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---
title: RTCSessionDescription
slug: Web/API/RTCSessionDescription
tags:
- API
- Audio
- Experimental
- Interface
- Media
- NeedsTranslation
- Reference
- TopicStub
- Video
- Web
- WebRTC
translation_of: Web/API/RTCSessionDescription
---
<p>{{APIRef("WebRTC")}}{{SeeCompatTable}}</p>
<p>The <strong><code>RTCSessionDescription</code></strong> interface describes one end of a connection—or potential connection—and how it's configured. Each <code>RTCSessionDescription</code> consists of a description {{domxref("RTCSessionDescription.type", "type")}} indicating which part of the offer/answer negotiation process it describes and of the {{Glossary("SDP")}} descriptor of the session.</p>
<p>The process of negotiating a connection between two peers involves exchanging <code>RTCSessionDescription</code> objects back and forth, with each description suggesting one combination of connection configuration options that the sender of the description supports. Once the two peers agree upon a configuration for the connection, negotiation is complete.</p>
<h2 id="Properties">Properties</h2>
<p><em>The <code>RTCSessionDescription</code> interface doesn't inherit any properties.</em></p>
<dl>
<dt>{{domxref("RTCSessionDescription.type")}} {{ReadOnlyInline}}</dt>
<dd>An enum of type <code>{{anch("RTCSdpType")}}</code> describing the session description's type.</dd>
</dl>
<dl>
<dt>{{domxref("RTCSessionDescription.sdp")}} {{ReadOnlyInline}}</dt>
<dd>A {{domxref("DOMString")}} containing the {{Glossary("SDP")}} describing the session.</dd>
</dl>
<h2 id="Constants">Constants</h2>
<h3 id="RTCSdpType">RTCSdpType</h3>
<p>This enum defines strings that describe the current state of the session description, as used in the {{domxref("RTCSessionDescription.type", "type")}} property. The session description's type will be specified using one of these values.</p>
<table class="standard-table">
<thead>
<tr>
<th scope="col">Value</th>
<th scope="col">Description</th>
</tr>
</thead>
<tbody>
<tr>
<td><code>answer</code></td>
<td>The SDP contained in the {{domxref("RTCSessionDescription.sdp", "sdp")}} property is the definitive choice in the exchange. In other words, this session description describes the agreed-upon configuration, and is being sent to finalize negotiation.</td>
</tr>
<tr>
<td><code>offer</code></td>
<td>The session description object describes the initial proposal in an offer/answer exchange. The session negotiation process begins with an offer being sent from the caller to the callee.</td>
</tr>
<tr>
<td><code>pranswer</code></td>
<td>The session description object describes a provisional answer; that is, a response to a previous offer that is not the final answer. It is usually employed by legacy hardware.</td>
</tr>
<tr>
<td><code>rollback</code></td>
<td>This special type with an empty session description is used to roll back to the previous stable state.</td>
</tr>
</tbody>
</table>
<h2 id="Methods">Methods</h2>
<p><em>The <code>RTCSessionDescription</code> doesn't inherit any methods.</em></p>
<dl>
<dt>{{domxref("RTCSessionDescription.RTCSessionDescription", "RTCSessionDescription()")}} {{deprecated_inline}}</dt>
<dd>This constructor returns a new <code>RTCSessionDescription</code>. The parameter is a <code>RTCSessionDescriptionInit</code> dictionary containing the values to assign the two properties.</dd>
<dt>{{domxref("RTCSessionDescription.toJSON()")}}</dt>
<dd>Returns a {{Glossary("JSON")}} description of the object. The values of both properties, {{domxref("RTCSessionDescription.type", "type")}} and {{domxref("RTCSessionDescription.sdp", "sdp")}}, are contained in the generated JSON.</dd>
</dl>
<h2 id="Example">Example<span id="cke_bm_72C" style="display: none;"> </span></h2>
<pre class="brush: js">signalingChannel.onmessage = function (evt) {
if (!pc)
start(false);
var message = JSON.parse(evt.data);
if (message.sdp)
pc.setRemoteDescription(new RTCSessionDescription(message), function () {
// if we received an offer, we need to answer
if (pc.remoteDescription.type == "offer")
pc.createAnswer(localDescCreated, logError);
}, logError);
else
pc.addIceCandidate(new RTCIceCandidate(message.candidate),
function () {}, logError);
};
</pre>
<h2 id="Specifications">Specifications</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">Specification</th>
<th scope="col">Status</th>
<th scope="col">Comment</th>
</tr>
<tr>
<td>{{ SpecName('WebRTC 1.0', '#rtcsessiondescription-class', 'RTCSessionDescription') }}</td>
<td>{{Spec2('WebRTC 1.0')}}</td>
<td>Initial definition.</td>
</tr>
</tbody>
</table>
<h2 id="Browser_compatibility">Browser compatibility</h2>
<p>{{Compat("api.RTCSessionDescription")}}</p>
<h2 id="See_also">See also</h2>
<ul>
<li><a href="/en-US/docs/Web/Guide/API/WebRTC" title="/en-US/docs/CSS/Using_CSS_animations">WebRTC</a></li>
<li>{{domxref("RTCPeerConnection.setLocalDescription()")}} and {{domxref("RTCPeerConnection.setRemoteDescription()")}}</li>
</ul>
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