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Alvestrand 3 Internet-Draft Google 4 Intended status: Standards Track July 1, 2011 5 Expires: January 2, 2012 7 Overview: Real Time Protocols for Brower-based Applications 8 draft-ietf-rtcweb-overview-00 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 January 2, 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. 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 . . . . . . . . . . . . . . . . . . 12 87 Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 12 88 A.1. Changes from 89 draft-alvestrand-dispatch-rtcweb-datagram-00 to -01 . . . 12 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 . . . . . . 13 93 A.4. Changes from draft-alvestrand-rtcweb-overview-01 to 94 draft-ietf-rtcweb-overview-00 . . . . . . . . . . . . . . 13 95 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13 97 1. Introduction 99 The Internet was, from very early in its lifetime, considered a 100 possible vehicle for the deployment of real-time, interactive 101 applications - with the most easily imaginable being audio 102 conversations (aka "Internet telephony") and videoconferencing. 104 The first attempts to build this were dependent on special networks, 105 special hardware and custom-built software, often at very high prices 106 or at low quality, placing great demands on the infrastructure. 108 As the available bandwidth has increased, and as processors and other 109 hardware has become ever faster, the barriers to participation have 110 decreased, and it is possible to deliver a satisfactory experience on 111 commonly available computing hardware. 113 Still, there are a number of barriers to the ability to communicate 114 universally - one of these is that there is, as of yet, no single set 115 of communication protocols that all agree should be made available 116 for communication; another is the sheer lack of universal 117 identification systems (such as is served by telephone numbers or 118 email addresses in other communications systems). 120 Development of The Universal Solution has proved hard, however, for 121 all the usual reasons. This memo aims to take a more building-block- 122 oriented approach, and try to find consensus on a set of substrate 123 components that we think will be useful in any real-time 124 communications systems. 126 The last few years have also seen a new platform rise for deployment 127 of services: The browser-embedded application, or "Web application". 128 It turns out that as long as the browser platform has the necessary 129 interfaces, it is possible to deliver almost any kind of service on 130 it. 132 Traditionally, these interfaces have been delivered by plugins, which 133 had to be downloaded and installed separately from the browser; in 134 the development of HTML5, much promise is seen by the possibility of 135 making those interfaces available in a standardized way within the 136 browser. 138 This memo specifies a set of building blocks that can be made 139 accessible and controllable through a Javascript API interface in a 140 browser, and which together form a necessary and sufficient set of 141 functions to allow the use of interactive audio and video in 142 applications that communicate directly between browsers across the 143 Internet. 145 Other efforts, for instance the W3C WebRTC, Web Applications and 146 Device API working groups, focus on making standardized APIs and 147 interfaces available, within or alongside the HTML5 effort, for those 148 functions; this memo concentrates on specifying the protocols and 149 subprotocols that are needed to specify the interactions that happen 150 across the network. 152 2. Principles and Terminology 154 2.1. Goals of this document 156 The goal of the RTCWEB protocol specification is to specify a set of 157 protocols that, if all are implemented, will allow the implementation 158 to communicate with another implementation using audio, video and 159 auxiliary data sent along the most direct possible path between the 160 participants. 162 This document is intended to serve as the roadmap to the RTCWEB 163 specifications. It defines terms used by other pieces of 164 specification, lists references to other specifications that don't 165 need further elaboration in the RTCWEB context, and gives pointers to 166 other documents that form part of the RTCWEB suite. 168 By reading this document and the documents it refers to, it should be 169 possible to have all information needed to implement an RTCWEB 170 compatible implementation. 172 2.2. Relationship between API and protocol 174 The total RTCWEB/WEBRTC effort consists of two pieces: 176 o A protocol specification, done in the IETF 178 o A Javascript API specification, done in the W3C 180 Together, these two specifications aim to provide an environment 181 where Javascript embedded in any page, viewed in any compatible 182 browser, when suitably authorized by its user, is able to set up 183 communication using audio, video and auxiliary data, where the 184 browser environment does not constrain the types of application in 185 which this functionality can be used. 187 The protocol specification does not assume that all implementations 188 implement this API; it is not intended to be possible by observing 189 the bits on the wire whether they come from a browser or from another 190 device implementing this specification. 192 The goal of cooperation between the protocol specification and the 193 API specification is that for all options and features of the 194 protocol specification, it should be clear which API calls to make to 195 exercise that option or feature; similarly, for any sequence of API 196 calls, it should be clear which protocol options and features will be 197 invoked. Both subject to constraints of the implementation, of 198 course. 200 2.3. On interoperability and innovation 202 The "Mission statement of the IETF" [RFC3935] states that "The 203 benefit of a standard to the Internet is in interoperability - that 204 multiple products implementing a standard are able to work together 205 in order to deliver valuable functions to the Internet's users." 207 Communication on the Internet frequently occurs in two phases: 209 o Two parties communicate, through some mechanism, what 210 functionality they both are able to support 212 o They use that shared communicative functionality to communicate, 213 or, failing to find anything in common, give up on communication. 215 There are often many choices that can be made for communicative 216 functionality; the history of the Internet is rife with the proposal, 217 standardization, implementation, and success or failure of many types 218 of options, in all sorts of protocols. 220 The goal of having a mandatory to implement function set is to 221 prevent negotiation failure, not to preempt or prevent negotiation. 223 The presence of a mandatory to implement function set serves as a 224 strong changer of the marketplace of deployment - in that it gives a 225 guarantee that, as long as you conform to a specification, and the 226 other party is willing to accept communication at the base level of 227 that specification, you can communicate successfully. 229 The alternative - that of having no mandatory to implement - does not 230 mean that you cannot communicate, it merely means that in order to be 231 part of the communications partnership, you have to implement the 232 standard "and then some" - that "and then some" usually being called 233 a profile of some sort; in the version most antithetical to the 234 Internet ethos, that "and then some" consists of having to use a 235 specific vendor's product only. 237 2.4. Terminology 239 The following terms are used in this document, and as far as possible 240 across the documents specifying the RTCWEB suite, in the specific 241 meanings given here. Other terms are used in their commonly used 242 meaning. 244 The list is in alphabetical order. 246 API: Application Programming Interface - a specification of a set of 247 calls and events, usually tied to a programming language or an 248 abstract formal specification such as WebIDL, with its defined 249 semantics. 251 Interactive: Communication between multiple parties, where the 252 expectation is that an action from one party can cause a reaction 253 by another party, and the reaction can be observed by the first 254 party, with the total time required for the action/reaction/ 255 observation is on the order of no more than hundreds of 256 milliseconds. 258 Media: Audio and video content. Not to be confused with 259 "transmission media" such as wires. 261 Protocol: A specification of a set of data units, their 262 representation, and rules for their transmission, with their 263 defined semantics. A protocol is usually thought of as going 264 between systems. 266 Real-time media: Media where generation of content and display of 267 content are intended to occur closely together in time (on the 268 order of no more than hundreds of milliseconds). 270 NOTE: Where common definitions exist for these terms, those 271 definitions should be used to the greatest extent possible. 273 TODO: Extend this list with other terms that might prove slippery. 275 3. Functionality groups 277 The functionality groups that are needed can be specified, more or 278 less from the bottom up, as: 280 o Data transport: TCP, UDP and the means to securely set up 281 connections between entities, as well as the functions for 282 deciding when to send data: Congestion management, bandwidth 283 estimation and so on. 285 o Data framing: RTP and other data formats that serve as containers, 286 and their functions for data confidentiality and integrity. 288 o Data formats: Codec specifications, format specifications and 289 functionality specifications for the data passed between systems. 290 Audio and video codecs, as well as formats for data and document 291 sharing, belong in this category. In order to make use of data 292 formats, a way to describe them, a session description, is needed. 294 o Connection management: Setting up connections, agreeing on data 295 formats, changing data formats during the duration of a call; SIP 296 and Jingle/XMPP belong in this category. 298 o Presentation and control: What needs to happen in order to ensure 299 that interactions behave in a non-surprising manner. This can 300 include floor control, screen layout, voice activated image 301 switching and other such functions - where part of the system 302 require the cooperation between parties. Cisco/Tandberg's TIP was 303 one attempt at specifying this functionality. 305 o Local system support functions: These are things that need not be 306 specified uniformly, because each participant may choose to do 307 these in a way of the participant's choosing, without affecting 308 the bits on the wire in a way that others have to be cognizant of. 309 Examples in this category include echo cancellation (some forms of 310 it), local authentication and authorization mechanisms, OS access 311 control and the ability to do local recording of conversations. 313 Within each functionality group, it is important to preserve both 314 freedom to innovate and the ability for global communication. 315 Freedom to innovate is helped by doing the specification in terms of 316 interfaces, not implementation; any implementation able to 317 communicate according to the interfaces is a valid implementation. 318 Ability to communicate globally is helped both by having core 319 specifications be unencumbered by IPR issues and by having the 320 formats and protocols be fully enough specified to allow for 321 independent implementation. 323 One can think of the three first groups as forming a "media transport 324 infrastructure", and of the three last groups as forming a "media 325 service". In many contexts, it makes sense to use a common 326 specification for the media transport infrastructure, which can be 327 embedded in browsers and accessed using standard interfaces, and "let 328 a thousand flowers bloom" in the "media service" layer; to achieve 329 interoperable services, however, at least the first five of the six 330 groups need to be specified. 332 4. Data transport 334 Data transport refers to the sending and receiving of data over the 335 network interfaces, the choice of network-layer addresses at each end 336 of the communication, and the interaction with any intermediate 337 entities that handle the data, but do not modify it (such as TURN 338 relays). 340 It includes necessary functions for congestion control: When not to 341 send data. 343 The data transport protocols used by RTCWEB are described in . 346 The interactions with intermediate boxes, such as firewalls, relays 347 and NAT boxes, is described in . 350 5. Data framing and securing 352 SRTP [RFC3550] is used for transport of all real-time media. 354 The detailed considerations for usage of functions from RTP and SRTP, 355 as well as for non-media real-time data, are given in . 358 6. Data formats 360 The intent of this specification is to allow each communications 361 event to use the data formats that are best suited for that 362 particular instance, where a format is supported by both sides of the 363 connection. However, a minimum standard is greatly helpful in order 364 to ensure that communication can be achieved. This document 365 specifies a minimum baseline that will be supported by all 366 implementations of this specification, and leaves further codecs to 367 be included at the will of the implementor. 369 The mandatory to implement codecs, as well as any profiling 370 requirements for both mandatory and optional codecs, is described in 371 . 373 7. Connection management 375 The methods, mechanisms and requirements for setting up, negotiating 376 and tearing down connections is a large subject, and one where it is 377 desirable to have both interoperability and freedom to innovate. 379 The particular choices made for RTCWEB are described in . 382 8. Presentation and control 384 The most important part of control is the user's control over the 385 browser's interaction with input/output devices and communications 386 channels. It is important that the user have some way of figuring 387 out where his audio, video or texting is being sent, for what 388 purported reason, and what guarantees are made by the parties that 389 form part of this control channel. This is largely a local function 390 between the browser, the underlying operating system and the user 391 interface; this is being worked on as part of the W3C API effort. 392 394 9. Local system support functions 396 These are characterized by the fact that the quality of these 397 functions strongly influences the user experience, but the exact 398 algorithm does not need coordination. In some cases (for instance 399 echo cancellation, as described below), the overall system definition 400 may need to specify that the overall system needs to have some 401 characteristics for which these facilities are useful, without 402 requiring them to be implemented a certain way. 404 Local functions include echo cancellation, volume control, camera 405 management including focus, zoom, pan/tilt controls (if available), 406 and more. 408 Certain parts of the system SHOULD conform to certain properties, for 409 instance: 411 o Echo cancellation should be good enough that feedback (defined as 412 a rising volume of sound with no local sound input) does not 413 occur. 415 o Privacy concerns must be satisfied; for instance, if remote 416 control of camera is offered, the APIs should be available to let 417 the local participant to figure out who's controlling the camera, 418 and possibly decide to revoke the permission for camera usage. 420 o Automatic gain control, if present, should normalize a speaking 421 voice into 424 o 426 The requirements on RTCWEB systems in this category are found in 427 . 429 10. IANA Considerations 431 This document makes no request of IANA. 433 Note to RFC Editor: this section may be removed on publication as an 434 RFC. 436 11. Security Considerations 438 Security of the web-enabled real time communications comes in several 439 pieces: 441 o Security of the components: The browsers, and other servers 442 involved. The most target-rich environment here is probably the 443 browser; the aim here should be that the introduction of these 444 components introduces no additional vulnerability. 446 o Security of the communication channels: It should be easy for a 447 participant to reassure himself of the security of his 448 communication - by verifying the crypto parameters of the links he 449 himself participates in, and to get reassurances from the other 450 parties to the communication that they promise that appropriate 451 measures are taken. 453 o Security of the partners' identity: verifying that the 454 participants are who they say they are (when positive 455 identification is appropriate), or that their identity cannot be 456 uncovered (when anonymity is a goal of the application). 458 The security analysis, and the requirements derived from that 459 analysis, is contained in . 461 12. Acknowledgements 463 The number of people who have taken part in the discussions 464 surroounding this draft are too numerous to list, or even to 465 identify. The ones below have made special, identifiable 466 contributions; this does not mean that others' contributions are less 467 important. 469 Thanks to Cary Bran, Cullen Jennings, Colin Perkins, Magnus 470 Westerlund and Joerg Ott, who offered techincal contributions on 471 various versions of the draft. 473 Thanks to Justin Uberti and Simon Leinen for document review. 475 13. References 477 13.1. Normative References 479 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 480 Requirement Levels", BCP 14, RFC 2119, March 1997. 482 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 483 Jacobson, "RTP: A Transport Protocol for Real-Time 484 Applications", STD 64, RFC 3550, July 2003. 486 13.2. Informative References 488 [RFC3935] Alvestrand, H., "A Mission Statement for the IETF", 489 BCP 95, RFC 3935, October 2004. 491 Appendix A. Change log 493 This section may be deleted by the RFC Editor when preparing for 494 publication. 496 A.1. Changes from draft-alvestrand-dispatch-rtcweb-datagram-00 to -01 498 Added section "On interoperability and innovation" 500 Added data confidentiality and integrity to the "data framing" layer 502 Added congestion management requirements in the "data transport" 503 layer section 505 Changed need for non-media data from "question: do we need this?" to 506 "Open issue: How do we do this?" 508 Strengthened disclaimer that listed codecs are placeholders, not 509 decisions. 511 More details on why the "local system support functions" section is 512 there. 514 A.2. Changes from draft-alvestrand-dispatch-01 to 515 draft-alvestrand-rtcweb-overview-00 517 Added section on "Relationship between API and protocol" 519 Added terminology section 521 Mentioned congestion management as part of the "data transport" layer 522 in the layer list 524 A.3. Changes from draft-alvestrand-rtcweb-00 to -01 526 Removed most technical content, and replaced with pointers to drafts 527 as requested and identified by the RTCWEB WG chairs. 529 Added content to acknowledgements section. 531 Added change log. 533 Spell-checked document. 535 A.4. Changes from draft-alvestrand-rtcweb-overview-01 to 536 draft-ietf-rtcweb-overview-00 538 Changed draft name and document date. 540 Removed unused references 542 Author's Address 544 Harald T. Alvestrand 545 Google 546 Kungsbron 2 547 Stockholm, 11122 548 Sweden 550 Email: harald@alvestrand.no