<abstract>This specification defines an XMPP protocol extension for initiating and managing peer-to-peer media sessions between two XMPP entities in a way that is interoperable with existing Internet standards. The protocol provides a pluggable model that enables the core session management semantics (compatible with SIP) to be used for a wide variety of application types (e.g., voice chat, video chat, file transfer) and with a wide variety of transport methods (e.g., TCP, UDP, ICE, application-specific transports).</abstract>
<li>Added cancel, expired, gone, security-error, and timeout reason conditions.</li>
<li>Changed XMPP error condition for Jingle <unknown-session/> condition from <bad-request/> to <item-not-found/>.</li>
<li>Changed XMPP error condition for Jingle tie breaks from <unexpected-request/> to <conflict/> and defined Jingle-specific condition of <tie-break/>.</li>
<remark><p>Added content-reject action to mirror content-accept for replies to content-add; also added transport-reject action to mirror transport-accept for replies to transport-replace.</p></remark>
<li>Changed "reliable" vs. "lossy" to "streaming" vs. "datagram", since reliability or dependability is orthogonal to the streaming nature of the transport.</li>
<li>Added "transport-replace" action (answered by "transport-accept").</li>
<li>Removed <condition/> element as container for Jingle condition elements inside <reason/>, since it introduced an unnecessary layer of indirection.</li>
<li>Modified state machine to allow content removal during PENDING state.</li>
<li>Noted that a session can have more than one content instance of the same type.</li>
<li>Noted that the 'name' attribute is unique to a creator.</li>
<li>Changed examples to once again use voice chat instead of file transfer.</li>
<remark><p>Updated examples to track changes to XEP-0167 and retraction of XEP-0180; corrected definition of name attribute to allow semantic meaning.</p></remark>
<remark><p>More clearly specified the content-replace action (essentially similar to content-add); specified that content-accept shall be sent in response to content-replace; removed content-modify and content-accept from PENDING state; adjusted text regarding initial session negotiation.</p></remark>
<remark><p>Added content-replace action; modified reasoncode and reasontext to use elements instead of attributes; added sid element to handle alternative-session condition; modified examples to use file transfer instead of voice chat; moved profile element to XEP-0167 and XEP-0180.</p></remark>
<remark><p>Removed content-accept after content-remove; removed errors for unsupported-content and unsupported-transports since they are handled via session-terminate; clarified handling of responder attribute.</p></remark>
<remark><p>Modified session flows for busy, unsupported application formats, and unsupported transport methods to enable separation between Jingle core and distinct modules for applications and transports; moved resource determination recommendations to XEP-208.</p></remark>
<remark><p>Added scenario for handling of busy state, including Jingle-specific error code and modified error flow (no longer an instance of decline).</p></remark>
<remark><p>Added scenarios for various session flows; clarified handling of content-add, content-modify, and content-remove actions; clarified rules for codec priority.</p></remark>
<remark><p>Simplified signalling process and state chart; Removed session-redirect action (use redirect error instead); removed content-decline action; removed transport-* actions (except transport-info for ICE negotiation); removed description-* actions; simplified syntax to allow only one transport per content type; corrected syntax of creator attribute to be either initiator or responder (not JIDs); added profile attribute to content element in order to specify RTP profile in use.</p></remark>
<remark><p>Added creator attribute to content element for prevention of race condition; modified spec to use provisional namespace before advancement to Draft (per XEP-0053).</p></remark>
<remark><p>Made several corrections to the state machines and examples.</p></remark>
</revision>
<revision>
<version>0.9</version>
<date>2006-09-08</date>
<initials>ram/psa</initials>
<remark><p>Further cleaned up state machines and state-related actions.</p></remark>
</revision>
<revision>
<version>0.8</version>
<date>2006-08-23</date>
<initials>ram/psa</initials>
<remark><p>Changed channels to components in line with ICE; changed various action names for consistency; added session-extend and session-reduce actions to add and remove description/transport pairs; added description-modify action; added sender attribute to specify directionality.</p></remark>
</revision>
<revision>
<version>0.7</version>
<date>2006-07-17</date>
<initials>psa</initials>
<remark><p>Added implementation note about handling multiple content types.</p></remark>
</revision>
<revision>
<version>0.6</version>
<date>2006-07-12</date>
<initials>se/psa</initials>
<remark><p>Changed media type to content type.</p></remark>
</revision>
<revision>
<version>0.5</version>
<date>2006-03-20</date>
<initials>psa/jb</initials>
<remark><p>Further clarified state machine diagrams; specified that session accept must include agreed-upon media format and transport description; moved deployment notes to appropriate transport spec.</p></remark>
<remark><p>Provided more detail about modify scenarios; defined media-specific and transport-specific actions and adjusted state machine accordingly.</p></remark>
</revision>
<revision>
<version>0.2</version>
<date>2006-02-13</date>
<initials>psa/jb</initials>
<remark><p>Per agreement among the co-authors, moved transport definition to separate specification, simplified state machine, and made other associated changes to the text, examples, and schemas; also harmonized redirect, decline, and terminate processes.</p></remark>
<remark><p>Restructured document flow; provided example of burst mode.</p></remark>
</revision>
<revision>
<version>0.0.8</version>
<date>2005-12-05</date>
<initials>psa/sl/jb</initials>
<remark><p>Distinguished between dribble mode and burst mode, including mode attribute, service discovery features, and implementation notes; provided detailed resource discovery examples; corrected state chart; specified session termination; specified error conditions; specified semantics of informational messages; began to define security considerations; added Joe Beda as co-author.</p></remark>
</revision>
<revision>
<version>0.0.7</version>
<date>2005-11-08</date>
<initials>psa</initials>
<remark><p>Added more detail to basic session flow; harmonized candidate negotiation process with ICE.</p></remark>
<p>The purpose of Jingle is to enable one-to-one, peer-to-peer media sessions between XMPP entities, where the negotiation occurs over the XMPP "channel" and the media is exchanged outside the XMPP channel using technologies such as the Real-time Transport Protocol (RTP; &rfc3550;), the User Datagram Protocol (UDP; &rfc0768;), and &ice;.</p>
<p>One target application for Jingle is simple voice and video chat (see &xep0167;). We stress the word "simple". The purpose of the core Jingle technology is not to build a full-fledged telephony application that supports call waiting, call forwarding, call transfer, hold music, IVR systems, find-me-follow-me functionality, conference calls, and the like. These features are of interest to some user populations, but adding support for them to the core Jingle layer would introduce unnecessary complexity into a technology that is designed for basic multimedia interaction.</p>
<p>In addition, the purpose of Jingle is not to supplant or replace existing Internet technologies based on the Session Initiation Protocol (SIP; &rfc3261;). Because dual-stack XMPP+SIP clients are difficult to build, Jingle was designed as a pure XMPP signalling protocol. However, Jingle is at the same time designed to interwork with SIP so that the millions of deployed XMPP clients can be added onto existing Voice over Internet Protocol (VoIP) networks, rather than limiting XMPP users to a separate and distinct network.</p>
<p>Jingle is designed in a modular way so that developers can easily add support for multimedia session types other than voice and video chat, such as application sharing, file transfer, collaborative editing, whiteboarding, and torrent broadcasting. The transport methods are also modular, so that Jingle implementations can use any appropriate media transport (including proprietary methods not standardized through the XMPP Standards Foundation).</p>
<p>In essence, Jingle enables two XMPP entities (e.g., romeo@montague.lit and juliet@capulet.lit) to set up, manage, and tear down a multimedia session. The negotiation takes place over XMPP, and the media transfer typically takes place outside of XMPP. A simplified session flow would be as follows: <note>Naturally, more complex scenarios are possible; such scenarios are described in other specifications, such as <cite>XEP-0167</cite> for voice and video chat.</note></p>
<p>To illustrate the basic flow, we show a truncated example with a "stub" application format and transport method (skipping non-essential steps to enforce the most important concepts).</p>
<p>After the responder acknowledges receipt of the session-initiate and the parties negotiate some parameters (not shown here), the responder would eventually send a session-accept to the initiator.</p>
<examplecaption="Responder definitively accepts the session"><![CDATA[
<p>The initiator acknowledges receipt of the session-accept (not shown here) and the parties can exchange "stub" media data over the "stub" transport.</p>
<p>Eventually, one of the parties (here the responder) will terminate the session.</p>
<examplecaption="Responder terminates the session"><![CDATA[
<iqfrom='juliet@capulet.lit/balcony'
id='term1'
to='romeo@montague.lit/orchard'
type='set'>
<jinglexmlns='urn:xmpp:jingle:0'
action='session-terminate'
initiator='romeo@montague.lit/orchard'
sid='a73sjjvkla37jfea'>
<reason>
<success/>
</reason>
</jingle>
</iq>
]]></example>
<p>The recipient acknowledges receipt of the session-terminate (not shown here) and the session is ended.</p>
<p>We now "fill in the blanks" for the &DESCRIPTION; and &TRANSPORT; elements with a more complex example: a voice chat session, where application type is a Jingle RTP session (with several different codec possibilities) and the transport method is &xep0176;.</p>
<p>Upon receiving the session-initiate stanza, the responder determines whether it can proceed with the negotiation. If there is no error, the responder acknowledges the session initiation request.</p>
<p>After successful transport negotiation (not shown here), the responder accepts the session by sending a session-accept action to the initiator (including the negotiated transport details and the subset of offered codecs that the responder supports).</p>
<li>Make it relatively easy to implement support for the protocol in standard Jabber/XMPP clients.</li>
<li>Where communication with non-XMPP entities is needed, push as much complexity as possible onto server-side gateways between the XMPP network and the non-XMPP network.</li>
</ol>
<p>This document defines the signalling protocol only. Additional documents specify the following:</p>
<li><p>Various application formats (audio, video, etc.) and, where possible, mapping of those types to the Session Description Protocol (SDP; see &rfc4566;); examples include <cite>Jingle RTP Sessions</cite> and &xep0234;.</p></li>
<li><p>Various transport methods; examples include <cite>Jingle ICE-UDP Transport</cite> and &xep0177;.</p></li>
<li><p>Procedures for mapping the Jingle signalling protocol to existing signalling standards such as the IETF's Session Initiation Protocol (SIP) and the ITU's H.323 protocol (see &h323;); see for example &xmppsipmedia;.</p></li>
<td>The data format of the content type being established, which formally declares one purpose of the session (e.g., "audio" or "video"). This is the 'what' of the session (i.e., the bits to be transferred), such as the acceptable codecs when establishing a voice conversation. In Jingle XML syntax the application format is the namespace of the &DESCRIPTION; element.</td>
<td>A numbered stream of data that needs to be transmitted between the endpoints for a given content type in the context of a given session. It is up to the transport to negotiate the details of each component. Depending on the content type, multiple components might be needed (e.g., one to transmit an RTP stream and another to transmit RTCP timing information).</td>
<td>One or more content types negotiated between two entities. It is delimited in time by a session-initiate action and a session-terminate action. During the lifetime of a session, content types can be added or removed. A session consists of at least one content type at a time.</td>
<td>The method for establishing data stream(s) between entities. Possible transports might include ICE-UDP, ICE-TCP, Raw UDP, inband data, etc. This is the 'how' of the session. In Jingle XML syntax this is the namespace of the &TRANSPORT; element. The transport method defines how to transfer bits from one host to another. Each transport method MUST specify whether it is datagram (thus suitable for applications where some packet loss is tolerable) or streaming (thus suitable for applications where packet loss is not tolerable).</td>
<li>Double-dashed lines (===) represent media packets that are sent via the media channel, which typically is not an XMPP channel but a direct or mediated channel between the endpoints.</li>
<p>This document defines the semantics and syntax for overall session management. It also provides pluggable "slots" for application formats and transport methods, which are specified in separate documents.</p>
<li>The parties attempt to set up data transmission over the designated transport method as defined in the relevant specification, which might involve the exchange of transport-info actions.</li>
<li>Optionally, either party can send session-info actions (to inform the other party that it is attempting transport negotiation, that its device is ringing, etc.).</li>
<p>After the initial session negotiation has been completed and the session is in the ACTIVE state, the parties can adjust the session definition by sending additional Jingle actions, such as content-modify, content-remove, content-add, description-info, and transport-replace. In addition, certain transport methods allow continued sending of transport-info actions while in the ACTIVE state. And naturally the parties can send session-info actions at any time.</p>
<p>The actions related to management of the overall Jingle session are as follows (detailed definitions are provided in under <linkurl='#def-action'>Action Attribute</link>).</p>
<ul>
<li>content-accept -- Accept a content-add action received from another party.</li>
<li>content-add -- Add one or more new content definitions to the session.</li>
<li>content-modify -- Change the directionality of media sending.</li>
<p>This section defines the high-level flow of a Jingle session. More detailed descriptions are provided in the specifications for Jingle application formats and transport methods.</p>
<p>In order to initiate a Jingle session, the initiator needs to determine which of the responder's XMPP resources is best for the desired application format. Methods for doing so are out of scope for this specification. However, see the <linkurl='#support'>Determining Support</link> section of this document (and associated specifications) for relevant information.</p>
<p>Once the initiator has discovered which of the responder's XMPP resources is ideal for the desired application format, it sends a session initiation request to the responder. This request is an IQ-set containing a &JINGLE; element qualified by the 'urn:xmpp:jingle:0' namespace &VNOTE;, where the value of the 'action' attribute is "session-initiate" and where the &JINGLE; element contains one or more &CONTENT; elements. Each &CONTENT; element defines a content type to be transferred during the session, and each &CONTENT; element in turn contains one &DESCRIPTION; child element that specifies a desired application format and one &TRANSPORT; child element that specifies a potential transport method. If either party wishes to propose the use of multiple transport methods for the same application format, it MUST include multiple &CONTENT; elements.</p>
<p>Note: The syntax and semantics of the &DESCRIPTION; and &TRANSPORT; elements are out of scope for this document, since they are defined in related specifications. The syntax and semantics of the &JINGLE; and &CONTENT; elements are specified in this document under <linkurl='#def'>Formal Definition</link>.</p>
<p>However, after acknowledging the session initiation request, the responder might subsequently determine that it cannot proceed with negotiation of the session (e.g., because it does not support any of the offered application formats or transport methods, because a human user is busy or unable to accept the session, because a human user wishes to formally decline the session, etc.). In these cases, the responder SHOULD immediately acknowledge the session initiation request but then terminate the session with an appropriate reason as described in the <linkurl='#session-terminate'>Termination</link> section of this document.</p>
<p>If the initiator is unknown to the responder (e.g., via presence subscription as defined in &rfc3921;) and the responder has a policy of not communicating via Jingle with unknown entities, it MUST return a &unavailable; error.</p>
<p>In general, negotiation will be necessary before the parties can agree on an acceptable set of application formats and transport methods. There are many potential parameter combinations, as defined in the relevant specifications for various application formats and transport methods.</p>
<p>If (after negotiation of transport methods and application formats as well as checking of transport candidates) the responder determines that it will be able to establish a connection, it sends a definitive acceptance to the initiator.</p>
<pclass='box'>Note: The protocol-level "session-accept" action is not to be confused with an interface-level acceptance of the session request. After receiving and acknowledging the "session-initiate" action received from the initiator, the responder's client SHOULD present an interface element that enables a human user to explicitly agree to proceeding with the session (e.g., an "Accept Incoming Call?" pop-up window including "Yes" and "No" buttons). However, the responder's client SHOULD NOT return a "session-accept" action to the initiator until the responder has explicitly agreed to proceed with the session (unless the initiator is on a list of entities whose sessions are automatically accepted).</p>
<p>The initiator then acknowledges the responder's definitive acceptance, after which the parties can exchange media over the negotiated connection.</p>
<p>If one of the parties cannot find a suitable transport method or candidate, it SHOULD terminate the session as described below.</p>
</section2>
<section2topic='Modifying an Active Session'anchor='session-modify'>
<p>Once a session is in the ACTIVE state, it might be modified via a content-add, content-modify, content-remove, or transport-info action. Examples of such modifications are shown in the specifications for various application formats and transport methods.</p>
<p>In order to gracefully end the session (which can be done at any point after acknowledging receipt of the initiation request, including immediately thereafter in order to decline the request), either the responder or the initiator MUST send a session-terminate action to the other party.</p>
<p>The party that terminates the session SHOULD include a <reason/> element that specifies why the session is being terminated. Examples follow.</p>
<p>Probably the primary reason for terminating a session is that the call has ended successfully; in this case, the recommended condition is <success/>.</p>
<p>Another reason for terminating the session is that the terminating party wishes to formally decline the session; in this case, the recommended condition is <decline/>.</p>
<p>Another reason for terminating the session is that the terminating party already has an existing session with the other party and wishes to use that session rather than initiate a new session; in this case, the recommended condition is <alternative-session/> and the terminating party SHOULD include the session ID of the alternative session in the <sid/> element.</p>
<p>Another reason for terminating the session is that the terminating party does not support any of the offered application formats; in this case, the recommended condition is <unsupported-applications/>.</p>
<p>Another reason for terminating the session is that the terminating party does not support any of the offered transport methods; in this case, the recommended condition is <unsupported-transports/>.</p>
<p>Note: As soon as an entity sends a session-terminate action, it MUST consider the session to be in the ENDED state (even before receiving acknowledgement from the other party). If the terminating entity receives additional Jingle-related IQ-sets from the other party after sending the session-terminate action, it MUST reply with an <unknown-session/> error.</p>
<p>Not all Jingle sessions end gracefully. When the parties to a Jingle session also exchange XMPP presence information, receipt of &UNAVAILABLE; from the other party SHOULD be considered a session-ending event that justifies proactively sending a session-terminate action to the seemingly unavailable party -- if, that is, no other communication has been received within 5 or 10 seconds from the seemingly unavailable party in the form of XMPP signalling traffic, connectivity checks, or continued media transfer.</p>
<p>At any point after initiation of a Jingle session, either entity MAY send an informational message to the other party, for example to inform the other party that a device is ringing.</p>
<p>An informational message MUST be an IQ-set containing a &JINGLE; element whose 'action' attribute is set to a value of "session-info", "description-info", or "transport-info"; the &JINGLE; element SHOULD further contain a payload child element (specific to the application format or transport method) that specifies the information being communicated. If the party that receives an informational message does not understand the payload, it MUST return a &feature; error with a Jingle-specific error condition of <unsupported-info/>.</p>
<p>However, the &JINGLE; element associated with a session-info action MAY be empty. If either party receives an empty session-info action for an active session, it MUST send an empty IQ result; this usage functions as a "ping" to determine session vitality via the XMPP signalling channel.</p>
<td>A random session identifier generated by the initiator, which effectively maps to the local-part of a SIP "Call-ID" parameter; this SHOULD match the XML Nmtoken production <note>See <<linkurl='http://www.w3.org/TR/2000/WD-xml-2e-20000814#NT-Nmtoken'>http://www.w3.org/TR/2000/WD-xml-2e-20000814#NT-Nmtoken</link>></note> so that XML character escaping is not needed for characters such as '&'.</td>
<p>The value of the 'action' attribute MUST be one of the following. If an entity receives a value not defined here, it MUST ignore the attribute and MUST return a &badrequest; error to the sender.</p>
<p>The <strong>content-add</strong> action is used to add one or more new content definitions to the session. The sender MUST specify only the added content definition(s), not the added content definition(s) plus the existing content definition(s). Therefore it is the responsibility of the recipient to maintain a local copy of the current content definition(s). If the recipient wishes to include the new content definition in the session, it MUST send a content-accept action to the other party; if not, it MUST send a content-reject action to the other party.</p>
<p>The <strong>content-modify</strong> action is used to change the direction of an existing content definition through modification of the 'senders' attribute. If the recipient deems the directionality of a content-modify action to be unacceptable, it MAY reply with a contrary content-modify action, terminate the session, or simply refuse to send or accept application data in the new direction. In any case, the recipient MUST NOT send a content-accept action in response to the content-modify.</p>
<p>The <strong>content-remove</strong> action is used to remove one or more content definitions from the session. The sender MUST specify only the removed content definition(s), not the removed content definition(s) plus the remaining content definition(s). Therefore it is the responsibility of the recipient to maintain a local copy of the current content definition(s). Upon receiving a content-remove from the other party, the recipient MUST NOT send a content-accept and MUST NOT continue to negotiate the transport method related to that content definition or send application data related to that content definition. <note>If the content-remove results in zero content definitions for the session, the entity that receives the content-remove SHOULD send a session-terminate action to the other party (since a session with no content definitions is void).</note></p>
<p>The <strong>description-info</strong> action is used to send informational hints about parameters related to the application type, such as the suggested height and width of a video display area or suggested configuration for an audio stream.</p>
<p>The <strong>session-accept</strong> action is used to definitively accept a session negotiation (implicitly this action also serves as a content-accept). A session-accept action indicates acceptance <em>only</em> of the content definition(s) whose disposition type is "session" (the default value of the &CONTENT; element's 'disposition' attribute), not any content definition(s) whose disposition type is something other than "session" (e.g., "early-session" for early media). In the session-accept stanza, the &JINGLE; element MUST contain one or more <content/> elements, each of which MUST contain one <description/> element and one <transport/> element. The &JINGLE; element SHOULD possess a 'responder' attribute that explicitly specifies the full JID of the responding entity; after sending acknowledgement of the session-accept, the initiator SHOULD send all future commmunications about this Jingle session to the JID provided in the 'responder' attribute and note the new JID in the user interface.</p>
<p>The <strong>session-info</strong> action is used to send session-level information, such as a session ping or (for Jingle RTP sessions) a ringing message.</p>
<p>The <strong>session-initiate</strong> action is used to request negotiation of a new Jingle session. When sending a session-initiate, the value of the &CONTENT; element's 'disposition' attribute MUST be "session" (to be precise, if there are multiple &CONTENT; elements then at least one MUST have a disposition of "session"); if this rule is violated, the responder MUST return a &badrequest; error to the initiator.</p>
<p>The <strong>transport-info</strong> action is used to exchange transport candidates; it is mainly used in <cite>XEP-0176</cite> but might be used in other transport specifications.</p>
<p>The <strong>transport-replace</strong> action is used to redefine a transport method, typically for fallback to a different method (e.g., changing from ICE-UDP to Raw UDP for a datagram transport, or changing from &xep0065; to &xep0047; for a streaming transport). If the recipient wishes to use the new transport definition, it MUST send a transport-accept action to the other party; if not, it MUST send a transport-reject action to the other party.</p>
<p>It is possible that two instances of certain actions can be sent at the same time in the context of an existing session, one by each party; for example, both parties might simulaneously attempt to send a content-add action. In all such cases, the action sent by the initiator MUST overrule the action sent by the responder; i.e., both parties MUST accept the action sent by the initiator and the initiator MUST return an &conflict; error to the responder for the duplicate action, which SHOULD include a Jingle-specific condition of <tie-break/>.</p>
<td>Which party originally generated the content type (used to prevent race conditions regarding modifications); the defined values are "initiator" and "responder" (where the default is "initiator").</td>
<td>How the content definition is to be interpreted by the recipient. The meaning of this attribute matches the "Content-Disposition" header as defined in &rfc2183; and applied to SIP by <cite>RFC 3261</cite>. The value of this attribute SHOULD be one of the values registered in the &ianadispositions;. The default value of this attribute is "session".</td>
<td>A unique name or identifier for the content type according to the creator, which MAY have meaning to a human user in order to differentiate this content type from other content types (e.g., two content types containing video media could differentiate between "room-pan" and "slides").</td>
<td>Which parties in the session will be generating content; the allowable values are "initiator", "responder", or "both" (where the default is "both").</td>
<li>The <reason/> element MAY contain an element qualified by some other namespace that provides more detailed machine-readable information about the reason for the action.</li>
<td>The party prefers to use an existing session with the peer rather than initiate a new session; the Jingle session ID of the alternative session SHOULD be provided as the XML character data of the <sid/> child.</td>
<p>The syntax and semantics of the <thread/> element exactly matches that of the <thread/> element for the &MESSAGE; stanza (qualified by the 'jabber:client' namespace) as defined in &xmppim;. It is used to associate a Jingle session or sessions with an ongoing conversation, so that user interfaces with the ability to present multiple interactions in the same window can show an association between the conversation and the Jingle session(s).</p>
<p>The Jingle-specific error conditions are as follows. These condition elements are qualified by the 'urn:xmpp:jingle:errors:0' namespace &VNOTE;.</p>
<td>The 'sid' attribute specifies a session that is unknown to the recipient (e.g., no longer live according to the recipient's state machine because the recipient previously terminated the session).</td>
<p>If an entity supports Jingle, it MUST advertise that fact by returning a feature of "urn:xmpp:jingle:0" &VNOTE; in response to a &xep0030; information request. The response MUST also include features for the application formats and transport methods supported by the responding entity, as described in the relevant specifications.</p>
<p>In order for an application to determine whether an entity supports this protocol, where possible it SHOULD use the dynamic, presence-based profile of service discovery defined in &xep0115;. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.</p>
<li>If and how the application format can be mapped to the Session Description Protocol, including the appropriate SDP media type (see Section 8.2.1 of <cite>RFC 4566</cite>).</li>
<li>Whether the media data for the application format shall be sent over a streaming transport method or a datagram transport method (or, if both, which is preferred).</li>
<li>Exactly how the media data is to be sent and received over a streaming or datagram transport.</li>
<p>Jingle sessions can be resource-intensive. Therefore, it is possible to launch a denial-of-service attack against an entity by burdening it with too many Jingle sessions. Care MUST be taken to accept sessions only from known entities and only if the entity's device is able to process such sessions.</p>
<p>Jingle communications can be enabled through gateways to non-XMPP networks, whose security characteristics can be quite different from those of XMPP networks. (For example, on some SIP networks authentication is optional and "from" addresses can be easily forged.) Care MUST be taken in communicating through such gateways.</p>
<p>Mere negotiation of a Jingle session can expose sensitive information about the parties (e.g., IP addresses). Care MUST be taken in communicating such information, and end-to-end encryption SHOULD be used if the parties do not trust the intermediate servers or gateways.</p>
<p>The 'initiator' and 'responder' attributes can be used to redirect a session from one JID to anther JID (i.e., the 'initiator' or 'responder' attribute might not match the 'from' or 'to' attribute of the sender). An application SHOULD NOT accept the redirection unless the bare JIDs match (i.e., the session is being redirected from one authorized resource to another authorized resource associated with the same account).</p>
<p>Upon advancement of this specification from a status of Experimental to a status of Draft, the ®ISTRAR; shall add the foregoing namespaces to the registry located at &NAMESPACES;, as described in Section 4 of &xep0053;.</p>
<p>The XMPP Registrar shall maintain a registry of Jingle application formats. All application format registrations shall be defined in separate specifications (not in this document). Application types defined within the XEP series MUST be registered with the XMPP Registrar, resulting in protocol URNs of the form "urn:xmpp:jingle:app:name:X" (where "name" is the registered name of the application format and "X" is a non-negative integer).</p>
<section2topic='Jingle Transport Methods Registry'anchor='registrar-transports'>
<p>The XMPP Registrar shall maintain a registry of Jingle transport methods. All transport method registrations shall be defined in separate specifications (not in this document). Transport methods defined within the XEP series MUST be registered with the XMPP Registrar, resulting in protocol URNs of the form "urn:xmpp:jingle:transport:name" (where "name" is the registered name of the transport method).</p>
<p>Until Jingle was developed, there existed no widely-adopted standard for initiating and managing peer-to-peer interactions between XMPP entities. Although several large service providers and Jabber client teams had written and implemented their own proprietary XMPP extensions for peer-to-peer signalling (usually only for voice), those technologies were not open and did not always take into account requirements to interoperate with SIP-based technologies. The only existing open protocol was &xep0111;, which made it possible to initiate and manage peer-to-peer sessions, but which did not provide enough of the key signalling semantics to be easily implemented in Jabber/XMPP clients. <note>It is true that TINS made it relatively easy to implement an XMPP-to-SIP gateway; however, in line with the long-time Jabber philosophy of "simple clients, complex servers", it would be better to force complexity onto the server-side gateway and to keep the client as simple as possible.</note></p>
<p>The result was an unfortunate fragmentation within the XMPP community regarding signalling protocols. Essentially, there were two possible approaches to solving the problem:</p>
<ol>
<li>Recommend that all client developers implement a dual-stack (XMPP + SIP) solution.</li>
<li>Define a full-featured protocol for XMPP signalling.</li>
<p>Implementation experience indicates that a dual-stack approach might not be feasible on all the computing platforms for which Jabber clients have been written, or even desirable on platforms where it is feasible. <note>For example, one large ISP decided to switch to a pure XMPP approach after having implemented and deployed a dual-stack client for several years.</note> Therefore, it seemed reasonable to define an XMPP signalling protocol that could provide the necessary session management semantics while also making it relatively straightforward to interoperate with existing Internet standards.</p>
<p>As a result of feedback received on <cite>XEP-0111</cite>, the original authors of this document (Joe Hildebrand and Peter Saint-Andre) began to define such a signalling protocol, code-named Jingle. Upon communication with members of the Google Talk team, <note>Google Talk is an instant messaging and voice/video chat service and client provided by Google; see <<linkurl='http://www.google.com/talk/'>http://www.google.com/talk/</link>>.</note> it was discovered that the emerging Jingle approach was conceptually (and even syntactically) quite similar to the signalling protocol used in the Google Talk application. Therefore, in the interest of interoperability and adoption, we decided to harmonize the two approaches. The signalling protocol specified herein is, therefore, substantially equivalent to the original Google Talk protocol, with several adjustments based on feedback received from implementors as well as for publication by the XMPP Standards Foundation.</p>
<p>The authors would like to thank Rohan Mahy for his valuable input on early versions of the Jingle specifications. Thiago Camargo, Diana Cionoiu, Olivier Crête, Dafydd Harries, Antti Ijäs, Tim Julien, Lauri Kaila, Justin Karneges, Jussi Laako, Steffen Larsen, Dirk Meyer, Anthony Minessale, Akito Nozaki, Matt O'Gorman, Mike Ruprecht, Rob Taylor, Matt Tucker, Justin Uberti, Saku Vainio, Brian West, Jeff Williams, and others have also provided helpful input. Thanks also to those who have commented on the &SSIG; and Jingle <note>Before this specification was formally accepted by the XMPP Standards Foundation as an XMPP Extension Protocol, it was discussed on the semi-private <jingle@jabber.org> mailing list. This list has since been resurrected as a special-purpose venue for discussion of Jingle protocols and implementation; interested developers can subscribe and access the archives at at <<linkurl='http://mail.jabber.org/mailman/listinfo/jingle/'>http://mail.jabber.org/mailman/listinfo/jingle/</link>>.</note> mailing lists.</p>
