications that don't 166 need further elaboration in the RTCWEB context, and gives pointers to 167 other documents that form part of the RTCWEB suite. 169 By reading this document and the documents it refers to, it should be 170 possible to have all information needed to implement an RTCWEB 171 compatible implementation. 173 2.2. Relationship between API and protocol 175 The total RTCWEB/WEBRTC effort consists of two pieces: 177 o A protocol specification, done in the IETF 179 o A Javascript API specification, done in the W3C [webrtc-api] 181 Together, these two specifications aim to provide an environment 182 where Javascript embedded in any page, viewed in any compatible 183 browser, when suitably authorized by its user, is able to set up 184 communication using audio, video and auxiliary data, where the 185 browser environment does not constrain the types of application in 186 which this functionality can be used. 188 The protocol specification does not assume that all implementations 189 implement this API; it is not intended to be possible by observing 190 the bits on the wire whether they come from a browser or from another 191 device implementing this specification. 193 The goal of cooperation between the protocol specification and the 194 API specification is that for all options and features of the 195 protocol specification, it should be clear which API calls to make to 196 exercise that option or feature; similarly, for any sequence of API 197 calls, it should be clear which protocol options and features will be 198 invoked. Both subject to constraints of the implementation, of 199 course. 201 2.3. On interoperability and innovation 203 The "Mission statement of the IETF" [RFC3935] states that "The 204 benefit of a standard to the Internet is in interoperability - that 205 multiple products implementing a standard are able to work together 206 in order to deliver valuable functions to the Internet's users." 208 Communication on the Internet frequently occurs in two phases: 210 o Two parties communicate, through some mechanism, what 211 functionality they both are able to support 213 o They use that shared communicative functionality to communicate, 214 or, failing to find anything in common, give up on communication. 216 There are often many choices that can be made for communicative 217 functionality; the history of the Internet is rife with the proposal, 218 standardization, implementation, and success or failure of many types 219 of options, in all sorts of protocols. 221 The goal of having a mandatory to implement function set is to 222 prevent negotiation failure, not to preempt or prevent negotiation. 224 The presence of a mandatory to implement function set serves as a 225 strong changer of the marketplace of deployment - in that it gives a 226 guarantee that, as long as you conform to a specification, and the 227 other party is willing to accept communication at the base level of 228 that specification, you can communicate successfully. 230 The alternative - that of having no mandatory to implement - does not 231 mean that you cannot communicate, it merely means that in order to be 232 part of the communications partnership, you have to implement the 233 standard "and then some" - that "and then some" usually being called 234 a profile of some sort; in the version most antithetical to the 235 Internet ethos, that "and then some" consists of having to use a 236 specific vendor's product only. 238 2.4. Terminology 240 The following terms are used in this document, and as far as possible 241 across the documents specifying the RTCWEB suite, in the specific 242 meanings given here. Not all terms are used in this document. Other 243 terms are used in their commonly used meaning. 245 The list is in alphabetical order. 247 Agent: Undefined term. See "SDP Agent" and "ICE Agent". 249 API: Application Programming Interface - a specification of a set of 250 calls and events, usually tied to a programming language or an 251 abstract formal specification such as WebIDL, with its defined 252 semantics. 254 ICE Agent: An implementation of the ICE [RFC5245] protocol. An ICE 255 Agent may also be an SDP Agent, but there exist ICE Agents that do 256 not use SDP (for instance those that use Jingle). 258 Interactive: Communication between multiple parties, where the 259 expectation is that an action from one party can cause a reaction 260 by another party, and the reaction can be observed by the first 261 party, with the total time required for the action/reaction/ 262 observation is on the order of no more than hundreds of 263 milliseconds. 265 Media: Audio and video content. Not to be confused with 266 "transmission media" such as wires. 268 Media path: The path that media data follows from one browser to 269 another. 271 Protocol: A specification of a set of data units, their 272 representation, and rules for their transmission, with their 273 defined semantics. A protocol is usually thought of as going 274 between systems. 276 Real-time media: Media where generation of content and display of 277 content are intended to occur closely together in time (on the 278 order of no more than hundreds of milliseconds). 280 SDP Agent: The protocol implementation involved in the SDP offer/ 281 answer exchange, as defined in [RFC3264] section 3. 283 Signaling: Communication that happens in order to establish, manage 284 and control media paths. 286 Signaling Path: The communication channels used between entities 287 participating in signalling to transfer signaling. There may be 288 more entities in the signaling path than in the media path. 290 NOTE: Where common definitions exist for these terms, those 291 definitions should be used to the greatest extent possible. 293 TODO: Extend this list with other terms that might prove slippery. 295 3. Architecture and Functionality groups 297 The model of real-time support for browser-based applications does 298 not envisage that the browser will contain all the functions that 299 need to be performed in order to have a function such as a telephone 300 or a videoconferencing unit; the vision is that the browser will have 301 the functions that are needed for a Web application, working in 302 conjunction with its backend servers, to implement these functions. 304 This means that two vital interfaces need specification: The 305 protocols that browsers talk to each other, without any intervening 306 servers, and the APIs that are offered for a Javascript application 307 to take advantage of the browser's functionality. 309 +------------------------+ On-the-wire 310 | | Protocols 311 | Servers |---------> 312 | | 313 | | 314 +------------------------+ 315 ^ 316 | 317 | 318 | HTTP/ 319 | Websockets 320 | 321 | 322 +----------------------------+ 323 | Javascript/HTML/CSS | 324 +----------------------------+ 325 Other ^ ^RTC 326 APIs | |APIs 327 +---|-----------------|------+ 328 | | | | 329 | +---------+| 330 | | Browser || On-the-wire 331 | Browser | RTC || Protocols 332 | | Function|-----------> 333 | | || 334 | | || 335 | +---------+| 336 +---------------------|------+ 337 | 338 V 339 Native OS Services 341 Figure 1: Browser Model 343 As for all protocol and API specifications, there is no restriction 344 that the protocols can only be used to talk to another browser; since 345 they are fully specified, any device that implements the protocols 346 faithfully should be able to interoperate with the application 347 running in the browser. 349 A commonly imagined model of deployment is the one depicted below. 351 +-----------+ +-----------+ 352 | Web | | Web | 353 | | Signalling | | 354 | |-------------| | 355 | Server | path | Server | 356 | | | | 357 +-----------+ +-----------+ 358 / \ 359 / \ Proprietary over 360 / \ HTTP/Websockets 361 / \ 362 / Proprietary over \ 363 / HTTP/Websockets \ 364 / \ 365 +-----------+ +-----------+ 366 |JS/HTML/CSS| |JS/HTML/CSS| 367 +-----------+ +-----------+ 368 +-----------+ +-----------+ 369 | | | | 370 | | | | 371 | Browser | ------------------------- | Browser | 372 | | Media path | | 373 | | | | 374 +-----------+ +-----------+ 376 Figure 2: Browser RTC Trapezoid 378 If the two Web servers are operated by different entities, the 379 signalling path needs to be standardized too; for example, both 380 servers might implement SIP, and the servers would talk SIP to each 381 other, and each would translate between the SIP protocol and their 382 proprietary representation for sending to their application running 383 in the browser. 385 On this sketch, the critical part to note is that the media path 386 ("low path") goes directly between the browsers, so it has to be 387 conformant to the specifications of the RTCWEB protocol suite; the 388 signalling path ("high path") goes via servers that can modify, 389 translate or massage the signals as needed. 391 The functionality groups that are needed in the browser can be 392 specified, more or less from the bottom up, as: 394 o Data transport: TCP, UDP and the means to securely set up 395 connections between entities, as well as the functions for 396 deciding when to send data: Congestion management, bandwidth 397 estimation and so on. 399 o Data framing: RTP and other data formats that serve as containers, 400 and their functions for data confidentiality and integrity. 402 o Data formats: Codec specifications, format specifications and 403 functionality specifications for the data passed between systems. 404 Audio and video codecs, as well as formats for data and document 405 sharing, belong in this category. In order to make use of data 406 formats, a way to describe them, a session description, is needed. 408 o Connection management: Setting up connections, agreeing on data 409 formats, changing data formats during the duration of a call; SIP 410 and Jingle/XMPP belong in this category. 412 o Presentation and control: What needs to happen in order to ensure 413 that interactions behave in a non-surprising manner. This can 414 include floor control, screen layout, voice activated image 415 switching and other such functions - where part of the system 416 require the cooperation between parties. Cisco/Tandberg's TIP was 417 one attempt at specifying this functionality. 419 o Local system support functions: These are things that need not be 420 specified uniformly, because each participant may choose to do 421 these in a way of the participant's choosing, without affecting 422 the bits on the wire in a way that others have to be cognizant of. 423 Examples in this category include echo cancellation (some forms of 424 it), local authentication and authorization mechanisms, OS access 425 control and the ability to do local recording of conversations. 427 Within each functionality group, it is important to preserve both 428 freedom to innovate and the ability for global communication. 429 Freedom to innovate is helped by doing the specification in terms of 430 interfaces, not implementation; any implementation able to 431 communicate according to the interfaces is a valid implementation. 432 Ability to communicate globally is helped both by having core 433 specifications be unencumbered by IPR issues and by having the 434 formats and protocols be fully enough specified to allow for 435 independent implementation. 437 One can think of the three first groups as forming a "media transport 438 infrastructure", and of the three last groups as forming a "media 439 service". In many contexts, it makes sense to use a common 440 specification for the media transport infrastructure, which can be 441 embedded in browsers and accessed using standard interfaces, and "let 442 a thousand flowers bloom" in the "media service" layer; to achieve 443 interoperable services, however, at least the first five of the six 444 groups need to be specified. 446 4. Data transport 448 Data transport refers to the sending and receiving of data over the 449 network interfaces, the choice of network-layer addresses at each end 450 of the communication, and the interaction with any intermediate 451 entities that handle the data, but do not modify it (such as TURN 452 relays). 454 It includes necessary functions for congestion control: When not to 455 send data. 457 The data transport protocols used by RTCWEB are described in . 460 The interactions with intermediate boxes, such as firewalls, relays 461 and NAT boxes, is described in . 464 5. Data framing and securing 466 SRTP [RFC3550] is used for transport of all real-time media. 468 The detailed considerations for usage of functions from RTP and SRTP, 469 as well as for non-media real-time data, are given in . 472 6. Data formats 474 The intent of this specification is to allow each communications 475 event to use the data formats that are best suited for that 476 particular instance, where a format is supported by both sides of the 477 connection. However, a minimum standard is greatly helpful in order 478 to ensure that communication can be achieved. This document 479 specifies a minimum baseline that will be supported by all 480 implementations of this specification, and leaves further codecs to 481 be included at the will of the implementor. 483 The mandatory to implement codecs, as well as any profiling 484 requirements for both mandatory and optional codecs, is described in 485 . 487 7. Connection management 489 The methods, mechanisms and requirements for setting up, negotiating 490 and tearing down connections is a large subject, and one where it is 491 desirable to have both interoperability and freedom to innovate. 493 The particular choices made for RTCWEB are described in . 496 8. Presentation and control 498 The most important part of control is the user's control over the 499 browser's interaction with input/output devices and communications 500 channels. It is important that the user have some way of figuring 501 out where his audio, video or texting is being sent, for what 502 purported reason, and what guarantees are made by the parties that 503 form part of this control channel. This is largely a local function 504 between the browser, the underlying operating system and the user 505 interface; this is being worked on as part of the W3C API effort. 506 508 9. Local system support functions 510 These are characterized by the fact that the quality of these 511 functions strongly influences the user experience, but the exact 512 algorithm does not need coordination. In some cases (for instance 513 echo cancellation, as described below), the overall system definition 514 may need to specify that the overall system needs to have some 515 characteristics for which these facilities are useful, without 516 requiring them to be implemented a certain way. 518 Local functions include echo cancellation, volume control, camera 519 management including focus, zoom, pan/tilt controls (if available), 520 and more. 522 Certain parts of the system SHOULD conform to certain properties, for 523 instance: 525 o Echo cancellation should be good enough to achieve the suppression 526 of acoustical feedback loops below a perceptually noticeable 527 level. 529 o Privacy concerns must be satisfied; for instance, if remote 530 control of camera is offered, the APIs should be available to let 531 the local participant to figure out who's controlling the camera, 532 and possibly decide to revoke the permission for camera usage. 534 o Automatic gain control, if present, should normalize a speaking 535 voice into 538 The requirements on RTCWEB systems in this category are found in 539 . 541 10. IANA Considerations 543 This document makes no request of IANA. 545 Note to RFC Editor: this section may be removed on publication as an 546 RFC. 548 11. Security Considerations 550 Security of the web-enabled real time communications comes in several 551 pieces: 553 o Security of the components: The browsers, and other servers 554 involved. The most target-rich environment here is probably the 555 browser; the aim here should be that the introduction of these 556 components introduces no additional vulnerability. 558 o Security of the communication channels: It should be easy for a 559 participant to reassure himself of the security of his 560 communication - by verifying the crypto parameters of the links he 561 himself participates in, and to get reassurances from the other 562 parties to the communication that they promise that appropriate 563 measures are taken. 565 o Security of the partners' identity: verifying that the 566 participants are who they say they are (when positive 567 identification is appropriate), or that their identity cannot be 568 uncovered (when anonymity is a goal of the application). 570 The security analysis, and the requirements derived from that 571 analysis, is contained in . 573 12. Acknowledgements 575 The number of people who have taken part in the discussions 576 surrounding this draft are too numerous to list, or even to identify. 577 The ones below have made special, identifiable contributions; this 578 does not mean that others' contributions are less important. 580 Thanks to Cary Bran, Cullen Jennings, Colin Perkins, Magnus 581 Westerlund and Joerg Ott, who offered technical contributions on 582 various versions of the draft. 584 Thanks to Jonathan Rosenberg, Matthew Kaufman and others at Skype for 585 the draft I lifted the ASCII drawings from. 587 Thanks to Justin Uberti and Simon Leinen for document review. 589 13. References 591 13.1. Normative References 593 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 594 Requirement Levels", BCP 14, RFC 2119, March 1997. 596 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 597 Jacobson, "RTP: A Transport Protocol for Real-Time 598 Applications", STD 64, RFC 3550, July 2003. 600 13.2. Informative References 602 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 603 with Session Description Protocol (SDP)", RFC 3264, 604 June 2002. 606 [RFC3935] Alvestrand, H., "A Mission Statement for the IETF", 607 BCP 95, RFC 3935, October 2004. 609 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 610 (ICE): A Protocol for Network Address Translator (NAT) 611 Traversal for Offer/Answer Protocols", RFC 5245, 612 April 2010. 614 [webrtc-api] 615 Bergkvist, Burnett, Jennings, Narayanan, "WebRTC 1.0: 616 Real-time Communication Between Browsers", August 2011. 618 Available at 619 http://dev.w3.org/2011/webrtc/editor/webrtc.html 621 Appendix A. Change log 623 This section may be deleted by the RFC Editor when preparing for 624 publication. 626 A.1. Changes from draft-alvestrand-dispatch-rtcweb-datagram-00 to -01 628 Added section "On interoperability and innovation" 630 Added data confidentiality and integrity to the "data framing" layer 632 Added congestion management requirements in the "data transport" 633 layer section 635 Changed need for non-media data from "question: do we need this?" to 636 "Open issue: How do we do this?" 638 Strengthened disclaimer that listed codecs are placeholders, not 639 decisions. 641 More details on why the "local system support functions" section is 642 there. 644 A.2. Changes from draft-alvestrand-dispatch-01 to 645 draft-alvestrand-rtcweb-overview-00 647 Added section on "Relationship between API and protocol" 649 Added terminology section 651 Mentioned congestion management as part of the "data transport" layer 652 in the layer list 654 A.3. Changes from draft-alvestrand-rtcweb-00 to -01 656 Removed most technical content, and replaced with pointers to drafts 657 as requested and identified by the RTCWEB WG chairs. 659 Added content to acknowledgements section. 661 Added change log. 663 Spell-checked document. 665 A.4. Changes from draft-alvestrand-rtcweb-overview-01 to 666 draft-ietf-rtcweb-overview-00 668 Changed draft name and document date. 670 Removed unused references 672 A.5. Changes from draft-ietf-rtcweb-overview -00 to -01 674 Added architecture figures to section 2. 676 Changed the description of "echo cancellation" under "local system 677 support functions". 679 Added a few more definitions. 681 Author's Address 683 Harald T. Alvestrand 684 Google 685 Kungsbron 2 686 Stockholm, 11122 687 Sweden 689 Email: harald@alvestrand.no