Editorial review and consistency check; moved voice chat scenarios from XEP-0166 to this specification.
&xep0166; can be used to initiate and negotiate a wide range of peer-to-peer sessions. One session type of interest is audio chat. This document specifies a format for negotiating Jingle audio sessions over the Realtime Transport Protocol (RTP; see &rfc3550;).
The Jingle content description format defined herein is designed to meet the following requirements:
+The Jingle application format defined herein is designed to meet the following requirements:
In accordance with Section 8 of XEP-0166, this document specifies the following information related to the Jingle Audio via RTP application type:
The content negotiation process is defined in the Negotiating a Jingle Audio Session section of this document.
The semantics of the &DESCRIPTION; element are defined in the Content Description Format section of this document.
The application format negotiation process is defined in the Negotiating a Jingle Audio Session section of this document.
The semantics of the &DESCRIPTION; element are defined in the Application Format section of this document.
A mapping of Jingle semantics to the Session Description Protocol is provided in the Mapping to Session Description Protocol section of this document.
A Jingle audio session SHOULD use a lossy transport method such as &xep0177; or the "ice-udp" method specified in &xep0176;, but MAY use a reliable transport such as "ice-tcp".
A Jingle audio session is described by one or more encodings contained within a wrapper <description/> element. In the language of RFC 4566 these encodings are payload-types; therefore, each <payload-type/> element specifies an encoding that can be used for the audio stream. In Jingle Audio, these encodings are used in the context of RTP. The most common encodings for the Audio/Video Profile (AVP) of RTP are listed in &rfc3551; (these "static" types are reserved from payload ID 0 through payload ID 95), although other encodings are allowed (these "dynamic" types use payload IDs 96 to 127) in accordance with the dynamic assignment rules described in Section 3 of RFC 3551.
+A Jingle audio session is described by a content type that contains one application format and one transport method. The application format consists of one or more encodings contained within a wrapper <description/> element qualified by the 'http://www.xmpp.org/extensions/xep-0167.html#ns' namespace &NSNOTE;. In the language of RFC 4566 these encodings are payload-types; therefore, each <payload-type/> element specifies an encoding that can be used for the audio stream. In Jingle Audio, these encodings are used in the context of RTP. The most common encodings for the Audio/Video Profile (AVP) of RTP are listed in &rfc3551; (these "static" types are reserved from payload ID 0 through payload ID 95), although other encodings are allowed (these "dynamic" types use payload IDs 96 to 127) in accordance with the dynamic assignment rules described in Section 3 of RFC 3551.
The allowable attributes are as follows:
The encodings SHOULD be provided in order of preference.
-The <description/> element is intended to be a child of a &JINGLE; element as specified in XEP-0166.
+The &DESCRIPTION; element is intended to be a child of a &JINGLE; element as specified in XEP-0166.
+The encodings SHOULD be provided in order of preference by placing the most-preferred &PAYLOADTYPE; element as the first child of the &DESCRIPTION; element (etc.).
Each <payload-type/> element MAY contain one or more child elements that specify particular parameters related to the payload. For example, as described in &rtpspeex;, the "cng", "mode", and "vbr" parameters may be specified in relation to usage of the Speex
@@ -202,7 +209,7 @@
When the initiator sends a session-initiate stanza to the receiver, the &DESCRIPTION; element includes all of the payload types that the initiator can receive for Jingle audio (each one encapsulated in a separate &PAYLOADTYPE; element):
-Upon receiving the session-initiate stanza, the receiver determines whether it can provisionally accept the session and proceed with the negotiation. The general Jingle error cases are specified in XEP-0166. In addition, the receiver must determine if it supports any of the payload types advertised by the initiator; if it does not, it MUST reject the session by sending a <unsupported-codecs/> error:
-If there is no error, the receiver provisionally accepts the session:
-The receiver then should send a list of the payload types that it can receive via a Jingle "content-accept" (or "session-accept") action. The list that the receiver sends MAY include any payload types (not a subset of the payload types sent by the initiator) but SHOULD retain the ID numbers and order specified by the initiator.
-The initiator acknowledges the 'content-accept' with an empty IQ result:
-After successful transport negotiation (not shown here), the receiver then accepts the session:
-And the initiator acknowledges session acceptance:
-Note: Because a "session-accept" action implicitly indicates acceptance of the application format (i.e., "content-accept"), it is not necessary to send a separate "content-accept" action. This flow is shown for completeness only.
The following sections show a number of Jingle audio scenarios, in relative order of complexity.
+In this scenario, Romeo initiates a voice chat with Juliet but she is otherwise engaged.
+The session flow is as follows:
+|
+ | error |
+ | (recipient-unavailable) |
+ |<----------------------------|
+ ]]>
+ The protocol flow is as follows.
+In this scenario, Romeo initiates a voice chat with Juliet using a transport method of ICE-UDP. The parties also exchange informational messages.
+The session flow is as follows:
+|
+ | ack |
+ |<----------------------------|
+ | session-info (ringing) |
+ |<----------------------------|
+ | ack |
+ |---------------------------->|
+ | transport-info (X times) |
+ | (with acks) |
+ |<--------------------------->|
+ | session-accept |
+ |<----------------------------|
+ | ack |
+ |---------------------------->|
+ | AUDIO (RTP) |
+ |<===========================>|
+ | session-terminate |
+ |<----------------------------|
+ | ack |
+ |---------------------------->|
+ | |
+ ]]>
+ The protocol flow is as follows.
+For each candidate received, the other party acknowledges receipt or returns an error:
+At the same time (i.e., immediately after provisionally accepting the session, not waiting for the initiator to begin or finish sending candidates), the responder also begins sending candidates that may work for it. As above, the initiator acknowledges receipt of the candidates.
+As the initiator and responder receive candidates, they probe the various candidate transports for connectivity. In performing these connectivity checks, the parties follow the procedure specified in Section 7 of draft-ietf-mmusic-ice.
+If one of the candidate transports is found to work, the receiver accepts the session.
+If the payload types and transport candidate can be successfully used by both parties, then the initiator acknowledges the session-accept.
+The parties now begin to exchange media. In this case they would exchange audio using the Speex codec at a clockrate of 8000 since that is the highest-priority codec for the responder (as determined by the XML order of the &PAYLOADTYPE; children).
+The parties may continue the session as long as desired.
+Eventually, one of the parties terminates the session.
+The other party then acknowledges termination of the session:
+In this scenario, Romeo initiates a combined audio and video chat with Juliet using a transport method of ICE. Juliet at first refuses the video portion, then later offers to add video, which Romeo accepts. The parties also exchange various informational messages
+The session flow is as follows:
+|
+ | ack |
+ |<----------------------------|
+ | session-info (ringing) |
+ |<----------------------------|
+ | ack |
+ |---------------------------->|
+ | content-remove |
+ |<----------------------------|
+ | ack |
+ |---------------------------->|
+ | content-accept |
+ |---------------------------->|
+ | ack |
+ |<----------------------------|
+ | transport-info (X times) |
+ | (with acks) |
+ |<--------------------------->|
+ | session-accept |
+ |<----------------------------|
+ | ack |
+ |---------------------------->|
+ | AUDIO (RTP) |
+ |<===========================>|
+ | session-info (hold) |
+ |<----------------------------|
+ | ack |
+ |---------------------------->|
+ | session-info (active) |
+ |<----------------------------|
+ | ack |
+ |---------------------------->|
+ | content-add |
+ |<----------------------------|
+ | ack |
+ |---------------------------->|
+ | content-accept |
+ |---------------------------->|
+ | ack |
+ |<----------------------------|
+ | AUDIO + VIDEO (RTP) |
+ |<===========================>|
+ | session-terminate |
+ |<----------------------------|
+ | ack |
+ |---------------------------->|
+ | |
+ ]]>
+ The protocol flow is as follows.
+However, Juliet doesn't want to do video because she is having a bad hair day, so she sends a "content-remove" request to Romeo.
+Romeo then acknowledges the content-remove request and, if it is acceptable, returns a content-accept:
+The other party then acknowledges the acceptance.
+As in the previous scenario, the parties exchange ICE candidates (see above for examples).
+Once the parties find candidate transports that work, the receiver accepts the session.
+As above, if the payload types and transport candidate can be successfully used by both parties, then the initiator acknowledges the session-accept.
+The parties now begin to exchange media. In this case they would exchange audio using the Speex codec at a clockrate of 8000 since that is the highest-priority codec for the responder (as determined by the XML order of the &PAYLOADTYPE; children).
+Juliet wants to get her hair in order so she puts Romeo on hold.
+Juliet returns so she informs Romeo that she is actively engaged in the call again.
+The parties now continue the audio chat.
+Finally Juliet decides that she is presentable for a video chat so she sends a content-add request to Romeo.
+The entity receiving the content-add request then acknowledges the request and, if it is acceptable, returns a content-accept:
+The other party then acknowledges the acceptance.
+The media session proceeds. Now they would exchange both audio and video, where the audio is exchanged the Speex codec at a clockrate of 8000 and the video is exchanged using the Theora codec with a height of 720 pixels, a width of 1280 pixels, and so on.
+The parties may continue the session as long as desired.
+Eventually, one of the parties terminates the session.
+In this scenario, Romeo initiates a voice chat with Juliet using a transport method of ICE-UDP and an unencrypted profile of "RTP/AVP", but Juliet wants to chat securely so she requests the use of a secure transport as specified in &sdpdtls; (via a profile of "UDP/TLS/RTP/AVP").
+The session flow is as follows:
+|
+ | ack |
+ |<----------------------------|
+ | session-info (ringing) |
+ |<----------------------------|
+ | ack |
+ |---------------------------->|
+ | content-modify |
+ |<----------------------------|
+ | ack |
+ |---------------------------->|
+ | content-accept |
+ |---------------------------->|
+ | ack |
+ |<----------------------------|
+ | transport-info (X times) |
+ | (with acks) |
+ |<--------------------------->|
+ | session-accept |
+ |<----------------------------|
+ | ack |
+ |---------------------------->|
+ | AUDIO (RTP) |
+ |<===========================>|
+ | session-terminate |
+ |<----------------------------|
+ | ack |
+ |---------------------------->|
+ | |
+ ]]>
+ The protocol flow is as follows.
+However, Juliet wants to make sure that the communications are encrypted, so she sends a "content-modify" request to Romeo.
+Romeo then acknowledges the content-modify request and, if it is acceptable, returns a content-accept:
+The other party then acknowledges the acceptance.
+As in the previous scenario, the parties exchange ICE candidates (see above for examples).
+If one of the candidate transports is found to work, the receiver accepts the session.
+If the payload types and transport candidate can be successfully used by both parties, then the initiator acknowledges the session-accept.
+The parties now begin to exchange media. In this case they would exchange audio using the Speex codec at a clockrate of 8000 since that is the highest-priority codec for the responder (as determined by the XML order of the &PAYLOADTYPE; children).
+The parties may continue the session as long as desired.
+Eventually, one of the parties terminates the session.
+The other party then acknowledges termination of the session:
+If the payload type is static (payload-type IDs 0 through 95 inclusive), it MUST be mapped to a media field defined in RFC 4566. The generic format for the media field is as follows:
]]>
- In the context of Jingle audio sessions, the <media> is "audio", the <port> is the preferred port for such communications (which may be determined dynamically), the <transport> is whatever transport method is negotiated via the Jingle negotiation (e.g., "RTP/AVT"), and the <fmt list> is the payload-type ID.
+In the context of Jingle audio sessions, the <media> is "audio", the <port> is the preferred port for such communications (which may be determined dynamically), the <transport> is whatever profile is negotiated via the 'profile' attribute of the &CONTENT; element in the Jingle negotiation (e.g., "RTP/AVT"), and the <fmt list> is the payload-type ID.
For example, consider the following static payload-type:
-If the payload type is dynamic (payload-type IDs 96 through 127 inclusive), it SHOULD be mapped to an SDP media field plus an SDP attribute field named "rtpmap".
For example, consider a payload of 16-bit linear-encoded stereo audio sampled at 16KHz associated with dynamic payload-type 96:
-As noted, if additional parameters are to be specified, they shall be represented as attributes of the <payload-type/> element of the child <parameter/> element, as in the following example.
-The Jingle Audio-specific error conditions are as follows:
+The Jingle-Audio-specific error conditions are as follows:
| Jingle Condition | +Jingle Audio Condition | XMPP Condition | Description |
|---|