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Jingle ICE Transport This document defines a Jingle transport method that results in sending data between two entities using the Interactive Connectivity Establishment (ICE) methodology. &LEGALNOTICE; 0176 Experimental Standards Track Standards Council XMPP Core XEP-0166 TO BE ASSIGNED &stpeter; &joebeda; &scottlu; &hildjj; &seanegan; 0.6 2006-12-21 psa

Modified spec to use provisional namespace before advancement to Draft (per XEP-0053).

 0.5 2006-10-31 psa

Updated to track ICE-12; corrected service discovery process; completed editorial review; removed mention of DTMF, which is for audio only.

 0.4 2006-09-13 psa

Updated to track ICE-10; added section on service discovery.

 0.3 2006-07-12 se/psa

Specified that DTMF must use in-band signalling (XEP-0181).

 0.2 2006-03-24 psa

Recommended use of RTP-native methods for DTMF.

 0.1 2006-03-01 psa/jb

Initial version (split from XEP-0166).

Note: This document depends on the IETF's &ice; specification, which is a work in progress. Every effort has been made to keep this document synchronized with draft-ietf-mmusic-ice, for which the latest published version is 13 (hereafter referred to as "&icecurr;"). The interested reader is referred to the &icecurr; for a detailed description of the ICE methodology, which for the most part this document merely maps to XMPP syntax.

&xep0166; defines a framework for negotiating and managing out-of-band data sessions over XMPP. In order to provide a flexible framework, the base Jingle specification defines neither data transport methods nor content formats, leaving that up to separate specifications. The current document defines a transport method for establishing and managing data connections between XMPP entities, using the ICE methodology currently being developed within the IETF.

The process for ICE negotiation is largely the same in Jingle as it is in &icecurr;. There are several differences:

The Jingle transport method defined herein is designed to meet the following requirements:

  1. Make it possible to establish and manage out-of-band connections between two XMPP entities, even if they are behind Network Address Translators (NATs) or firewalls.
  2. Make it relatively easy to implement support in standard Jabber/XMPP clients.
  3. 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.

The reader is referred to &icecurr; for a description of various terms used in the context of ICE. Those terms are not reproduced here.

In order for the initiator in a Jingle exchange to start the negotiation, it MUST send a Jingle "session-initiate" stanza as described in XEP-0166. This stanza MUST include at least one transport method. If the initiator wishes to negotiate the ICE transport, it MUST include an empty &TRANSPORT; child element qualified by the 'http://www.xmpp.org/extensions/xep-0176.html#ns' namespace (see Protocol Namespaces).

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As described in XEP-0166, to provisionally accept the session initiation request, the responder returns an IQ-result:

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If the responder provisionally accepts the session initiation request as shown above, both initiator and responder MUST immediately negotiate connectivity over the ICE transport by exchanging XML-formatted candidate transports for the channel. This negotiation proceeds immediately in order to maximize the possibility that media can be exchanged as quickly as possible. Concurrent with negotiation of the ICE candidates, it is possible for the initiator and responder to negotiate which content types the session will include, which transport methods will be tried for each content type, etc. Those negotiation flows are shown in XEP-0166. This document specifies only negotiation of the ICE transport method.

The candidate syntax and negotiation flow are described below.

The following is an example of the candidate format:

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The attributes of the <candidate/> element are described in the following table:

Name Description SDP Syntax Example
component A Component ID as defined in &icecurr; Component ID value in a=candidate line 1
foundation A Foundation as defined in &icecurr; Foundation value in a=candidate line 1
generation An index, starting at 0, that enables the parties to keep track of updates to the candidate throughout the life of the session N/A 0
ip The Internet Protocol (IP) address for the candidate transport mechanism; this may be either an IPv4 address or an IPv6 address IP Address value in a=candidate line 10.0.1.1
network An index, starting at 0, referencing which network this candidate is on for a given peer (used for diagnostic purposes if the calling hardware has more than one Network Interface Card or NIC) N/A 0
port The port at the candidate IP address Port value in a=candidate line 8998
priority A Priority as defined in &icecurr; In accordance with the rules specified in Section 5.2 of &icecurr;, the priority values shown in the examples within this document have been calculated as follows. The "type preference" for local candidates is stipulated to be "126" and for server reflexive candidates "66". The "local preference" for network 0 is stipulated to be "4096", for network 1 "2048", and for network 2 "1024". Priority value in a=candidate line 9909
protocol The protocol to be used; allowable values are: "udp" (when standard &icecurr; is used); "tcp", "tcp-act", and "tcp-pass" (when &ice-tcp; is used); and "ssltcp" (definition to follow) Transport protocol field in a=candidate line udp
pwd A Password as defined in &icecurr; a=ice-pwd line asd88fgpdd777uzjYhagZg
type A Candidate Type as defined in &icecurr;; the allowable values are "host" for host candidates, "srflx" for server reflexive candidates, "prflx" for peer reflexive candidates, and "relay" for relayed candidates Typ field in a=candidate line srflx
ufrag A User Fragment as defined in &icecurr; a=ice-ufrag line 8hhy

The first step in negotiating connectivity is for each client to immediately begin sending candidate transport methods to the other client. These candidates SHOULD be gathered by following the procedure specified in Section 5.1 of &icecurr; and prioritized by following the procedure specified in Section 5.2 of &icecurr;. Each candidate MUST be sent in a &JINGLE; element with an action of "transport-info".

If the responder receives and can successfully process a given candidate, it returns an IQ-result (if not, for example because the candidate data is improperly formatted, it returns an error).

Note well that the responder is only indicating receipt of the candidate, not telling the initiator that the candidate will be used.

The initiator keeps sending candidates, one after the other (without stopping to receive an acknowledgement of receipt from the responder for each candidate) until it has exhausted its supply of possible or desirable candidate transports. (Because certain candidates may be more "expensive" in terms of bandwidth or processing power, the initiator may not want to advertise their existence unless necessary.) For each candidate, the responder acknowledges receipt.

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, client SHOULD follow the procedure specified in Section 7 of &icecurr;.

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For each candidate received, the other party MUST acknowledge receipt or return an error:

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If, based on STUN connectivity checks, the responder determines that it will be able to establish a connection using a given candidate, it sends a &JINGLE; element with an action of 'transport-accept' to the initiator, specifying the candidate that succeeded:

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The &JINGLE; element in the transport-accept stanza SHOULD possess a 'responder' attribute that explicitly specifies the full JID of the responding entity. If provided, all future commmunications SHOULD be sent to the JID provided in the 'responder' attribute.

If the initiator can also send data over that candidate, then it acknowledges the responder's acceptance:

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Now the initiator and responder can begin sending data over the negotiated connection.

If a candidate succeeded for the responder but the initiator cannot send data over that candidate, it MUST return a ¬acceptable; error in response to the responder's acceptance of the successful candidate:

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If the responder cannot find a suitable candidate transport or it receives a ¬acceptable; error from the initiator in response to its acceptance of a suitable transport, it SHOULD terminate the session as described in Section 5.9 of XEP-0166.

If an entity supports this specification, it MUST return a feature of "http://www.xmpp.org/extensions/xep-0176.html#ns" in response to &xep0030; information requests.

As mentioned in the Deployment Notes of this document, the administrator of an XMPP server may wish to deploy a STUN server in order to ease the process of negotiating use of the Jingle ICE transport. A client can become aware of a STUN server in the following ways:

  1. Specified in the default settings for the client (while this may seem sub-optimal, it is acceptable at present because there are so few public STUN servers).
  2. Manually added by a human user into the client's configuration.
  3. Discovered via DNS SRV records as specified in Section 9.1 of &rfc3489;.
  4. Discovered via the XMPP &xep0030; extension.

It is OPTIONAL for a STUN server to support XMPP for the purpose of service discovery. Therefore, client developers SHOULD NOT depend on the existence of XMPP-aware STUN servers.

If a STUN server is accessible via XMPP, it SHOULD be advertised by returning an appropriate item in response to service discovery item requests sent to the address of an XMPP server:

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A subsequent service discovery information request to the STUN server MUST result in a response indicating that the STUN server has a service discovery category of "proxy" and type of "stun", as well as advertisement of appropriate service discovery features (because the XMPP interaction is necessary only in order to discover the identity of the STUN server, the only feature that an XMPP-aware STUN server SHOULD advertise is "http://jabber.org/protocol/disco#info".)

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This specification applies exclusively to Jabber/XMPP clients and places no additional requirements on Jabber/XMPP servers. However, service administrators may wish to deploy a STUN server in order to ease the client-to-client negotiation process.

In order to secure the end-to-end data stream, implementations SHOULD use encryption methods appropriate to the transport method in use.

This document requires no interaction with &IANA;.

Until this specification advances to a status of Draft, its associated namespace shall be "http://www.xmpp.org/extensions/xep-0176.html#ns"; upon advancement of this specification, the ®ISTRAR; shall issue a permanent namespace in accordance with the process defined in Section 4 of &xep0053;.

The XMPP Registrar shall include "ice" in its registry of Jingle transport methods. The registry submission is as follows:

ice A method for negotiation of out-of-band connections with built-in NAT and firewall traversal, equivalent to the IETF's Interactive Connectivity Establishment (ICE) methodology. XEP-0176 ]]>

The XMPP Registrar shall include a Service Discovery type of "stun" within the "proxy" category.

The registry submission is as follows:

proxy stun a STUN (Simple Traversal of UDP through NATs) service per RFC 3489 XEP-0176 ]]> ]]>