Because Jingle (XEP-0166)  uses <iq/> stanzas for all interactions between the parties to a session, when sending an invitation the initiator needs to either pick one of the responder's resources (e.g., based on Entity Capabilities (XEP-0115)  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 Presence Decloaking (XEP-0276)  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.
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.
This protocol was designed with the following requirements in mind:
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:0' namespace. The <propose/> element MUST possess an 'id' attribute that will be used for the session invitation and MUST contain one <description/> element for each media type associated with the intended session.
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). Those devices might start ringing as a result.
Consistent with the recommendation for one-to-one chat sessions in Section 5.1 of RFC 6121 , 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 offline storage) and also to know the XMPP feautures supported by the initiator.
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.
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.
As a first step, her "phone" resource informs all of her resources about accepting the call by sending a message to her own bare JID containing an <accept/> element specifying the session ID of the original <propose/> message.
Juliet's server broadcasts this accept message to all of her available resources (as described in RFC 6121), which stop ringing:
Next, the device from which Juliet accepted the call tells Romeo to proceed with the session (via a message stanza containing a <proceed/> element), and also sends directed presence for the reasons described above.
Instead of accepting the call, the responder might want to ignore 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, in the form of a message to her own bare JID containing an <reject/> element specifying the session ID of the original <propose/> message.
Juliet's server broadcasts this reject message to all of her available resources (as described in RFC 6121), which stop ringing:
Next, the responder MAY want to decline the call explicitly, in the form of a message to the sender’s full JID containing a <reject/> element specifying the session ID of the original <propose/> message.
Now Romeo actually initiates the session (segue to Jingle itself).
The following issues remain to be closed:
Thanks to Lance Stout for his feedback.
Because exchanging messages with other entities is effectively is a presence leak, an XMPP client that implements the receiving side of this specification MUST disable sending of proceed messages by default and MUST enable the feature only as a result of explicit user confirmation. Such confirmation can be provided per request, by whitelisting requests received from Jingle initiators in the responder's contact list, or through some other suitable means as long as sending proceed messages does not occur by default.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) .
This specification defines the following XML namespace:
If the protocol defined in this specification undergoes a revision that is not fully backwards-compatible with an older version, the XMPP Registrar shall increment the protocol version number found at the end of the XML namespaces defined herein, as described in Section 4 of XEP-0053.
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Add explicit reject by responding to sender with reject message.
Initial published version approved by the XMPP Council.
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.