The Jingle (XEP-0166) [1] extensions to XMPP provide a technology for setup, management, and teardown of multimedia sessions between two entities, with an initial focus on voice over Internet Protocol (VoIP). By design, Jingle has been kept relatively simple and it does not cover the kind of advanced features that are available on the public switched telephone network (PSTN) and traditional private branch exchange (PBX) systems. However, because Jingle and XMPP itself provide an extensible technology for the real-time exchange of XML data, more advanced use cases can be defined through additional extensions. This document specifies one such extension, for the transfer of a session from one entity to another entity using either attended transfer or unattended transfer (for the difference between these scenarios, see for example RFC 5359 [2]). Although this extension will likely be used mainly in the context of VoIP interactions, it could also be used for any Jingle application type, such as video chat or screen sharing.
The session flow for negotiating an unattended transfer is as follows:
Caller Attendant Callee | | | | session-initiate | | |----------------------->| | | ack | | |<-----------------------| | | session-accept | | |<-----------------------| | | ack | | |----------------------->| | | transfer | | |<-----------------------| | | ack | | |----------------------->| | | hold | | |----------------------->| | | ack | | |<-----------------------| | | session-initiate | |------------------------------------------------>| | ack | |<------------------------------------------------| | terminate | | |----------------------->| | | ack | | |<-----------------------| | | session-accept | |<------------------------------------------------| | ack | |------------------------------------------------>| | AUDIO (RTP) | |<===============================================>| | |
The protocol flow is shown below, where the caller is "caller@example.net", the attendant is "attendant@office.example.com", and the callee is "boss@execs.example.com".
First the caller initiates a normal call to the attendant.
<iq from='caller@example.net/phone'
id='i3hd81k8'
to='attendant@office.example.com/desk'
type='set'>
<jingle xmlns='urn:xmpp:jingle:1'
action='session-initiate'
initiator='caller@example.net/phone'
sid='851ba2'>
<content creator='initiator'
disposition='session'
name='urgent-communication'>
<description xmlns='urn:xmpp:jingle:apps:rtp:1'
media='audio'>
<payload-type id='0' name='PCMU' />
</description>
<transport xmlns='urn:xmpp:jingle:transports:ice-udp:1'>
...
</transport>
</content>
</jingle>
</iq>
The attendant's phone then acknowledges the session request.
<iq from='attendant@office.example.com/desk'
id='i3hd81k8'
to='caller@example.net/phone'
type='result'/>
Next the attendant answers the call.
<iq from='attendant@office.example.com/desk'
id='k1d26dcv'
to='caller@example.net/phone'
type='set'>
<jingle xmlns='urn:xmpp:jingle:1'
action='session-accept'
initiator='caller@example.net/phone'
responder='attendant@office.example.com/desk'
sid='851ba2'>
<content creator='initiator'
disposition='session'
name='urgent-communication'>
<description xmlns='urn:xmpp:jingle:apps:rtp:1'
media='audio'>
<payload-type id='0' name='PCMU' />
</description>
<transport xmlns='urn:xmpp:jingle:transports:ice-udp:1'>
...
</transport>
</jingle>
</iq>
The caller acknowledges the session-accept.
<iq from='caller@example.net/phone'
id='k1d26dcv'
to='attendant@office.example.com/desk'
type='result'/>
Now the attendant decides to transfer the call. It does this by sending a Jingle action of type session-info to the caller, specifying the address of the callee via a <transfer/> element qualified by the "urn:xmpp:jingle:transfer:0" namespace (see Namespace Versioning regarding the possibility of incrementing the version number).
<iq from='attendant@office.example.com/desk'
id='a0pl3v76'
to='caller@example.net/phone'
type='set'>
<jingle xmlns='urn:xmpp:jingle:1'
action='session-info'
initiator='caller@example.net/phone'
responder='attendant@office.example.com/desk'
sid='851ba2'>
<transfer xmlns='urn:xmpp:jingle:transfer:0'
to='boss@execs.example.com/phone'/>
</jingle>
</iq>
If the caller understands the transfer request, it acknowledges the request (if not, it MUST return a <feature-not-implemented/> error as specified in XEP-0166).
<iq from='attendant@office.example.com/desk'
to='caller@example.net/phone'
id='a0pl3v76'
type='result'/>
Now the caller puts the attendant on hold.
<iq from='attendant@office.example.com/desk'
id='o4bd91v4'
to='caller@example.net/phone'
type='set'>
<jingle xmlns='urn:xmpp:jingle:1'
action='session-info'
initiator='caller@example.net/phone'
sid='851ba2'>
<hold xmlns='urn:xmpp:jingle:apps:rtp:info:1'/>
</jingle>
</iq>
While the attendant is on hold, the caller initiates a new call to the callee. The session-initiation request includes a <transfer/> element that specifies the attendant's address.
<iq from='caller@example.net/phone'
id='r7y2nxv3'
to='boss@execs.example.com/phone'
type='set'>
<jingle xmlns='urn:xmpp:jingle:1'
action='session-initiate'
initiator='caller@example.net/phone'
sid='1a332d'>
<content creator='initiator'
disposition='session'
name='urgent-communication'>
<description xmlns='urn:xmpp:jingle:apps:rtp:1'
media='audio'>
<payload-type id='0' name='PCMU' />
</description>
<transport xmlns='urn:xmpp:jingle:transports:ice-udp:1'>
...
</transport>
</content>
<transfer xmlns='urn:xmpp:jingle:transfer:0'
from='attendant@office.example.com/desk'/>
</jingle>
</iq>
The callee acknowledges the call.
<iq from='boss@execs.example.com/phone'
to='caller@example.net/phone'
id='r7y2nxv3'
type='result'/>
Now the caller's phone detects the successful transfer, so it hangs up on the attendant:
<iq from='caller@example.net/phone'
id='hg34cx20'
to='attendant@office.example.com/desk'
type='set'>
<jingle xmlns='urn:xmpp:jingle:1'
action='session-terminate'
initiator='attendant@office.example.com/desk'
sid='851ba2'>
<reason>
<success/>
<transferred xmlns='urn:xmpp:jingle:transfer:0'/>
<text>Unattended transfer success</text>
</reason>
</jingle>
</iq>
The session flow for negotiating an attended transfer is as follows:
Caller Attendant Callee | | | | session-initiate | | |----------------------->| | | ack | | |<-----------------------| | | session-accept | | |<-----------------------| | | ack | | |----------------------->| | | | session-initiate | | |----------------------->| | | ack | | |<-----------------------| | transfer | | |<-----------------------| | | ack | | |----------------------->| | | hold | | |----------------------->| | | ack | | |<-----------------------| | | session-initiate | |------------------------------------------------>| | ack | |<------------------------------------------------| | terminate | | |----------------------->| | | ack | | |<-----------------------| | | session-accept | |<------------------------------------------------| | ack | |------------------------------------------------>| | AUDIO (RTP) | |<===============================================>| | |
The protocol flow is shown below, where the caller is "caller@example.net", the attendant is "attendant@office.example.com", and the callee is "boss@execs.example.com".
First the caller initiates a normal call to the attendant.
<iq from='caller@example.net/phone'
id='m4hs861b'
to='attendant@office.example.com/desk'
type='set'>
<jingle xmlns='urn:xmpp:jingle:1'
action='session-initiate'
initiator='caller@example.net/phone'
sid='851ba2'>
<content creator='initiator'
disposition='session'
name='urgent-communication'>
<description xmlns='urn:xmpp:jingle:apps:rtp:1'
media='audio'>
<payload-type id='0' name='PCMU' />
</description>
<transport xmlns='urn:xmpp:jingle:transports:ice-udp:1'>
...
</transport>
</content>
</jingle>
</iq>
The attendant's phone then acknowledges the session request.
<iq from='attendant@office.example.com/desk'
to='caller@example.net/phone'
id='m4hs861b'
type='result'/>
Next the attendant answers the call.
<iq from='attendant@office.example.com/desk'
to='caller@example.net/phone'
id='u72bx793'
type='set'>
<jingle xmlns='urn:xmpp:jingle:1'
action='session-accept'
initiator='caller@example.net/phone'
responder='attendant@office.example.com/desk'
sid='851ba2'>
<content creator='initiator'
disposition='session'
name='urgent-communication'>
<description xmlns='urn:xmpp:jingle:apps:rtp:1'
media='audio'>
<payload-type id='0' name='PCMU' />
</description>
<transport xmlns='urn:xmpp:jingle:transports:ice-udp:1'>
...
</transport>
</jingle>
</iq>
The caller acknowledges the session-accept.
<iq from='caller@example.net/phone'
id='u72bx793'
to='attendant@office.example.com/desk'
type='result'/>
Next the attendant makes a call to the callee for the purpose of completing an attended transfer. Before doing so, the attendant SHOULD verify that the callee supports Jingle session transfer, as described under Determining Support.
<iq from='attendant@office.example.com/desk'
id='t57caw2r'
to='boss@execs.example.com/phone'
type='set'>
<jingle xmlns='urn:xmpp:jingle:1'
action='session-initiate'
initiator='attendant@office.example.com/desk'
sid='663e9f'>
<content creator='initiator'
disposition='session'
name='urgent-communication'>
<description xmlns='urn:xmpp:jingle:apps:rtp:1'
media='audio'>
<payload-type id='0' name='PCMU' />
</description>
<transport xmlns='urn:xmpp:jingle:transports:ice-udp:1'>
...
</transport>
</content>
</jingle>
</iq>
The callee acknowledges the session-initiate.
<iq from='boss@execs.example.com/phone'
id='t57caw2r'
to='attendant@office.example.com/desk'
type='result'/>
Now the attendant transfers the call by sending a session-info action to the caller containing details about the attendant's session with the callee.
<iq from='attendant@office.example.com/desk'
id='p4hslk49'
to='caller@example.net/phone'
type='set'>
<jingle xmlns='urn:xmpp:jingle:1'
action='session-info'
initiator='caller@example.net/phone'
responder='attendant@office.example.com/desk'
sid='851ba2'>
<transfer xmlns='urn:xmpp:jingle:transfer:0'
from='attendant@office.example.com/desk'
sid='663e9f'
to='boss@execs.example.com/phone'/>
</jingle>
</iq>
If the caller understands the transfer request, it acknowledges the request (if not, it MUST return a <feature-not-implemented/> error as specified in XEP-0166).
<iq from='attendant@office.example.com/desk'
id='p4hslk49'
to='caller@example.net/phone'
type='result'/>
Now the caller puts the attendant on hold.
<iq from='attendant@office.example.com/desk'
id='o4bd91v4'
to='caller@example.net/phone'
type='set'>
<jingle xmlns='urn:xmpp:jingle:1'
action='session-info'
initiator='caller@example.net/phone'
sid='851ba2'>
<hold xmlns='urn:xmpp:jingle:apps:rtp:info:1'/>
</jingle>
</iq>
While the attendant is on hold, the caller initiates a new call to the callee. The session-initiation request includes a <transfer/> element that specifies the attendant's address and the SessionID of the attendant's session with the callee.
<iq from='caller@example.net/phone'
id='w93b461v'
to='boss@execs.example.com/phone'
type='set'>
<jingle xmlns='urn:xmpp:jingle:1'
action='session-initiate'
initiator='caller@example.net/phone'
sid='851ba2'>
<content creator='initiator'
disposition='session'
name='urgent-communication'>
<description xmlns='urn:xmpp:jingle:apps:rtp:1'
media='audio'>
<payload-type id='0' name='PCMU' />
</description>
<transport xmlns='urn:xmpp:jingle:transports:ice-udp:1'>
...
</transport>
</content>
<transfer xmlns='urn:xmpp:jingle:transfer:0'
from='attendant@office.example.com/desk'
sid='663e9f'
to='boss@execs.example.com/phone'/>
</jingle>
</iq>
The callee identifies an active session with the same from+to+sid and replaces that with the incoming call, so it hangs up on the existing session with the attendant.
<iq from='boss@execs.example.com/phone'
id='yh2f36s5'
to='attendant@office.example.com/desk'
type='set'>
<jingle xmlns='urn:xmpp:jingle:1'
action='session-terminate'
initiator='attendant@office.example.com/desk'
sid='663e9f'>
<reason>
<success/>
<transferred xmlns='urn:xmpp:jingle:transfer:0'/>
<text>Attended transfer success</text>
</reason>
</jingle>
</iq>
The callee then acknowledges the session request from the caller.
<iq from='boss@execs.example.com/phone'
to='caller@example.net/phone'
id='w93b461v'
type='result'/>
Now the caller's phone detects the successful transfer, so it hangs up on the attendant:
<iq from='caller@example.net/phone'
id='yh2f36s5'
to='attendant@office.example.com/desk'
type='set'>
<jingle xmlns='urn:xmpp:jingle:1'
action='session-terminate'
initiator='attendant@office.example.com/desk'
sid='851ba2'>
<reason>
<success/>
<transferred xmlns='urn:xmpp:jingle:transfer:0'/>
<text>Unattended transfer success</text>
</reason>
</jingle>
</iq>
If an entity supports session transfers, it MUST advertise that fact by returning a feature of "urn:xmpp:jingle:transfer:0" (see Namespace Versioning regarding the possibility of incrementing the version number) in response to Service Discovery (XEP-0030) [3] information requests.
<iq from='caller@example.net/phone
id='u891vad3'
to='attendant@office.example.com/desk'
type='get'>
<query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
<iq from='attendant@office.example.com/desk'
id='u891vad3'
to='caller@example.net/phone
type='result'>
<query xmlns='http://jabber.org/protocol/disco#info'>
<feature var='urn:xmpp:jingle:1'/>
<feature var='urn:xmpp:jingle:transfer:0'/>
</query>
</iq>
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 Entity Capabilities (XEP-0115) [4]. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.
In unattended transfer, the callee has no way to verify that the attendant specified in the session-initiate request received from the caller was actually involved in the transaction. This implies that:
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [5].
This specification defines the following XML namespace:
Upon advancement of this specification from a status of Experimental to a status of Draft, the XMPP Registrar [6] shall add the foregoing namespaces to the registry located at <https://xmpp.org/registrar/namespaces.html>, as described in Section 4 of XMPP Registrar Function (XEP-0053) [7].
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.
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:xmpp:jingle:transfer:0'
xmlns='urn:xmpp:jingle:transfer:0'
elementFormDefault='qualified'>
<xs:element name='transfer'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='empty'>
<xs:attribute name='from' type='xs:string' use='optional'/>
<xs:attribute name='sid' type='xs:string' use='optional'/>
<xs:attribute name='to' type='xs:string' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='transferred' type='empty'/>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
Thanks to Robert McQueen for his feedback.
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The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.
The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.
Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.
Errata can be sent to <editor@xmpp.org>.
The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
1. XEP-0166: Jingle <https://xmpp.org/extensions/xep-0166.html>.
2. RFC 5359: Session Initiation Protocol Service Examples <http://tools.ietf.org/html/rfc5359>.
3. XEP-0030: Service Discovery <https://xmpp.org/extensions/xep-0030.html>.
4. XEP-0115: Entity Capabilities <https://xmpp.org/extensions/xep-0115.html>.
5. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.
6. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.
7. XEP-0053: XMPP Registrar Function <https://xmpp.org/extensions/xep-0053.html>.
Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/
Updated examples; added reference to RFC 5359; added security considerations regarding unattended transfer.
Initial published version.
Added XML schema.
First draft.
END