Network Working Group                                      H. Alvestrand
Internet-Draft                                                    Google
Intended status: Standards Track                       December 14, 2012
Expires: June 17, 2013

      Overview: Real Time Protocols for Brower-based Applications


   This document gives an overview and context of a protocol suite
   intended for use with real-time applications that can be deployed in
   browsers - "real time communication on the Web".

   It intends to serve as a starting and coordination point to make sure
   all the parts that are needed to achieve this goal are findable, and
   that the parts that belong in the Internet protocol suite are fully
   specified and on the right publication track.

   This document is a work item of the RTCWEB working group.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 17, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Principles and Terminology . . . . . . . . . . . . . . . . . .  5
     2.1.  Goals of this document . . . . . . . . . . . . . . . . . .  5
     2.2.  Relationship between API and protocol  . . . . . . . . . .  5
     2.3.  On interoperability and innovation . . . . . . . . . . . .  6
     2.4.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  7
   3.  Architecture and Functionality groups  . . . . . . . . . . . .  8
   4.  Data transport . . . . . . . . . . . . . . . . . . . . . . . . 12
   5.  Data framing and securing  . . . . . . . . . . . . . . . . . . 13
   6.  Data formats . . . . . . . . . . . . . . . . . . . . . . . . . 13
   7.  Connection management  . . . . . . . . . . . . . . . . . . . . 13
   8.  Presentation and control . . . . . . . . . . . . . . . . . . . 14
   9.  Local system support functions . . . . . . . . . . . . . . . . 14
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     13.2. Informative References . . . . . . . . . . . . . . . . . . 18
   Appendix A.  Transport and Middlebox specification . . . . . . . . 19
     A.1.  System-provided interfaces . . . . . . . . . . . . . . . . 19
     A.2.  Middle box related functions . . . . . . . . . . . . . . . 19
     A.3.  Transport protocols implemented  . . . . . . . . . . . . . 20
   Appendix B.  Change log  . . . . . . . . . . . . . . . . . . . . . 20
     B.1.  Changes from
           draft-alvestrand-dispatch-rtcweb-datagram-00 to -01  . . . 20
     B.2.  Changes from draft-alvestrand-dispatch-01 to
           draft-alvestrand-rtcweb-overview-00  . . . . . . . . . . . 20
     B.3.  Changes from draft-alvestrand-rtcweb-00 to -01 . . . . . . 20
     B.4.  Changes from draft-alvestrand-rtcweb-overview-01 to
           draft-ietf-rtcweb-overview-00  . . . . . . . . . . . . . . 21
     B.5.  Changes from -00 to -01 of draft-ietf-rtcweb-overview  . . 21
     B.6.  Changes from -01 to -02 of draft-ietf-rtcweb-overview  . . 21

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     B.7.  Changes from -02 to -03 of draft-ietf-rtcweb-overview  . . 21
     B.8.  Changes from -03 to -04 of draft-ietf-rtcweb-overview  . . 22
     B.9.  Changes from -04 to -05 of draft-ietf-rtcweb-overview  . . 22
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 22

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1.  Introduction

   The Internet was, from very early in its lifetime, considered a
   possible vehicle for the deployment of real-time, interactive
   applications - with the most easily imaginable being audio
   conversations (aka "Internet telephony") and video conferencing.

   The first attempts to build this were dependent on special networks,
   special hardware and custom-built software, often at very high prices
   or at low quality, placing great demands on the infrastructure.

   As the available bandwidth has increased, and as processors and other
   hardware has become ever faster, the barriers to participation have
   decreased, and it has become possible to deliver a satisfactory
   experience on commonly available computing hardware.

   Still, there are a number of barriers to the ability to communicate
   universally - one of these is that there is, as of yet, no single set
   of communication protocols that all agree should be made available
   for communication; another is the sheer lack of universal
   identification systems (such as is served by telephone numbers or
   email addresses in other communications systems).

   Development of The Universal Solution has proved hard, however, for
   all the usual reasons.

   The last few years have also seen a new platform rise for deployment
   of services: The browser-embedded application, or "Web application".
   It turns out that as long as the browser platform has the necessary
   interfaces, it is possible to deliver almost any kind of service on

   Traditionally, these interfaces have been delivered by plugins, which
   had to be downloaded and installed separately from the browser; in
   the development of HTML5, application developers see much promise in
   the possibility of making those interfaces available in a
   standardized way within the browser.

   This memo describes a set of building blocks that can be made
   accessible and controllable through a Javascript API in a browser,
   and which together form a sufficient set of functions to allow the
   use of interactive audio and video in applications that communicate
   directly between browsers across the Internet.  The resulting
   protocol suite is intended to enable all the applications that are
   described as required scenarios in the RTCWEB use cases document

   Other efforts, for instance the W3C WebRTC, Web Applications and

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   Device API working groups, focus on making standardized APIs and
   interfaces available, within or alongside the HTML5 effort, for those
   functions; this memo concentrates on specifying the protocols and
   subprotocols that are needed to specify the interactions that happen
   across the network.

2.  Principles and Terminology

2.1.  Goals of this document

   The goal of the RTCWEB protocol specification is to specify a set of
   protocols that, if all are implemented, will allow an implementation
   to communicate with another implementation using audio, video and
   data sent along the most direct possible path between the

   This document is intended to serve as the roadmap to the RTCWEB
   specifications.  It defines terms used by other pieces of
   specification, lists references to other specifications that don't
   need further elaboration in the RTCWEB context, and gives pointers to
   other documents that form part of the RTCWEB suite.

   By reading this document and the documents it refers to, it should be
   possible to have all information needed to implement an RTCWEB
   compatible implementation.

2.2.  Relationship between API and protocol

   The total RTCWEB/WEBRTC effort consists of two pieces:

   o  A protocol specification, done in the IETF

   o  A Javascript API specification, done in the W3C

   Together, these two specifications aim to provide an environment
   where Javascript embedded in any page, viewed in any compatible
   browser, when suitably authorized by its user, is able to set up
   communication using audio, video and auxiliary data, where the
   browser environment does not constrain the types of application in
   which this functionality can be used.

   The protocol specification does not assume that all implementations
   implement this API; it is not intended to be necessary for
   interoperation to know whether the entity one is communicating with
   is a browser or another device implementing this specification.

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   The goal of cooperation between the protocol specification and the
   API specification is that for all options and features of the
   protocol specification, it should be clear which API calls to make to
   exercise that option or feature; similarly, for any sequence of API
   calls, it should be clear which protocol options and features will be
   invoked.  Both subject to constraints of the implementation, of

2.3.  On interoperability and innovation

   The "Mission statement of the IETF" [RFC3935] states that "The
   benefit of a standard to the Internet is in interoperability - that
   multiple products implementing a standard are able to work together
   in order to deliver valuable functions to the Internet's users."

   Communication on the Internet frequently occurs in two phases:

   o  Two parties communicate, through some mechanism, what
      functionality they both are able to support

   o  They use that shared communicative functionality to communicate,
      or, failing to find anything in common, give up on communication.

   There are often many choices that can be made for communicative
   functionality; the history of the Internet is rife with the proposal,
   standardization, implementation, and success or failure of many types
   of options, in all sorts of protocols.

   The goal of having a mandatory to implement function set is to
   prevent negotiation failure, not to preempt or prevent negotiation.

   The presence of a mandatory to implement function set serves as a
   strong changer of the marketplace of deployment - in that it gives a
   guarantee that, as long as you conform to a specification, and the
   other party is willing to accept communication at the base level of
   that specification, you can communicate successfully.

   The alternative - that of having no mandatory to implement - does not
   mean that you cannot communicate, it merely means that in order to be
   part of the communications partnership, you have to implement the
   standard "and then some" - that "and then some" usually being called
   a profile of some sort; in the version most antithetical to the
   Internet ethos, that "and then some" consists of having to use a
   specific vendor's product only.

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2.4.  Terminology

   The following terms are used in this document, and as far as possible
   across the documents specifying the RTCWEB suite, in the specific
   meanings given here.  Not all terms are used in this document.  Other
   terms are used in their commonly used meaning.

   The list is in alphabetical order.

   Agent:  Undefined term.  See "SDP Agent" and "ICE Agent".

   API:  Application Programming Interface - a specification of a set of
      calls and events, usually tied to a programming language or an
      abstract formal specification such as WebIDL, with its defined

   Browser:  Used synonymously with "Interactive User Agent" as defined
      in the HTML specification [W3C.WD-html5-20110525].

   ICE Agent:  An implementation of the ICE [RFC5245] protocol.  An ICE
      Agent may also be an SDP Agent, but there exist ICE Agents that do
      not use SDP (for instance those that use Jingle).

   Interactive:  Communication between multiple parties, where the
      expectation is that an action from one party can cause a reaction
      by another party, and the reaction can be observed by the first
      party, with the total time required for the action/reaction/
      observation is on the order of no more than hundreds of

   Media:  Audio and video content.  Not to be confused with
      "transmission media" such as wires.

   Media path:  The path that media data follows from one browser to

   Protocol:  A specification of a set of data units, their
      representation, and rules for their transmission, with their
      defined semantics.  A protocol is usually thought of as going
      between systems.

   Real-time media:  Media where generation of content and display of
      content are intended to occur closely together in time (on the
      order of no more than hundreds of milliseconds).  Real-time media
      can be used to support interactive communication.

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   SDP Agent:  The protocol implementation involved in the SDP offer/
      answer exchange, as defined in [RFC3264] section 3.

   Signaling:  Communication that happens in order to establish, manage
      and control media paths.

   Signaling Path:  The communication channels used between entities
      participating in signaling to transfer signaling.  There may be
      more entities in the signaling path than in the media path.

   NOTE: Where common definitions exist for these terms, those
   definitions should be used to the greatest extent possible.

   TODO: Extend this list with other terms that might prove slippery.

3.  Architecture and Functionality groups

   The model of real-time support for browser-based applications does
   not envisage that the browser will contain all the functions that
   need to be performed in order to have a function such as a telephone
   or a video conferencing unit; the vision is that the browser will
   have the functions that are needed for a Web application, working in
   conjunction with its backend servers, to implement these functions.

   This means that two vital interfaces need specification: The
   protocols that browsers talk to each other, without any intervening
   servers, and the APIs that are offered for a Javascript application
   to take advantage of the browser's functionality.

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                        +------------------------+  On-the-wire
                        |                        |  Protocols
                        |      Servers           |--------->
                        |                        |
                        |                        |
                                    | HTTP/
                                    | Websockets
                      |    Javascript/HTML/CSS     |
                   Other  ^                 ^RTC
                   APIs   |                 |APIs
                      |   |                 |      |
                      |                 +---------+|
                      |                 | Browser ||  On-the-wire
                      | Browser         | RTC     ||  Protocols
                      |                 | Function|----------->
                      |                 |         ||
                      |                 |         ||
                      |                 +---------+|
                                       Native OS Services

                          Figure 1: Browser Model

   Note that HTTP and Websockets are also offered to the Javascript
   application through browser APIs.

   As for all protocol and API specifications, there is no restriction
   that the protocols can only be used to talk to another browser; since
   they are fully specified, any device that implements the protocols
   faithfully should be able to interoperate with the application

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   running in the browser.

   A commonly imagined model of deployment is the one depicted below.

                +-----------+             +-----------+
                |   Web     |             |   Web     |
                |           |  Signaling  |           |
                |           |-------------|           |
                |  Server   |   path      |  Server   |
                |           |             |           |
                +-----------+             +-----------+
                     /                           \
                    /                             \ Application-defined
                   /                               \ over
                  /                                 \ HTTP/Websockets
                 /  Application-defined over         \
                /   HTTP/Websockets                   \
               /                                       \
         +-----------+                           +-----------+
         |JS/HTML/CSS|                           |JS/HTML/CSS|
         +-----------+                           +-----------+
         +-----------+                           +-----------+
         |           |                           |           |
         |           |                           |           |
         |  Browser  | ------------------------- |  Browser  |
         |           |          Media path       |           |
         |           |                           |           |
         +-----------+                           +-----------+

                      Figure 2: Browser RTC Trapezoid

   On this drawing, the critical part to note is that the media path
   ("low path") goes directly between the browsers, so it has to be
   conformant to the specifications of the RTCWEB protocol suite; the
   signaling path ("high path") goes via servers that can modify,
   translate or massage the signals as needed.

   If the two Web servers are operated by different entities, the inter-
   server signaling mechanism needs to be agreed upon, either by
   standardization or by other means of agreement.  Existing protocols
   (for example SIP or XMPP) could be used between servers, while either
   a standards-based or proprietary protocol could be used between the
   browser and the web server.

   For example, if both operators' servers implement SIP, SIP could be
   used for communication between servers, along with either a
   standardized signaling mechanism (e.g.  SIP over Websockets) or a

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   proprietary signaling mechanism used between the application running
   in the browser and the web server.  Similarly, if both operators'
   servers implement XMPP, XMPP could be used for communication between
   XMPP servers, with either a standardized signaling mechanism (e.g.
   XMPP over Websockets or BOSH) or a proprietary signaling mechanism
   used between the application running in the browser and the web

   The choice of protocols, and definition of the translation between
   them, is outside the scope of the RTCWEB standards suite described in
   the document.

   The functionality groups that are needed in the browser can be
   specified, more or less from the bottom up, as:

   o  Data transport: TCP, UDP and the means to securely set up
      connections between entities, as well as the functions for
      deciding when to send data: Congestion management, bandwidth
      estimation and so on.

   o  Data framing: RTP and other data formats that serve as containers,
      and their functions for data confidentiality and integrity.

   o  Data formats: Codec specifications, format specifications and
      functionality specifications for the data passed between systems.
      Audio and video codecs, as well as formats for data and document
      sharing, belong in this category.  In order to make use of data
      formats, a way to describe them, a session description, is needed.

   o  Connection management: Setting up connections, agreeing on data
      formats, changing data formats during the duration of a call; SIP
      and Jingle/XMPP belong in this category.

   o  Presentation and control: What needs to happen in order to ensure
      that interactions behave in a non-surprising manner.  This can
      include floor control, screen layout, voice activated image
      switching and other such functions - where part of the system
      require the cooperation between parties.  XCON and Cisco/
      Tandberg's TIP were some attempts at specifying this kind of
      functionality; many applications have been built without
      standardized interfaces to these functions.

   o  Local system support functions: These are things that need not be
      specified uniformly, because each participant may choose to do
      these in a way of the participant's choosing, without affecting
      the bits on the wire in a way that others have to be cognizant of.
      Examples in this category include echo cancellation (some forms of
      it), local authentication and authorization mechanisms, OS access

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      control and the ability to do local recording of conversations.

   Within each functionality group, it is important to preserve both
   freedom to innovate and the ability for global communication.
   Freedom to innovate is helped by doing the specification in terms of
   interfaces, not implementation; any implementation able to
   communicate according to the interfaces is a valid implementation.
   Ability to communicate globally is helped both by having core
   specifications be unencumbered by IPR issues and by having the
   formats and protocols be fully enough specified to allow for
   independent implementation.

   One can think of the three first groups as forming a "media transport
   infrastructure", and of the three last groups as forming a "media
   service".  In many contexts, it makes sense to use a common
   specification for the media transport infrastructure, which can be
   embedded in browsers and accessed using standard interfaces, and "let
   a thousand flowers bloom" in the "media service" layer; to achieve
   interoperable services, however, at least the first five of the six
   groups need to be specified.

4.  Data transport

   Data transport refers to the sending and receiving of data over the
   network interfaces, the choice of network-layer addresses at each end
   of the communication, and the interaction with any intermediate
   entities that handle the data, but do not modify it (such as TURN

   It includes necessary functions for congestion control: When not to
   send data.

   T are described in <WORKING GROUP DRAFT "TRANSPORTS">.

   ICE is required for all media paths that use UDP; in addition to the
   ability to pass NAT boxes, ICE fulfills the need for guaranteeing
   that the media path is going to a UDP port that is willing to receive
   the data.

   The data transport protocols used by RTCWEB, as well as the details
   of interactions with intermediate boxes, such as firewalls, relays
   and NAT boxes, are intended to be described in a separate document;
   for now, notes are gathered in Appendix A.

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5.  Data framing and securing

   The format for media transport is RTP [RFC3550].  Implementation of
   SRTP [RFC3711] is required for all implementations.

   The detailed considerations for usage of functions from RTP and SRTP
   are given in [I-D.ietf-rtcweb-rtp-usage].  The security
   considerations for the RTCWEB use case are in
   [I-D.ietf-rtcweb-security], and the resulting security functions are
   described in [I-D.ietf-rtcweb-security-arch].

   Considerations for the transfer of data that is not in RTP format is
   described in [I-D.ietf-rtcweb-data-channel], and the resulting
   protocol is described in [I-D.jesup-rtcweb-data-protocol] (not yet a
   WG document)

6.  Data formats

   The intent of this specification is to allow each communications
   event to use the data formats that are best suited for that
   particular instance, where a format is supported by both sides of the
   connection.  However, a minimum standard is greatly helpful in order
   to ensure that communication can be achieved.  This document
   specifies a minimum baseline that will be supported by all
   implementations of this specification, and leaves further codecs to
   be included at the will of the implementor.

   The mandatory to implement codecs, as well as any profiling
   requirements for both mandatory and optional codecs, is described in

7.  Connection management

   The methods, mechanisms and requirements for setting up, negotiating
   and tearing down connections is a large subject, and one where it is
   desirable to have both interoperability and freedom to innovate.

   The following principles apply:

   1.  The RTCWEB media negotiations will be capable of representing the
       same SDP offer/answer semantics that are used in SIP [RFC3264],
       in such a way that it is possible to build a signaling gateway
       between SIP and the RTCWEB media negotiation.

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   2.  It will be possible to gateway between legacy SIP devices that
       support ICE and appropriate RTP / SDP mechanisms, codecs and
       security mechanisms without using a media gateway.  A signaling
       gateway to convert between the signaling on the web side to the
       SIP signaling may be needed.

   3.  When a new codec is specified, and the SDP for the new codec is
       specified in the MMUSIC WG, no other standardization should be
       required for it to be possible to use that in the web browsers.
       Adding new codecs which might have new SDP parameters should not
       change the APIs between the browser and Javascript application.
       As soon as the browsers support the new codecs, old applications
       written before the codecs were specified should automatically be
       able to use the new codecs where appropriate with no changes to
       the JS applications.

   The particular choices made for RTCWEB, and their implications for
   the API offered by a browser implementing RTCWEB, are described in

8.  Presentation and control

   The most important part of control is the user's control over the
   browser's interaction with input/output devices and communications
   channels.  It is important that the user have some way of figuring
   out where his audio, video or texting is being sent, for what
   purported reason, and what guarantees are made by the parties that
   form part of this control channel.  This is largely a local function
   between the browser, the underlying operating system and the user
   interface; this is being worked on as part of the W3C API effort, and
   will be part of the peer connection API [W3C.WD-webrtc-20120209], and
   the device control API [getusermedia].  Considerations for the
   implications of wanting to identify correspondents are described in
   [I-D.rescorla-rtcweb-generic-idp] (not a WG item).

9.  Local system support functions

   These are characterized by the fact that the quality of these
   functions strongly influence the user experience, but the exact
   algorithm does not need coordination.  In some cases (for instance
   echo cancellation, as described below), the overall system definition
   may need to specify that the overall system needs to have some
   characteristics for which these facilities are useful, without
   requiring them to be implemented a certain way.

   Local functions include echo cancellation, volume control, camera

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   management including focus, zoom, pan/tilt controls (if available),
   and more.

   Certain parts of the system SHOULD conform to certain properties, for

   o  Echo cancellation should be good enough to achieve the suppression
      of acoustical feedback loops below a perceptually noticeable

   o  Privacy concerns must be satisfied; for instance, if remote
      control of camera is offered, the APIs should be available to let
      the local participant figure out who's controlling the camera, and
      possibly decide to revoke the permission for camera usage.

   o  Automatic gain control, if present, should normalize a speaking
      voice into <whatever dB metrics makes sense here - most important
      that we have one only>

   The requirements on RTCWEB systems in this category are found in
   control of local devices are found in [getusermedia].

10.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an

11.  Security Considerations

   Security of the web-enabled real time communications comes in several

   o  Security of the components: The browsers, and other servers
      involved.  The most target-rich environment here is probably the
      browser; the aim here should be that the introduction of these
      components introduces no additional vulnerability.

   o  Security of the communication channels: It should be easy for a
      participant to reassure himself of the security of his
      communication - by verifying the crypto parameters of the links he
      himself participates in, and to get reassurances from the other
      parties to the communication that they promise that appropriate
      measures are taken.

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   o  Security of the partners' identity: verifying that the
      participants are who they say they are (when positive
      identification is appropriate), or that their identity cannot be
      uncovered (when anonymity is a goal of the application).

   The security analysis, and the requirements derived from that
   analysis, is contained in [I-D.ietf-rtcweb-security].

12.  Acknowledgements

   The number of people who have taken part in the discussions
   surrounding this draft are too numerous to list, or even to identify.
   The ones below have made special, identifiable contributions; this
   does not mean that others' contributions are less important.

   Thanks to Cary Bran, Cullen Jennings, Colin Perkins, Magnus
   Westerlund and Joerg Ott, who offered technical contributions on
   various versions of the draft.

   Thanks to Jonathan Rosenberg, Matthew Kaufman and others at Skype for
   the ASCII drawings in section 1.

   Thanks to Eric Rescorla, Justin Uberti, Henry Sinnreich, Colin
   Perkins and Simon Leinen for document review, ad to Heath Matlock for
   grammatical review.

13.  References

13.1.  Normative References

              Loreto, S. and G. Camarillo, "Stream Control Transmission
              Protocol (SCTP)-Based Media Transport in the Session
              Description Protocol (SDP)", draft-ietf-mmusic-sctp-sdp-01
              (work in progress), March 2012.

              Jesup, R., Loreto, S., and M. Tuexen, "RTCWeb Datagram
              Connection", draft-ietf-rtcweb-data-channel-00 (work in
              progress), March 2012.

              Uberti, J. and C. Jennings, "Javascript Session
              Establishment Protocol", draft-ietf-rtcweb-jsep-01 (work
              in progress), June 2012.

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              Perkins, C., Westerlund, M., and J. Ott, "Web Real-Time
              Communication (WebRTC): Media Transport and Use of RTP",
              draft-ietf-rtcweb-rtp-usage-04 (work in progress),
              July 2012.

              Rescorla, E., "Security Considerations for RTC-Web",
              draft-ietf-rtcweb-security-03 (work in progress),
              June 2012.

              Rescorla, E., "RTCWEB Security Architecture",
              draft-ietf-rtcweb-security-arch-03 (work in progress),
              July 2012.

              Nandakumar, S., Salgueiro, G., Jones, P., and M. Petit-
              Huguenin, "URI Scheme for Session Traversal Utilities for
              NAT (STUN) Protocol", draft-nandakumar-rtcweb-stun-uri-01
              (work in progress), March 2012.

              Jesup, R., Loreto, S., Stewart, R., and M. Tuexen, "DTLS
              Encapsulation of SCTP Packets for RTCWEB",
              draft-tuexen-tsvwg-sctp-dtls-encaps-01 (work in progress),
              July 2012.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              June 2002.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, March 2004.

   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245,
              April 2010.

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   [RFC5766]  Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
              Relays around NAT (TURN): Relay Extensions to Session
              Traversal Utilities for NAT (STUN)", RFC 5766, April 2010.

13.2.  Informative References

              Bran, C., Jennings, C., and J. Valin, "WebRTC Codec and
              Media Processing Requirements",
              draft-cbran-rtcweb-codec-02 (work in progress),
              March 2012.

              Holmberg, C., Hakansson, S., and G. Eriksson, "Web Real-
              Time Communication Use-cases and Requirements",
              draft-ietf-rtcweb-use-cases-and-requirements-09 (work in
              progress), June 2012.

              Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel
              Protocol", draft-jesup-rtcweb-data-protocol-02 (work in
              progress), July 2012.

              Rescorla, E., "RTCWEB Generic Identity Provider
              Interface", draft-rescorla-rtcweb-generic-idp-01 (work in
              progress), March 2012.

   [RFC3935]  Alvestrand, H., "A Mission Statement for the IETF",
              BCP 95, RFC 3935, October 2004.

              Hickson, I., "HTML5", World Wide Web Consortium
              LastCall WD-html5-20110525, May 2011,

              Bergkvist, A., Burnett, D., Narayanan, A., and C.
              Jennings, "WebRTC 1.0: Real-time Communication Between
              Browsers", World Wide Web Consortium WD WD-webrtc-
              20120209, February 2012,

              Burnett, D. and A. Narayanan, "getusermedia: Getting
              access to local devices that can generate multimedia
              streams", December 2011,

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Appendix A.  Transport and Middlebox specification

   The draft referred to as "transport and middle boxes" in Section 4
   has not been written yet.  This appendix contains some keywords to
   what it should say; this also serves the purpose of linking to the
   drafts-in-progress that are relevant to this specification.

A.1.  System-provided interfaces

   The protocol specifications used here assume that the following
   protocols are available as system-level interfaces:

   o  UDP.  This is the protocol assumed by most protocol elements

   o  TCP.  This is used for HTTP/WebSockets, as well as for TURN/SSL
      and ICE-TCP.

   For both protocols, we assume the ability to set the DSCP code point
   of the sockets opened.  We do not assume that the DSCP codepoints
   will be honored, and we do assume that they may be zeroed or changed,
   since this is a local configuration issue.

   We do not assume that the implementation will have access to ICMP or
   raw IP.

A.2.  Middle box related functions

   The primary mechanism to deal with middle boxes is ICE, which is an
   appropriate way to deal with NAT boxes and firewalls that accept
   traffic from the inside, but only from the outside if it's in
   response to inside traffic (simple stateful firewalls).

   In order to deal with symmetric NATs, TURN MUST be supported.

   In order to deal with firewalls that block all UDP traffic, TURN over
   TCP MUST be supported.  (QUESTION: What about ICE-TCP?)

   The following specifications MUST be supported:

   o  ICE [RFC5245]

   o  TURN, including TURN over TCP [[QUESTION: and TURN over TLS]],

   For referring to ICE servers, we use the STUN URI,

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A.3.  Transport protocols implemented

   For data transport, we implement SCTP over DTLS over ICE.  This is
   specified in [I-D.tuexen-tsvwg-sctp-dtls-encaps].  Negotiation of
   this transport in SCTP is defined in [I-D.ietf-mmusic-sctp-sdp].

Appendix B.  Change log

   This section may be deleted by the RFC Editor when preparing for

B.1.  Changes from draft-alvestrand-dispatch-rtcweb-datagram-00 to -01

   Added section "On interoperability and innovation"

   Added data confidentiality and integrity to the "data framing" layer

   Added congestion management requirements in the "data transport"
   layer section

   Changed need for non-media data from "question: do we need this?" to
   "Open issue: How do we do this?"

   Strengthened disclaimer that listed codecs are placeholders, not

   More details on why the "local system support functions" section is

B.2.  Changes from draft-alvestrand-dispatch-01 to

   Added section on "Relationship between API and protocol"

   Added terminology section

   Mentioned congestion management as part of the "data transport" layer
   in the layer list

B.3.  Changes from draft-alvestrand-rtcweb-00 to -01

   Removed most technical content, and replaced with pointers to drafts
   as requested and identified by the RTCWEB WG chairs.

   Added content to acknowledgments section.

   Added change log.

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   Spell-checked document.

B.4.  Changes from draft-alvestrand-rtcweb-overview-01 to

   Changed draft name and document date.

   Removed unused references

B.5.  Changes from -00 to -01 of draft-ietf-rtcweb-overview

   Added architecture figures to section 2.

   Changed the description of "echo cancellation" under "local system
   support functions".

   Added a few more definitions.

B.6.  Changes from -01 to -02 of draft-ietf-rtcweb-overview

   Added pointers to use cases, security and rtp-usage drafts (now WG

   Changed description of SRTP from mandatory-to-use to mandatory-to-

   Added the "3 principles of negotiation" to the connection management

   Added an explicit statement that ICE is required for both NAT and

B.7.  Changes from -02 to -03 of draft-ietf-rtcweb-overview

   Added references to a number of new drafts.

   Expanded the description text under the "trapezoid" drawing with some
   more text discussed on the list.

   Changed the "Connection management" sentence from "will be done using
   SDP offer/answer" to "will be capable of representing SDP offer/
   answer" - this seems more consistent with JSEP.

   Added "security mechanisms" to the things a non-gatewayed SIP devices
   must support in order to not need a media gateway.

   Added a definition for "browser".

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B.8.  Changes from -03 to -04 of draft-ietf-rtcweb-overview

   Made introduction more normative.

   Several wording changes in response to review comments from EKR

   Added Appendix A to hold references and notes that are not yet in a
   separate document.

B.9.  Changes from -04 to -05 of draft-ietf-rtcweb-overview

   Minor grammatical fixes.  This is mainly a "keepalive" refresh.

Author's Address

   Harald T. Alvestrand
   Kungsbron 2
   Stockholm,   11122


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