<abstract>This specification provides a way for the initiator of a Jingle session to propose sending an invitation in an XMPP message stanza, thus taking advantage of message delivery semantics instead of sending IQ stanzas to all of the responder's online resources or choosing a particular online resource.</abstract>
<remark><p>Added explanatory text; defined more granular actions (propose, retract, accept, reject, proceed); mandated inclusion of description elements within the propose element, as in jingle-pub; defined schema.</p></remark>
<p>&xep0166; uses &IQ; stanzas for all interactions between the parties to a jingle session. When sending an invitation the initiator needs to either pick one of the responder's resources (e.g., based on &xep0115; information) or send the invitation to all of the responder's resources that support Jingle. The first method is prone to error (e.g., in cases where more than one resource supports Jingle) and the second method requires sending a separate invitation to each resource. Neither of these is ideal. Although &xep0276; proposed a way to overcome the problem, it too has issues (e.g., dependency on a presence service and the need to reveal all supported XMPP features) and in any case has not been widely implemented.</p>
<p>This document proposes an alternative solution: exchanging a &MESSAGE; stanza before sending the Jingle invitation in an &IQ; stanza. (Indeed, in the early discussions leading up to the Jingle protocol the authors considered using &MESSAGE; stanzas instead of &IQ; stanzas, but chose the latter for their deterministic handling semantics.) This method effectively results in a kind of decloaking for Jingle purposes.</p><p>&xep0280; and &xep0313; (including &xep0334;) make sure all devices (offline or not) know about the jingle session, its start timestamp and even its end timestamp and the state in between.</p>
<p>In order to prepare for sending a Jingle invitation, the initiator (e.g., Romeo) sends a &MESSAGE; stanza containing a <propose/> element qualified by the 'urn:xmpp:jingle-message:1' namespace. The <propose/> element MUST possess an 'id' attribute that will be used for the session invitation of &xep0166; and MUST contain one <description/> element for each media type associated with the intended session.</p>
<p>The server of the responder (e.g., Juliet) distributes this message stanza to all of Juliet's available resources (and to push resources as appropriate) thanks to &xep0280; and &xep0313;. Those devices might start ringing as a result.</p>
<p>Consistent with the recommendation for one-to-one chat sessions in Section 5.1 of &rfc6121;, the initiator SHOULD also send directed presence to the responder if the two entities do not already share presence information; including Entity Capabilities (XEP-0115) information in this directed presence stanza enables the responder to know the availability of the initiator (e.g., in case the message is actually delivered quite a bit later because it is saved to &xep0313; storage) and also to know the XMPP features supported by the initiator.</p>
<section2topic='Disavowing Intent to Start a Session'anchor='retract'>
<p>It can happen that the initiator might want to disavow intent to send a session invitation (e.g., because the initiator has accepted another session). The initiator can do so by sending a message stanza containing a <retract/> element specifying the same session ID.</p>
<p>The <retract/> element MUST contain a <reason/> element as defined in &xep0166; section 7.4. This SHOULD use a condition of <cancel/>, but implementations MAY use other conditions if deemed more appropriate (see <linkurl="#security">Security Considerations</link> below for details and rationale).</p>
<p>In conjunction with &xep0313; upon ending the catchup phase the responder SHOULD consider all sessions for which it received a <propose/> but no <retract/> or <finish/> message to be still active and allow the user to <linkurl="#accept">accept the intent to start a session</link>.</p>
<section2topic='Accepting Intent to Start a Session'anchor='accept'>
<p>Upon receiving the intent message, the responder's various devices will "ring" and the responder will answer the call on a particular device. Here we assume that since this is an audio-only call, Juliet chooses to take the call on the device associated with her "phone" resource.</p>
<p>Her "phone" resource informs all of her resources and all of the initiator's resources about accepting the call by sending a message to the bare JID of the initiator containing an <accept/> element specifying the session ID of the original <propose/> message.</p>
<p>Juliet's server broadcasts this accept message to all of her resources (as described in &xep0280;), which stop ringing, and to all of Romeo's resources (as described in &rfc6121;). Romeo's resources that did not send the <propose/> can use this &MESSAGE; stanza to update their UI or choose to ignore this &MESSAGE; stanza altogether.</p>
<p>Next, the device from which Juliet accepted the call sends directed presence to Romeo for the reasons described above.</p>
<p>Instead of accepting the call, the responder might want to decline the call and tell all of her devices to stop ringing (e.g., perhaps because Romeo is getting to be a bit of a nuisance). She does this by rejecting the call on one of her devices and having that device tell all of the other devices to stop ringing by sending a &MESSAGE; stanza containing a <reject/> element specifying the session ID of the original <propose/> message to the bare JID of Romeo.</p>
<p>The <reject/> element MUST contain a <reason/> element as defined in &xep0166; section 7.4. The <reason/> element SHOULD use a condition of <busy/>, but implementations MAY use other conditions if deemed more appropriate (see <linkurl="#security">Security Considerations</link> below for details and rationale).</p>
<p>In Tie-Breaking scenarios it MUST also contain a <tie-break/> element as defined in <linkurl="#tie-break-1">Tie Breaking</link>.</p>
<section2topic='Finishing a Started Session'anchor='finish'>
<p>This protocol in conjunction with &xep0280; and &xep0313; allows all devices of both involved parties to get synchronized about session start, rejection etc. To synchronize the ending of the session, both parties MUST send a message stanza containing a <finish/> element specifying the same session ID as in <linkurl='#accept'>Accept</link> to the bare jid of the other party.</p>
<p>Letting both involved parties send the <finish/> element makes sure we have the correct state in MAM archives etc. even if one client suddenly looses connectivity/power. It even makes possible for a client to determine if the call is still deemed "running" by the other party if it manages to recover from connectivity loss — before the other party runs into a timeout and sends a <finish/>— to recover the session or formally terminate the call (by ending the Jingle session and sending a <finish/> message itself). See <linkurl="#tie-break-2">Tie Breaking</link> for more infos on this and similar scenarios.</p>
<p>The <finish/> element MUST contain a <reason/> element as defined in &xep0166; section 7.4. This SHOULD use a condition of <success/>, but implementations MAY use other conditions if deemed more appropriate (see <linkurl="#security">Security Considerations</link> below for details and rationale).</p>
<p>It is possible that a <propose/> message can be sent at the same time by both parties or a new session started while one is already running. Implementations of this specification MUST implement the following solutions to solve this. (This is loosely based upon section 7.2.16 of &xep0166;.)</p>
<p>In this case (e.g. no party answered the <propose/> message yet) the lower of the two session IDs MUST overrule the other action, where by "lower" is meant the session ID that is sorted first using "i;octet" collation as specified in Section 9.3 of &rfc4790; (in the unlikely event that the random session IDs are the same, the action sent by the lower of the JabberIDs MUST overrule the other action). The party that receives the <propose/> action with the lower of the two session IDs MUST respond with an <accept/> or <reject/> mesage like it would normally do for a <propose/> message, and the party that receives the <propose/> action with the higher of the two session IDs MUST return a <reject/> message to the other party with a <tie-break/> child element alongside of a <reason/> element carrying the condition <expired/>.</p>
<examplecaption="Tie break in propose state"><