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<!DOCTYPE html>
<!--
To publish this document, see instructions in README
-->
<html lang="en">
<head>
<meta charset="utf-8">
<link href="webrtc.css" rel="stylesheet">
<title>WebRTC 1.0: Real-time Communication Between Browsers</title>
<script class="remove" src="http://www.w3.org/Tools/respec/respec-w3c-common"
type="text/javascript">
// // keep this comment //
</script>
<script class="remove" src="webrtc.js" type="text/javascript">
// // keep
this comment //
</script>
</head>
<body>
<section id="abstract">
<p>This document defines a set of ECMAScript APIs in WebIDL to allow media
to be sent to and received from another browser or device implementing the
appropriate set of real-time protocols. This specification is being
developed in conjunction with a protocol specification developed by the
IETF RTCWEB group and an API specification to get access to local media
devices developed by the Media Capture Task Force.</p>
</section>
<section id="sotd">
<p>The Editors and active contributors of WebRTC 1.0 intend to publish a
Candidate Recommendation soon. Consequently, this is a Request for Comments
by the WebRTC Working Group to seek wide review of this document.</p>
<p>The API is based on preliminary work done in the WHATWG.</p>
</section>
<section class="informative" id="intro">
<h2>Introduction</h2>
<p>There are a number of facets to video-conferencing in HTML covered by
this specification:</p>
<ul>
<li>Connecting to remote peers using NAT-traversal technologies such as
ICE, STUN, and TURN.</li>
<li>Sending the locally-produced tracks to remote peers and receiving
tracks from remote peers.</li>
<li>Sending arbitrary data directly to remote peers.</li>
</ul>
<p>This document defines the APIs used for these features. This
specification is being developed in conjunction with a protocol
specification developed by the <a href=
"https://datatracker.ietf.org/wg/rtcweb/">IETF RTCWEB group</a> and an API
specification to get access to local media devices
[[!GETUSERMEDIA]] developed by the <a href=
"https://www.w3.org/wiki/Media_Capture">Media Capture Task Force</a>. An
overview of the system can be found in [[RTCWEB-OVERVIEW]] and
[[RTCWEB-SECURITY]].</p>
</section>
<section id="conformance">
<p>This specification defines conformance criteria that apply to a single
product: the <dfn>user agent</dfn> that implements the interfaces that it
contains with the exception of the <code><a>RTCIdentityProvider</a></code>
interface which is used by the
user agent but not implemented by the user agent.</p>
<p>It also defines conformance criteria for identity providers which provide
implementations of the <code><a>RTCIdentityProvider</a></code>
interface.</p>
<p>Conformance requirements phrased as algorithms or specific steps may be
implemented in any manner, so long as the end result is equivalent. (In
particular, the algorithms defined in this specification are intended to be
easy to follow, and not intended to be performant.)</p>
<p>Implementations that use ECMAScript to implement the APIs defined in
this specification MUST implement them in a manner consistent with the
ECMAScript Bindings defined in the Web IDL specification [[!WEBIDL-1]], as
this specification uses that specification and terminology.</p>
</section>
<section>
<h2>Terminology</h2>
<p>The <code><a href=
"http://dev.w3.org/html5/spec/webappapis.html#eventhandler">EventHandler</a></code>
interface, representing a callback used for event handlers, and the
<a href="http://dev.w3.org/html5/spec/webappapis.html#errorevent"><code><dfn>ErrorEvent</dfn></code></a>
interface are defined in [[!HTML5]].</p>
<p>The concepts <dfn><a href=
"http://dev.w3.org/html5/spec/webappapis.html#queue-a-task">queue a
task</a></dfn>, <dfn><a href=
"http://dev.w3.org/html5/spec/webappapis.html#fire-a-simple-event">fire a
simple event</a></dfn> and <dfn><a href=
"http://dev.w3.org/html5/spec/webappapis.html#networking-task-source">networking task source</a></dfn> are defined in [[!HTML5]].</p>
<p>The terms <dfn>event</dfn>, <dfn><a href=
"http://dev.w3.org/html5/spec/webappapis.html#event-handlers">event
handlers</a></dfn> and <dfn><a href=
"http://dev.w3.org/html5/spec/webappapis.html#event-handler-event-type">event
handler event types</a></dfn> are defined in [[!HTML5]].</p>
<p>The terms <dfn>MediaStream</dfn>, <dfn>MediaStreamTrack</dfn>, and
<dfn>MediaStreamConstraints</dfn> are defined in [[!GETUSERMEDIA]].</p>
<p>The term <dfn>media description</dfn> is defined in [[!RFC4566]].</p>
</section>
<section>
<h2>Peer-to-peer connections</h2>
<section>
<h3>Introduction</h3>
<p>An <code><a>RTCPeerConnection</a></code> instance allows to establish
peer to peer communications. Communications are coordinated
via a signaling channel which is provided by unspecified means, but
generally by a script in the page via the server, e.g. using
<code>XMLHttpRequest</code> [[XMLHttpRequest]] or Web Sockets
[[WEBSOCKETS-API]].</p>
</section>
<section>
<h3>Configuration</h3>
<section>
<h4>RTCConfiguration Dictionary</h4>
<p>The <code>RTCConfiguration</code> defines a set of parameters to
configure how the peer to peer communication established via
<code><a>RTCPeerConnection</a></code> is established or
re-established.</p>
<dl class="idl" title="dictionary RTCConfiguration">
<dt>sequence<RTCIceServer> iceServers</dt>
<dd>
<p>An array of objects describing servers available to be used by ICE,
such as STUN and TURN server.</p>
</dd>
<dt>RTCIceTransportPolicy iceTransportPolicy = "all"</dt>
<dd>
<p>Indicates which candidates the <a>ICE agent</a> is allowed to use.</p>
</dd>
<dt>RTCBundlePolicy bundlePolicy = "balanced"</dt>
<dd>
<p>Indicates which <a href="#target-bundle-policy">media-bundling policy</a> to use when gathering ICE candidates. </p>
</dd>
<dt>RTCRtcpMuxPolicy rtcpMuxPolicy = "require"</dt>
<dd>
<p>Indicates which <a href="#target-rtcp-mux-policy">rtcp-mux policy</a> to use when gathering ICE candidates. </p>
</dd>
<dt>DOMString peerIdentity</dt>
<dd>
<p>Sets the <a href="#target-peer-identity">target peer
identity</a> for the <a>RTCPeerConnection</a>. The
<a>RTCPeerConnection</a> will not establish a connection to a remote
peer unless it can be successfully authenticated with the provided
name.</p>
</dd>
<dt>sequence<RTCCertificate> certificates</dt>
<dd>
<p>A set of certificates that
the <a><code>RTCPeerConnection</code></a> uses to authenticate.</p>
<p>Valid values for this parameter are created through calls to
the <a href="#widl-RTCPeerConnection-generateCertificate-Promise-RTCCertificate--AlgorithmIdentifier-keygenAlgorithm"><code>generateCertificate</code></a>
function.</p>
<p>Although any given DTLS connection will use only one certificate,
this attribute allows the caller to provide multiple certificates
that support different algorithms. The final certificate will be
selected based on the DTLS handshake, which establishes which
certificates are allowed. The <code>RTCPeerConnection</code>
implementation selects which of the certificates is used for a given
connection; how certificates are selected is outside the scope of
this specification.</p>
<p>If this value is absent, then a set of certificates are generated
for each <a><code>RTCPeerConnection</code></a> instance.</p>
<p>This option allows applications to establish key continuity.
An <code>RTCCertificate</code> can be persisted in [[INDEXEDDB]] and
reused. Persistence and reuse also avoids the cost of key
generation.</p>
<p>The value for this configuration option cannot change after its
value is initially selected.</p>
</dd>
<dt>unsigned short iceCandidatePoolSize = 0</dt>
<dd>
<p>Size of the prefetched ICE pool as defined in <span data-jsep="ice-candidate-pool constructor">[[!JSEP]]</span></p>
</dd>
</dl>
</section>
<section>
<h4>RTCIceCredentialType Enum</h4>
<dl class="idl" title="enum RTCIceCredentialType">
<dt>password</dt>
<dd>The credential is a long-term authentication password, as
described in [[!RFC5389]], Section 10.2.
</dd>
<dt>token</dt>
<dd>The credential is an access token, as described in
[[!TRAM-TURN-THIRD-PARTY-AUTHZ]], Section 6.2.</dd>
</dl>
</section>
<section>
<h4>RTCIceServer Dictionary</h4>
<p>The <code>RTCIceServer</code> dictionary is used to describe the
STUN and TURN servers that can be used by the <a>ICE agent</a> to
establish a connection with a peer.</p>
<dl class="idl" title="dictionary RTCIceServer">
<dt>required (DOMString or sequence<DOMString>) urls</dt>
<dd>
<p>STUN or TURN URI(s) as defined in [[!RFC7064]] and [[!RFC7065]]
or other URI types.</p>
</dd>
<dt>DOMString username</dt>
<dd>
<p>If this <code><a>RTCIceServer</a></code> object represents a
TURN server, then this attribute specifies the username to use with
that TURN server.</p>
</dd>
<dt>DOMString credential</dt>
<dd>
<p>If this <code><a>RTCIceServer</a></code> object represents a
TURN server, then this attribute specifies the credential to use
with that TURN server.</p>
</dd>
<dt>RTCIceCredentialType credentialType = "password"</dt>
<dd>
<p>If this <code><a>RTCIceServer</a></code> object represents a
TURN server, then this attribute specifies how <var>credential</var>
should be used when that TURN server requests authorization.</p>
</dd>
</dl>
<p>An example array of RTCIceServer objects is:</p>
<pre class="example highlight"><code>[
{ "urls": "stun:stun1.example.net" },
{ "urls": ["turns:turn.example.org", "turn:turn.example.net"],
"username": "user",
"credential": "myPassword",
"credentialType": "password" }
]</code></pre>
</section>
<section>
<h4>RTCIceTransportPolicy Enum</h4>
<p>As noted in <span data-jsep="constructor">[[!JSEP]]</span>, if RTCIceTransportPolicy is specified,
it causes the browser to only surface the permitted
candidates to the application, and only use those candidates for
connectivity checks.</p>
<dl class="idl" title="enum RTCIceTransportPolicy">
<dt>public</dt>
<dd>The <a>ICE agent</a> MUST filter out candidates with private
IP addresses [[RFC1918]].</dd>
<dt>relay</dt>
<dd>The <a>ICE agent</a> MUST only use media relay candidates such as
candidates passing through a TURN server. This can be used to reduce
leakage of IP addresses in certain use cases.</dd>
<dt>all</dt>
<dd>The <a>ICE agent</a> may use any type of candidates when this value is
specified.</dd>
</dl>
</section>
<section>
<h4>RTCBundlePolicy Enum</h4>
<p>As described in <span data-jsep="constructor">[[!JSEP]]</span>, BUNDLE policy
affects which media tracks are negotiated if
the remote endpoint is not BUNDLE-aware, and what ICE
candidates are gathered. If the remote endpoint is
BUNDLE-aware, all media tracks and data channels are BUNDLEd
onto the same transport.</p>
<dl class="idl" title="enum RTCBundlePolicy" id="target-bundle-policy">
<dt>balanced</dt>
<dd>Gather ICE candidates for each media type in use (audio,
video, and data). If the remote endpoint is not
BUNDLE-aware, negotiate only one audio and video track on
separate transports.</dd>
<dt>max-compat</dt>
<dd>Gather ICE candidates for each track. If the remote
endpoint is not BUNDLE-aware, negotiate all media tracks on
separate transports.</dd>
<dt>max-bundle</dt>
<dd>Gather ICE candidates for only one track. If the remote
endpoint is not BUNDLE-aware, negotiate only one media
track.</dd>
</dl>
</section>
<section>
<h4>RTCRtcpMuxPolicy Enum</h4>
<p>Defined in <span data-jsep="constructor">[[!JSEP]]</span>. The following is a
non-normative summary for convenience.</p>
<p>The RtcpMuxPolicy affects what ICE candidates are gathered
to support non-multiplexed RTCP.</p>
<dl class="idl" title="enum RTCRtcpMuxPolicy" id="target-rtcp-mux-policy">
<dt>negotiate</dt>
<dd>Gather ICE candidates for both RTP and RTCP candidates.
If the remote-endpoint is capable of multiplexing RTCP,
multiplex RTCP on the RTP candidates. If it is not, use
both the RTP and RTCP candidates separately.</dd>
<dt>require</dt>
<dd>Gather ICE candidates only for RTP and multiplex RTCP on
the RTP candidates. If the remote endpoint is not capable
of rtcp-mux, session negotiation will fail.</dd>
</dl>
</section>
<section>
<h4>Offer/Answer Options</h4>
<p>These dictionaries describe the options that can be used to control
the offer/answer creation process.</p>
<dl class="idl" title="dictionary RTCOfferAnswerOptions">
<dt>boolean voiceActivityDetection = true</dt>
<dd>
<p>Many codecs and systems are capable of detecting "silence" and
changing their behavior in this case by doing things such as not
transmitting any media. In many cases, such as when dealing with
emergency calling or sounds other than spoken voice, it is
desirable to be able to turn off this behavior. This option allows
the application to provide information about whether it wishes this
type of processing enabled or disabled.</p>
</dd>
</dl>
<dl class="idl" title="dictionary RTCOfferOptions : RTCOfferAnswerOptions">
<dt>boolean iceRestart = false</dt>
<dd>
<p>When the value of this dictionary member is true, the generated
description will have ICE credentials that are different from the
current credentials (as visible in the
<code><a>localDescription</a></code> attribute's SDP). Applying the
generated description will restart ICE.</p>
<p>When the value of this dictionary member is false, and the
<code><a>localDescription</a></code> attribute has valid ICE
credentials, the generated description will have the same ICE
credentials as the current value from the
<code><a>localDescription</a></code> attribute.</p>
</dd>
</dl>
<dl class="idl" title="dictionary RTCAnswerOptions : RTCOfferAnswerOptions">
</dl>
</section>
</section>
<section>
<h3>RTCPeerConnection Interface</h3>
<p>The general operation of the RTCPeerConnection is described in
[[!JSEP]].</p>
<section>
<h4>Operation</h4>
<p>Calling <code>new <a>RTCPeerConnection</a>(<var>configuration</var>
)</code> creates an <code><a>RTCPeerConnection</a></code> object.</p>
<p>The <var>configuration</var> has the information to find and access
the servers used by ICE. There may be multiple servers of each type and
any TURN server also acts as a STUN server.</p>
<p>An <code><a>RTCPeerConnection</a></code> object has an associated
<dfn id="rtcpeerconnection-ice-agent">ICE agent</dfn> [[!ICE]],
<dfn>signaling state</dfn>, <dfn>ICE gathering state</dfn>, and <dfn>ICE
connection state</dfn>. These are initialized when the object is created.</p>
<p>When the <dfn id=
"dom-peerconnection"><code>RTCPeerConnection()</code></dfn> constructor
is invoked, the user agent MUST run the following steps:</p>
<ol>
<li>
<p>Let <var>connection</var> be a newly created
<code><a>RTCPeerConnection</a></code> object.</p>
</li>
<li>
<p><a href="#set-pc-configuration">Set the configuration</a>
specified by the constructor's first argument.</p>
</li>
<li>
<p>Create an ICE Agent as defined in [[!ICE]] and let
<var>connection</var>'s <code>RTCPeerConnection</code> ICE Agent be
that ICE Agent. The ICE Agent will
proceed with gathering as soon as the <a href=
"#ice-transports-setting">ICE transports setting</a> is not set to
<code>none</code>. At this point the ICE Agent does not know how
many ICE components it needs (and hence the number of candidates to
gather), but it can make a reasonable assumption such as 2. As the
<code>RTCPeerConnection</code> object gets more information, the
ICE Agent can adjust the number of components.</p>
</li>
<li>
<p>Set <var>connection</var>'s <a>
signaling state</a> to <code>stable</code>.</p>
</li>
<li>
<p>Set <var>connection</var>'s
<a>ICE connection state</a> to <code>new</code>.</p>
</li>
<li>
<p>Set <var>connection</var>'s <a>
ICE gathering state</a> to <code>new</code>.</p>
</li>
<li>
<p>Set <var>connection</var>'s
<code><a href=
"#dom-peerconnection-pendinglocaldesc">pendingLocalDescription</a></code>,
<code><a href=
"#dom-peerconnection-currentlocaldesc">currentLocalDescription</a></code>,
<code><a href=
"#dom-peerconnection-pendingremotedesc">pendingRemoteDescription</a></code>
and <code><a href=
"#dom-peerconnection-currentremotedesc">currentRemoteDescription</a></code>
to null.
</p>
</li>
<li>
<p>Initialize an internal variable <var>operations</var> to represent a queue of
operations with an empty array.</p>
</li>
<li>
<p>If the <code>certificates</code> value in
the <code>RTCConfiguration</code> structure is non-empty, check that
the <code>expires</code> on each value is in the future. If a
certificate has expired, throw an <code>InvalidAccessError</code>
exception and abort these steps; otherwise, store the certificates.
If no <code>certificates</code> value was specified, one or more
new <code>RTCCertificate</code> instances are generated for use with
this <code>RTCPeerConnection</code> instance.</p>
</li>
<li>
<p>Return <var>connection</var>.</p>
</li>
</ol>
<p>Once the RTCPeerConnection object has been initialized, for every
call to <code>createOffer</code>, <code>setLocalDescription</code>,
<code>createAnswer</code>, <code>setRemoteDescription</code>,
and <code>addIceCandidate</code>,
execute the following steps:</p>
<ol>
<li>
<p>Let <var>p</var> be a new promise.</p>
</li>
<li>
<p>Append an object representing the current call being handled
(i.e. function name and corresponding arguments) to the
<var>operations</var> array.</p>
</li>
<li>
<p>If the length of the <var>operations</var> array is exactly 1,
execute the object from the front of the queue.</p>
</li>
<li>
<p>Upon fulfillment or rejection of the promise returned
by the function, fulfill or reject <var>p</var> with the
corresponding value or reason. Upon fulfillment or
rejection of <var>p</var>, execute the following
steps:</p>
<ol>
<li><p>Remove the corresponding object from
the <var>operations</var> array.</p></li>
<li><p>If the array is non-empty, execute the first
object queued.</p></li>
</ol>
</li>
<li>
<p>Return <var>p</var>.</p>
</li>
</ol>
<p>The general idea is to have only one among <code>createOffer</code>,
<code>setLocalDescription</code>, <code>createAnswer</code> and
<code>setRemoteDescription</code>
and <code>addIceCandidate</code> executing at any given
time. If subsequent calls are made while the returned promise
of a previous call is still unsettled, they are added to a
queue and executed when all the previous calls are executed
and their promises are settled.</p>
<p>Additionally, during the lifetime of the RTCPeerConnection object,
the following procedures are followed when an ICE event occurs:</p>
<ol>
<li>
<p>If the <code>RTCPeerConnection</code>'s
<a>ICE gathering state</a> is <code>new</code> and the <a href=
"#ice-transports-setting">ICE transports setting</a> is not set to
<code>none</code>, the user agent MUST queue a task to start
gathering ICE addresses and <a>update the ICE gathering state</a>
to <code>gathering</code>.</p>
</li>
<li>
<p>If the ICE Agent has found one or more candidate pairs for each
<code>MediaStreamTrack</code> that forms a valid connection, <a>update the ICE connection
state</a> to <code>connected</code>.</p>
</li>
<li>
<p>When the ICE Agent finishes checking all candidate pairs, if at
least one connection has been found for each <a>media description</a>, <a>update the
ICE connection state</a> to <code>completed</code>, otherwise to
<code>failed</code>.</p>
</li>
</ol>
<p>When a new ICE candidate is available or when the ICE gathering process is done
, the user agent MUST queue a task to run the
following steps:</p>
<ol>
<li>
<p>Let <var>connection</var> be the
<code><a>RTCPeerConnection</a></code> object associated with this
ICE Agent.</p>
</li>
<li>
<p>If <var>connection</var>'s
<a>signaling state</a> is <code>closed</code>, abort these steps.</p>
</li>
<li>
<p>If the intent of the ICE Agent is to notify the script that:</p>
<ul>
<li>
<p>A new candidate is available.</p>
<p>Add the candidate to <var>connection</var>'s
<code><a>localDescription</a></code> and create a
<code><a>RTCIceCandidate</a></code> instance to represent the
candidate. Let <var>newCandidate</var> be that object.</p>
</li>
<li>
<p>The gathering process is done.</p>
<p><a data-lt="update the ICE gathering state">Update <var>connection</var>'s ICE gathering
state</a> to <code>completed</code> and let
<var>newCandidate</var> be null.</p>
</li>
</ul>
</li>
<li>
<p>Fire an event named <code><a href=
"#event-icecandidate">icecandidate</a></code> with
<var>newCandidate</var> at <var>connection</var>.</p>
</li>
</ol>
<p>To <dfn id=
"update-ice-gathering-state">update the <a>ICE gathering state</a></dfn> of an
<code><a>RTCPeerConnection</a></code> instance <var>connection</var> to
<var>newState</var>, the User Agent MUST queue a task that sets
<var>connection</var>'s <a href=
"#dom-peerconnection-ice-gathering-state">iceGatheringState</a>
attribute to <var>newState</var> and fires a simple event named
<code><a href=
"#event-icegatheringstatechange">icegatheringstatechange</a></code> at
<var>connection</var>.</p>
<p>To <dfn id=
"update-ice-connection-state">update the <a>ICE connection state</a></dfn> of an
<code><a>RTCPeerConnection</a></code> instance <var>connection</var> to
<var>newState</var>, the User Agent MUST queue a task that sets
<var>connection</var>'s <a href=
"#dom-peerconnection-ice-connection-state">iceConnectionState</a>
attribute to <var>newState</var> and fires a simple event named
<code><a href=
"#event-iceconnectionstatechange">icegatheringstatechange</a></code> at
<var>connection</var>.</p>
<p>To <dfn id="set-description">set an RTCSessionDescription</dfn>
<var>description</var> on an <code><a>RTCPeerConnection</a></code>
object <var>connection</var>, run the following steps:</p>
<ol>
<li>
<p>If <var>connection</var>'s
<a>signaling
state</a> is <code>closed</code>, the user agent MUST return a
promise rejected with an <code>InvalidStateError</code>.</p>
</li>
<li>
<p>Let <var>p</var> be a new promise.</p>
</li>
<li>
<p>In parallel, start the process to apply <var>description</var> as
described in <span data-jsep="processing-a-local-desc processing-a-remote-desc">[[!JSEP]]</span>.</p>
<ol>
<li>
<p>If the process to apply <var>description</var> fails for
any reason, then user agent MUST queue a task runs the
following steps:</p>
<ol>
<li>
<p>If <var>connection</var>'s <a>signaling state</a>
is <code>closed</code>, then abort these steps.</p>
</li>
<li>
<p>If the <var>description</var>'s <code><a href=
"#widl-RTCSessionDescription-type">type</a></code> is wrong for
the current <a>signaling state</a> of
<var>connection</var>, then reject <var>p</var> with a <code>InvalidStateError</code> and abort these steps.</p>
<p>If the content of <var>description</var> is invalid,
then reject <var>p</var> with an
<code>InvalidAccessError</code> and abort these
steps.</p>
</li>
<li>
<p>If <var>description</var> cannot be applied at the media
layer, but the User Agent recovered, possibly by rolling back
to the previous configuration, then reject <var>p</var> with
<code>OperationError</code> and abort
these steps.</p>
<p>This occurs, for example, when the version of
<var>description</var> is older than the one currently
being used.</p>
</li>
<li>
<p>Otherwise, set <var>connection</var>'s <a>signaling state</a> to
<code>closed</code>.</p>
</li>
<li>
<p>Fire a simple event named <code><a href=
"#event-signalingstatechange">signalingstatechange</a></code>
at <var>connection</var>.</p>
</li>
<li>
<p>Reject <var>p</var> with <code>OperationError</code>.</p>
</li>
</ol>
</li>
<li>
<p>If <var>description</var> is applied successfully, the user
agent MUST queue a task that runs the following steps:</p>
<ol>
<li>
<p>If <var>connection</var>'s <a>signaling state</a>
is <code>closed</code>, then abort these steps.</p>
</li>
<li>
<p>If <var>description</var> is set as a local description, and
its content matches the state of all tracks and data channels,
<a href="#clearing-negotiation-needed">as defined below</a>,
clear the negotiation-needed flag.
</p>
<p class="issue">NOTE: The principles of pending and current SDP
were agreed by the WG but the details in the next steps have not
yet been fully reviewed. TODO - review this.</p>
</li>
<li>
<p>If <var>description</var> is set as a local description,
then run one of the following steps:</p>
<ul>
<!-- A) transition stable to haveLocalOffer -->
<li>
<p>If <var>description</var> is of type "offer",
set <var>connection</var>'s <code><a href=
"#dom-peerconnection-pendinglocaldesc">pendingLocalDescription</a></code>
attribute to <var>description</var> and <a>signaling state</a>
to <code>have-local-offer</code>.</p>
</li>
<!-- C) transition haveRemoteOffer or haveLocalProvAnswer to
stable -->
<li>
<p>If <var>description</var> is
of type "answer", then this completes an offer answer
negotiation. Set <var>connection</var>'s <code><a href=
"#dom-peerconnection-currentlocaldesc">currentLocalDescription</a></code>
to <var>description</var> and <code><a href=
"#dom-peerconnection-currentremotedesc">currentRemoteDescription</a></code>
to the value of <code><a href=
"#dom-peerconnection-pendingremotedesc">pendingRemoteDescription</a></code>.
Set both <code><a href=
"#dom-peerconnection-pendingremotedesc">pendingRemoteDescription</a></code>
and <code><a href=
"#dom-peerconnection-pendinglocaldesc">pendingLocalDescription</a></code>
to null. Finally set <var>connection</var>'s <a>signaling state</a>
to <code>stable</code></p>
</li>
<!-- B) transition rollback to haveLocalOffer to stable -->
<li>
<p>If <var>description</var> is
of type "rollback", then this is a rollback. Set
<var>connection</var>'s <code><a href=
"#dom-peerconnection-pendinglocaldesc">pendingLocalDescription</a></code>
to null and <a>signaling state</a>
to <code>stable</code>.</p>
</li>
<!-- G) transition haveRemoteOffer to haveLocalProvAnswer -->
<li>
<p>If <var>description</var> is
of type "pranswer", then set <var>connection</var>'s
<code><a href=
"#dom-peerconnection-pendinglocaldesc">pendingLocalDescription</a></code>
to <var>description</var> and <a>signaling state</a>
to <code>have-local-pranswer</code>.</p>
</li>
</ul>
</li>
<li>
<p>Otherwise, if <var>description</var> is set as a remote
description, then run one of the following steps:</p>
<ul>
<!-- D) transition stable to haveRemoteOffer -->
<li>
<p>If <var>description</var> is
of type "offer",
set <var>connection</var>'s <code><a href=
"#dom-peerconnection-pendingremotedesc">pendingRemoteDescription</a></code>
attribute to <var>description</var> and <a>signaling state</a>
to <code>have-remote-offer</code>.</p>
</li>
<!-- F) transition haveRemoteOffer or haveLocalProvAnswer to
stable -->
<li>
<p>If <var>description</var> is
of type "answer", then this completes an offer answer
negotiation. Set <var>connection</var>'s <code><a href=
"#dom-peerconnection-currentremotedesc">currentRemoteDescription</a></code>
to <var>description</var> and <code><a href=
"#dom-peerconnection-currentlocaldesc">currentLocalDescription</a></code>
to the value of <code><a href=
"#dom-peerconnection-pendinglocaldesc">pendingLocalDescription</a></code>.
Set both <code><a href=
"#dom-peerconnection-pendingremotedesc">pendingRemoteDescription</a></code>
and <code><a href=
"#dom-peerconnection-pendinglocaldesc">pendingLocalDescription</a></code>
to null. Finally set <var>connection</var>'s <a>signaling state</a>
to <code>stable</code></p>
</li>
<!-- E) transition rollback to haveRemoteOffer to stable -->
<li>
<p>If <var>description</var> is
of type "rollback", then this is a rollback. Set
<var>connection</var>'s <code><a href=
"#dom-peerconnection-pendingremotedesc">pendingRemoteDescription</a></code>
to null and <a>signaling state</a>
to <code>stable</code>.</p>
</li>
<!-- H) transition haveRemoteOffer to haveLocalProvAnswer -->
<li>
<p>If <var>description</var> is
of type "pranswer", then set <var>connection</var>'s
<code><a href=
"#dom-peerconnection-pendingremotedesc">pendingRemoteDescription</a></code>
to <var>description</var> and <a>signaling state</a>
to <code>have-remote-pranswer</code>.</p>
</li>
</ul>
</li>
<li>
<p>If <var>connection</var>'s <a>signaling state</a>
changed above, fire a simple event named <code><a href=
"#event-signalingstatechange">signalingstatechange</a></code>
at <var>connection</var>.</p>
</li>
<li>
<p>If <var>description</var> is set as a local description,
<var>connection</var>'s <a>ICE gathering
state</a> is <code>new</code>, and <var>description</var>
contains media, then <a data-lt="update the ICE gathering state">update <var>connection</var>'s
ICE gathering state</a> to <code>gathering</code>.</p>
</li>
<li>
<p>If the process to apply <var>description</var> resulted
in an ICE restart <span data-jsep="applying-a-local-desc applying-a-remote-desc">[[!JSEP]]</span>, then run the following
steps:</p>
<ol>
<li>
<p>If <var>connection</var> is not already gathering,
<a data-lt="update the ICE gathering state">update
<var>connection</var>'s ICE gathering state</a> to
<code>gathering</code>.</p>
</li>
<li>
<p>If <var>connection</var>'s <a>
ICE connection state</a>
is <code>completed</code>, <a data-lt="update the ICE connection state">update
<var>connection</var>'s ICE connection state</a> to
<code>connected</code>.</p>
</li>
</ol>
</li>
<li>
<p>If <var>description</var> is set as a remote description
with new media descriptions [[!JSEP]], the User Agent
MUST <a href="#dispatch-receiver">dispatch a receiver</a> for
all new media descriptions.</p>
</li>
<li>
<p>If <var>connection</var>'s <a>signaling state</a> is
now <code>stable</code>, and the negotiation-needed flag is
set, the User Agent MUST queue a task to fire a simple event
named <code><a href=
"#event-negotiation">negotiationneeded</a></code> at
<var>connection</var> and clear the negotiation-needed flag.</p>
</li>
<li>
<p>Resolve <var>p</var> with <var>undefined</var>.</p>
</li>
</ol>
</li>
</ol>
</li>
<li>
<p>Return <var>p</var>.</p>
</li>
</ol>
<p>The task source for the tasks
listed in this section is the <a>networking task source</a>.</p>
</section>
<section>
<h3>Interface Definition</h3>
<p>The <code><a>RTCPeerConnection</a></code> interface presented in this
section is extended by several partial
interfaces throughout this specification. Notably, the <a href=
"#rtcpeerconnection-interface-extensions">RTP Media section</a>, that
adds the APIs to send and receive <code><a>MediaStreamTrack</a></code>
objects.</p>
<dl class="idl" title="interface RTCPeerConnection : EventTarget ">
<dt>Constructor (optional RTCConfiguration configuration)</dt>
<dd>
See the <a href="#dom-peerconnection">RTCPeerConnection constructor
algorithm</a>.
</dd>
<dt>Promise<RTCSessionDescription> createOffer (
optional RTCOfferOptions options)</dt>
<dd>
<p>The createOffer method generates a blob of SDP that contains an
RFC 3264 offer with the supported configurations for the session,
including descriptions of the local <code>MediaStreamTrack</code>s
attached to this <code>RTCPeerConnection</code>, the codec/RTP/RTCP
options supported by this implementation, and any candidates that
have been gathered by the ICE Agent. The <code>options</code> parameter may be
supplied to provide additional control over the offer
generated.</p>
<p>As an offer, the generated SDP will contain the full set of
capabilities supported by the session (as opposed to an answer,
which will include only a specific negotiated subset to use); for
each SDP line, the generation of the SDP MUST follow the
appropriate process for generating an offer. In the event
<code>createOffer</code> is called after the session is established, <code>createOffer</code>
will generate an offer that is compatible with the current session,
incorporating any changes that have been made to the session since
the last complete offer-answer exchange, such as addition or
removal of tracks. If no changes have been made, the offer will
include the capabilities of the current local description as well
as any additional capabilities that could be negotiated in an
updated offer.</p>
<p>Session descriptions generated by <code>createOffer</code> MUST be
immediately usable by <code>setLocalDescription</code> without causing an error
as long as <code>setLocalDescription</code> is called reasonably soon.
If a system has limited resources (e.g. a finite number
of decoders), <code>createOffer</code> needs to return an offer that reflects
the current state of the system, so that <code>setLocalDescription</code> will
succeed when it attempts to acquire those resources. The session
descriptions MUST remain usable by <code>setLocalDescription</code> without
causing an error until at least the end of the fulfillment callback of the
returned promise. Calling this method is needed to get the ICE user name
fragment and password.</p>
<p>The value for <code>certificates</code> in
the <code><a>RTCConfiguration</a></code> for
the <code>RTCPeerConnection</code> is used to produce a set of
certificate fingerprints. These certificate fingerprints are used
in the construction of SDP and as input to requests for identity
assertions.</p>
<p>If the <code>RTCPeerConnection</code> is configured to generate
Identity assertions by calling <code>setIdentityProvider</code>, then the
session description SHALL contain an appropriate assertion. If the
identity provider is unable to produce an identity assertion, the
call to <code>createOffer</code> MUST be rejected with a