XEP-0176: Jingle ICE-UDP Transport Method

This specification defines a Jingle transport method that results in sending media data using raw datagram sockets via the User Datagram Protocol (UDP). This transport method is negotiated via the Interactive Connectivity Establishment (ICE) methodology defined by the IETF and thus provides robust NAT traversal for media traffic.

NOTICE: This document is currently within Last Call or under consideration by the XMPP Council for advancement to the next stage in the XSF standards process.

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## NOTE WELL: This Specification is provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. In no event shall the XMPP Standards Foundation or the authors of this Specification be liable for any claim, damages, or other liability, whether in an action of contract, tort, or otherwise, arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification. ##

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IPR Conformance

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Discussion Venue

Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 3920) and XMPP IM (RFC 3921) 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.

Conformance Terms

The following 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. Introduction
2. Glossary
3. Requirements
4. Jingle Conformance
5. Protocol Description
    5.1. Flow
    5.2. Transport Initiation
    5.3. Response
    5.4. Candidate Negotiation
       5.4.1. Syntax of Candidate Element
       5.4.2. Exchange of Candidates
    5.5. Connectivity Checks
    5.6. Acceptance of Successful Candidate
    5.7. Modifying an Existing Candidate
    5.8. Negotiating a New Candidate
6. Determining Support
    6.1. ICE Support
    6.2. SDP Offer / Answer Support
7. Implementation Notes
8. Deployment Notes
9. Security Considerations
    9.1. Sharing IP Addresses
    9.2. Encryption of Media
10. IANA Considerations
11. XMPP Registrar Considerations
    11.1. Protocol Namespaces
    11.2. Service Discovery Features
    11.3. Jingle Transport Methods
12. XML Schema
13. Acknowledgements
Notes
Revision History

1. Introduction

Jingle [1] 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 application formats, leaving that up to separate specifications.

The current document defines a transport method for establishing and managing data exchanges between XMPP entities over the User Datagram Protocol (see RFC 768 [2]), using the ICE methodology developed within the IETF and specified in Interactive Connectivity Establishment (ICE) [3] (hereafter referred to as ICE-CORE). Use of the ice-udp method results in a lossy transport suitable for media applications where some packet loss is tolerable (e.g., audio and video).

Note: ICE-CORE has been approved for publication as an RFC but has not yet been published as an RFC. While every effort has been made to keep this document synchronized with ICE-CORE, the interested reader is referred to ICE-CORE for a detailed description of the ICE methodology.

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

2. Glossary

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

3. Requirements

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

4. Jingle Conformance

In accordance with Section 8 of XEP-0166, this document specifies the following information related to the Jingle ice-udp transport method:

5. Protocol Description

5.1 Flow

The overall protocol flow for negotiation of the Jingle ICE-UDP Transport Method is as follows (note: many of these events happen simultaneously, not in sequence). The examples follow the scenario described in Section 17 of ICE-CORE, except that we substitute the Shakespearean characters "Romeo" and "Juliet" for the generic entities "L" and "R".

INITIATOR                     RESPONDER
    |                                    |
    |  Jingle session-initiate           |
    |----------------------------------->|
    |  Jingle ack (XMPP IQ-result)       |
    |<-----------------------------------|
    |  Jingle transport-info (candidate) |
    |----------------------------------->|
    |  Jingle ack (XMPP IQ-result)       |
    |<-----------------------------------|
    |  Jingle transport-info (candidate) |
    |----------------------------------->|
    |  Jingle ack (XMPP IQ-result)       |
    |<-----------------------------------|
    |  Jingle transport-info (candidate) |
    |<-----------------------------------|
    |  Jingle ack (XMPP IQ-result)       |
    |----------------------------------->|
    |  STUN Binding Request              |
    |    (dropped)                       |
    |  x---------------------------------|
    |  STUN Binding Request              |
    |----------------------------------->|
    |  STUN Binding Result               |
    |<-----------------------------------|
    |  STUN Binding Request              |
    |<-----------------------------------|
    |  STUN Binding Result               |
    |----------------------------------->|
    |  Jingle session-accept             |
    |<-----------------------------------|
    |  Jingle ack (XMPP IQ-result)       |
    |----------------------------------->|
    |                                    |

5.2 Transport Initiation

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. A content type MUST include one transport method. If the initiator wishes to negotiate the ice-udp transport method for an application format, it MUST include an empty <transport/> child element qualified by the 'urn:xmpp:tmp:jingle:transports:ice-udp' namespace (see Protocol Namespaces regarding issuance of one or more permanent namespaces).

Example 1. Initiation

<iq from='romeo@montague.net/orchard'
    id='jingle1'
    to='juliet@capulet.com/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:tmp:jingle'
          action='session-initiate'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <content name='this-is-the-audio-content' profile='RTP/AVP'>
      <description xmlns='urn:xmpp:tmp:jingle:apps:audio-rtp'>
        [ ... ]
      </description>
      <transport xmlns='urn:xmpp:tmp:jingle:transports:ice-udp'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'/>
    </content>
  </jingle>
</iq>

The 'pwd' and 'ufrag' attributes MUST be included in the session-initate request, in subsequent content-add and content-replace actions, and when offering candidates via the transport-info action. The attributes SHOULD NOT be included in a session-accept action. The values are separately generated for both the initiator and the responder, in accordance with ICE-CORE and as shown in the examples. The attributes are defined as follows.

Table 1: Transport Attributes

Name	Description	SDP Syntax	Example
pwd	A Password as defined in ICE-CORE.	a=ice-pwd line	asd88fgpdd777uzjYhagZg
ufrag	A User Fragment as defined in ICE-CORE.	a=ice-ufrag line	8hhy

5.3 Response

As described in XEP-0166, to acknowledge receipt of the session initiation request, the responder returns an IQ-result:

Example 2. Responder acknowledges receipt of session-initiate request

<iq from='juliet@capulet.com/balcony'
    id='jingle1'
    to='romeo@montague.net/orchard'
    type='result'/>

5.4 Candidate Negotiation

Once the responder acknowledges receipt of 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. [7]

Note: In order to expedite session establishment, the initiator MAY send transport candidates immediately after sending the "session-initiate" message and before receiving acknowledgement from the responder (i.e., the initiator MUST consider the session to be live even before receiving acknowledgement). Given in-order delivery, the responder should receive such "transport-info" messages after receiving the "session-initiate" message; if not, it is appropriate for the responder to return <unknown-session/> errors since according to its state machine the session does not exist. If either party receives an <unknown-session/> from the other party, it MUST terminate the negotiation and the session.

Note: See the Security Considerations section of this document regarding the exposure of IP addresses on behalf by the responder's client.

The candidate syntax and negotiation flow are described below.

5.4.1 Syntax of Candidate Element

The following is an example of the candidate format:

Example 3. A candidate transport

<candidate component='1'
           foundation='1'
           generation='0'
           ip='10.0.1.1'
           network='0'
           port='8998'
           priority='2130706431'
           protocol='udp'
           type='host'/>

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

Table 2: Candidate Attributes

Name	Description	SDP Syntax	Example
component	A Component ID as defined in ICE-CORE.	Component ID value in a=candidate line	1
foundation	A Foundation as defined in ICE-CORE.	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	192.0.2.3
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).	N/A	0
port	The port at the candidate IP address.	Port value in a=candidate line	45664
priority	A Priority as defined in ICE-CORE [8]	Priority value in a=candidate line	2130706431
protocol	The protocol to be used. The only allowable value is "udp".	Transport protocol field in a=candidate line	udp
rel-addr	A related address as defined in ICE-CORE.	raddr value in a=candidate line	10.0.1.1
rel-port	A related port as defined in ICE-CORE.	rport value in a=candidate line	8998
rem-addr	A IP address for a remote address as defined in ICE-CORE.	connection-address value in a=remote-candidates line	192.0.2.1
rem-port	The port for a remote address as defined in ICE-CORE.	port value in a=remote-candidates line	3478
type	A Candidate Type as defined in ICE-CORE. The allowable values are "host" for host candidates, "prflx" for peer reflexive candidates, "relay" for relayed candidates, and "srflx" for server reflexive candidates.	Typ field in a=candidate line	srflx

5.4.2 Exchange of Candidates

The first step in negotiating connectivity is for each party to immediately begin sending transport candidates to the other party. [9] These candidates SHOULD be gathered by following the procedure specified in Section 4.1.1 of ICE-CORE (typically by communicating with a stanadlone STUN server in order to discover the client's public IP address and port) and prioritized by following the procedure specified in Section 4.1.2 of ICE-CORE.

Each candidate or set of candidates shall be sent as <candidate/> children of a <transport/> element qualified by the 'urn:xmpp:tmp:jingle:transports:ice-udp' namespace. The <transport/> element shall be sent via a Jingle action of "transport-info" as shown in the examples below.

Either party MAY include multiple <candidate/> elements in one <transport/> element. Sending one candidate per transport-info action typically results in a faster negotiation because the candidates most likely to succeed are sent first and it is not necessary to gather all candidates before beginning to send any candidates. Furthermore, because certain candidates may be more "expensive" in terms of bandwidth or processing power, the initiator may not want to advertise their existence unless it is necessary to do so after other candidates have failed.) However, sending multiple candidates in a single "transport-info" action can help to ensure interoperability with entities that implement the SDP offer/answer model described in RFC 3264. An entity SHOULD send one candidate per "transport-info" action and send multiple such actions, instead of sending multiple candidates in a single "transport-info" action; the only exception is if the other party advertises support for the "urn:ietf:rfc:3264" service discovery feature.

If the responder receives and can successfully process a given candidate or set of candidates, it returns an IQ-result (if not, for example because the candidate data is improperly formatted, it returns an error). Note: The responder is only indicating receipt of the candidate or set of candidates, not telling the initiator that the candidate will be used.

The initiator keeps sending candidates (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. For each candidate or set of candidates, the responder acknowledges receipt.

At the same time (i.e., immediately after acknowledging receipt of the session-initiate request, not waiting for the initiator to begin or finish sending candidates), the responder also begins sending potential candidates, in order of desirability according to the responder. As above, the initiator acknowledges receipt of the candidates.

Example 4. Initiator sends some candidates

<iq from='romeo@montague.net/orchard'
    id='info1'
    to='juliet@capulet.com/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:tmp:jingle'
          action='transport-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <transport xmlns='urn:xmpp:tmp:jingle:transports:ice-udp'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'>
        <candidate component='1'
                   foundation='1'
                   generation='0'
                   ip='10.0.1.1'
                   network='1'
                   port='8998'
                   priority='2130706431'
                   protocol='udp'
                   type='host'/>
      </transport>
    </content>
  </jingle>
</iq>

<iq from='romeo@montague.net/orchard'
    id='info2'
    to='juliet@capulet.com/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:tmp:jingle'
          action='transport-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <transport xmlns='urn:xmpp:tmp:jingle:transports:ice-udp'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'>
        <candidate component='1'
                   foundation='2'
                   generation='0'
                   ip='192.0.2.3'
                   network='1'
                   port='45664'
                   priority='1694498815'
                   protocol='udp'
                   rel-addr='10.0.1.1'
                   rel-port='8998'
                   type='srflx'/>
      </transport>
    </content>
  </jingle>
</iq>

For each candidate received, the other party (in this case the responder) MUST acknowledge receipt or return an error.

Example 5. Responder acknowledges receipt

<iq from='juliet@capulet.com/balcony'
    id='info1'
    to='romeo@montague.net/orchard'
    type='result'/>

<iq from='juliet@capulet.com/balcony'
    id='info2'
    to='romeo@montague.net/orchard'
    type='result'/>

At the same time (i.e., immediately after acknowledging the session-initation request, not waiting for the initiator to begin or finish sending candidates), the responder also sends candidates that may work for it.

Example 6. Responder sends candidates

<iq from='juliet@capulet.lit/balcony'
    to='romeo@montague.lit/orchard'
    id='info3'
    type='set'>
  <jingle xmlns='urn:xmpp:tmp:jingle'
          action='transport-info'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <transport xmlns='urn:xmpp:tmp:jingle:transports:ice-udp'
                 pwd='YH75Fviy6338Vbrhrlp8Yh'
                 ufrag='9uB6'>
        <candidate component='1'
                   foundation='1'
                   generation='0'
                   ip='192.0.2.1'
                   network='0'
                   port='3478'
                   priority='2130706431'
                   protocol='udp'
                   type='host'/>
      </transport>
    </content>
  </jingle>
</iq>

As above for the candidates sent by the responder, here the initiator acknowledges receipt of the candidates sent by the responder.

Example 7. Initiator acknowledges receipt

<iq from='romeo@montague.lit/orchard'
    id='info3'
    to='juliet@capulet.lit/balcony'
    type='result'/>

5.5 Connectivity Checks

As the initiator and responder receive candidates, they probe the various candidate transports for connectivity. In performing these connectivity checks, each party SHOULD follow the procedure specified in Section 7 of ICE-CORE. The following business rules apply:

Each party sends a STUN Binding Request (see draft-ietf-behave-rfc3489bis [10]) from each local candidate it generated to each remote candidate it received.
In accordance with ICE-CORE, the STUN Binding Request MUST include the PRIORITY attribute (computed according to Section 7.1.1.1. of ICE-CORE).
For the purposes of the Jingle ICE-UDP Transport Method, both parties are full ICE implementations and therefore the controlling role MUST be assumed by the initiator and the controlled role MUST be assumed by the responder.
The STUN Binding Requests generated by the initiator MAY include the USE-CANDIDATE attribute to indicate that the initiator wishes to cease checks for this component.
The STUN Binding Requests generated by the initiator MUST include the ICE-CONTROLLING attribute.
The STUN Binding Requests generated by the responder MUST include the ICE-CONTROLLED attribute.
The parties MUST use STUN short term credentials to authenticate requests and perform message integrity checks. As in ICE-CORE, the username in the STUN Binding Request is of the form "ufrag-of-sender:ufrag-of-peer" and the password is the value of the 'pwd' attribute provided by the peer. [11]

When it receives a STUN Binding Request, each party MUST return a STUN Binding Response, which may indicate either an error case or the success case. As described in Section 7.1.2.2 of ICE-CORE, a connectivity check succeeds if the STUN transaction generated a success response, the source IP address and port of the response equals the destination IP address and port that the Binding Request was sent to, and the destination IP address and port of the response match the source IP address and port that the Binding Request was sent from.

For the candidates exchanged in the previous section, the connectivity checks would be as follows. In particular, the parties send one STUN Binding Request from each of their local candidates to each of the remote candidates.

INITIATOR                  NAT                  RESPONDER
    |                       |                       |
    |                       | STUN Binding Request  |
    |                       | from 192.0.2.1:3478   |
    |                       | to   10.0.1.1:8998    |
    |                       |   (dropped)           |
    |                       |  x--------------------|
    | STUN Binding Request  |                       |
    | from 10.0.1.1:8998    |                       |
    | to   192.0.2.1:3478   |                       |
    | USE-CANDIDATE         |                       |
    |---------------------->|                       |
    |                       | STUN Binding Request  |
    |                       | from 192.0.2.3:45664  |
    |                       | to   192.0.2.1:3478   |
    |                       | USE-CANDIDATE         |
    |                       |---------------------->|
    |                       | STUN Binding Response |
    |                       | from 192.0.2.1:3478   |
    |                       | to   192.0.2.3:45664  |
    |                       |<----------------------|
    | STUN Binding Response |                       |
    | from 192.0.2.1:3478   |                       |
    | to   10.0.1.1:8998    |                       |
    | map  192.0.2.3:45664  |                       |
    |<----------------------|                       |
    |================RTP now can flow==============>|
    |                       | STUN Binding Request  |
    |                       | from 192.0.2.1:3478   |
    |                       | to   192.0.2.3:45664  |
    |                       |<----------------------|
    | STUN Binding Request  |                       |
    | from 192.0.2.1:3478   |                       |
    | to   10.0.1.1:8998    |                       |
    |<----------------------|                       |
    | STUN Binding Response |                       |
    | from 10.0.1.1:8998    |                       |
    | to   192.0.2.1:3478   |                       |
    | map  192.0.2.1:3478   |                       |
    |---------------------->|                       |
    |                       | STUN Binding Response |
    |                       | from 192.0.2.3:45664  |
    |                       | to   192.0.2.1:3478   |
    |                       | map  192.0.2.1:3478   |
    |                       |---------------------->|
    |<===============RTP now can flow===============|
    |                       |                       |

Note: Here the initiator (controlling agent) is using "aggressive nomination" as described in Section 8.1.1.2 of ICE-CORE and therefore includes the USE-CANDIDATE attribute in the STUN Binding Requests it sends.

5.6 Acceptance of Successful Candidate

If, based on STUN connectivity checks, the parties determine that they will be able to exchange media between a given pair of local candidates and remote candidates (i.e., the pair is "nominated" and ICE processing is "completed"), the parties shall proceed as follows:

The responder sends a Jingle session-accept action to the initiator.
The initiator acknowledges receipt of the session-accept.

First, the responder sends a session-accept action to the initiator, specifying the candidate that succeeded. The session-accept MUST contain information about the nominated pair, including the "rem-addr" and "rem-port" attributes (which specify the IP address and port for the responder's end of the pair, which is a "remote address" according to the initiator). This enables both parties to explicitly agree to both ends of the connection pair (i.e., the local address+port and the remote address+port).

Example 8. Responder definitively accepts the successful candidate

<iq from='juliet@capulet.com/balcony'
    id='accept1'
    to='romeo@montague.net/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:tmp:jingle'
          action='session-accept'
          initiator='romeo@montague.net/orchard'
          responder='juliet@capulet.com/balcony'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <description xmlns='urn:xmpp:tmp:jingle:apps:audio-rtp'>
        [ ... ]
      </description>
      <transport xmlns='urn:xmpp:tmp:jingle:transports:ice-udp'>
        <candidate component='1'
                   foundation='1'
                   generation='0'
                   ip='192.0.2.3'
                   network='1'
                   port='45664'
                   priority='1694498815'
                   protocol='udp'
                   rel-addr='10.0.1.1'
                   rel-port='8998'
                   rem-addr='192.0.2.1'
                   rem-port='3478'
                   type='srflx'/>
      </transport>
    </content>
  </jingle>
</iq>

The <jingle/> element in the session-accept stanza SHOULD possess a 'responder' attribute that explicitly specifies the full JID of the responding entity. If the 'responder' attribute is provided, all future commmunications SHOULD be sent to the JID provided in the 'responder' attribute.

Since according to the connectivity checks the initiator can also send data over that candidate, it acknowledges the responder's acceptance:

Example 9. Initiator acknowledges acceptance of successful candidate

<iq from='romeo@montague.net/orchard'
    id='accept1'
    to='juliet@capulet.com/balcony'
    type='result'/>

Now the initiator and responder can begin sending data over the negotiated connection (in fact, they could have sent data as soon as the connectivity checks succeeded, as shown in the preceding examples).

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

Example 10. Initiator returns error in response to acceptance of successful candidate

<iq from='romeo@montague.net/orchard'
    id='accept1'
    to='juliet@capulet.com/balcony'
    type='error'>
  <error type='cancel'>
    <not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</iq>

If the responder cannot find a suitable candidate transport or it receives a <not-acceptable/> error from the initiator in response to its acceptance of a suitable transport, it SHOULD terminate the session as described in Section 6.8 of XEP-0166.

5.7 Modifying an Existing Candidate

The creator of a content type MAY modify an existing, in-use candidate at any time during the session, for example to change the IP address or port. This is done by sending a content-replace action with the changed candidate information, where the value of the 'generation' is incremented to specify that the candidate information is a modification to an existing candidate.

An example follows (change to IP address and port).

Example 11. Initiator modifies the in-use candidate

<iq from='romeo@montague.net/orchard'
    id='rep2'
    to='juliet@capulet.com/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:tmp:jingle'
          action='content-replace'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <transport xmlns='urn:xmpp:tmp:jingle:transports:ice-udp'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'>
        <candidate component='1'
                   foundation='1'
                   generation='1'
                   ip='192.0.2.3'
                   network='1'
                   port='45665'
                   priority='1694498815'
                   protocol='udp'
                   type='srflx'/>
      </transport>
    </content>
  </jingle>
</iq>

The recipient then acknowledges receipt.

Example 12. Recipient acknowledges content-replace

<iq from='juliet@capulet.com/balcony'
    id='rep2'
    to='romeo@montague.net/orchard'
    type='result'/>

If the content-replace is acceptable, the recipient then sends a content-accept action.

Example 13. Responder definitively accepts the replaced candidate

<iq from='juliet@capulet.com/balcony'
    id='accept2'
    to='romeo@montague.net/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:tmp:jingle'
          action='content-accept'
          initiator='romeo@montague.net/orchard'
          responder='juliet@capulet.com/balcony'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <description xmlns='urn:xmpp:tmp:jingle:apps:audio-rtp'>
        [ ... ]
      </description>
      <transport xmlns='urn:xmpp:tmp:jingle:transports:ice-udp'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'>
        <candidate component='1'
                   foundation='1'
                   generation='1'
                   ip='192.0.2.3'
                   network='1'
                   port='45665'
                   priority='1694498815'
                   protocol='udp'
                   type='srflx'/>
      </transport>
    </content>
  </jingle>
</iq>

The initiator then acknowledges the responder's acceptance:

Example 14. Initiator acknowledges content acceptance

<iq from='romeo@montague.net/orchard'
    id='accept2'
    to='juliet@capulet.com/balcony'
    type='result'/>

The parties then use the modified candidate in subsequent communications.

5.8 Negotiating a New Candidate

Even after content acceptance or session acceptance, either party MAY continue to send additional candidates to the other party (e.g., because the user agent has become aware of a new media proxy or NIC). As above, such candidates are shared by sending a transport-info action.

Example 15. Initiator sends a fourth candidate

<iq from='romeo@montague.net/orchard'
    id='info4'
    to='juliet@capulet.com/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:tmp:jingle'
          action='transport-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <transport xmlns='urn:xmpp:tmp:jingle:transports:ice-udp'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'>
        <candidate component='1'
                   foundation='1'
                   generation='0'
                   ip='10.0.1.2'
                   network='0'
                   port='9001'
                   priority='21149780477'
                   protocol='udp'
                   type='host'/<
      </transport>
    </content>
  </jingle>
</iq>

The receiving party MUST acknowledge receipt of the candidate.

Example 16. Recipient acknowledges receipt

<iq from='juliet@capulet.com/balcony'
    id='info4'
    to='romeo@montague.net/orchard'
    type='result'/>

The parties SHOULD check the newly-offered candidate for connectivity, as described previously. If the parties determine that media can flow over the candidate, the initiating party shall send a content-replace action to the responder.

Example 17. Initiator sends content-replace

<iq from='romeo@montague.net/orchard'
    id='rep3'
    to='juliet@capulet.com/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:tmp:jingle'
          action='content-replace'
          initiator='romeo@montague.net/orchard'
          responder='juliet@capulet.com/balcony'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content'>
      <description xmlns='urn:xmpp:tmp:jingle:apps:audio-rtp' profile='RTP/AVP'>
        [ ... ]
      </description>
      <transport xmlns='urn:xmpp:tmp:jingle:transports:ice-udp'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'>
        <candidate component='1'
                   foundation='1'
                   generation='0'
                   ip='10.0.1.2'
                   network='0'
                   port='9001'
                   priority='21149780477'
                   protocol='udp'
                   type='host'/>
      </transport>
    </content>
  </jingle>
</iq>

The responder then acknowledges the replaced content definition.

Example 18. Responder acknowledges content-replace

<iq from='juliet@capulet.com/balcony'
    id='rep3'
    to='romeo@montague.net/orchard'
    type='result'/>

The responder then accepts the replaced content definition.

Example 19. Responder definitively accepts the replaced content definition

<iq from='juliet@capulet.com/balcony'
    id='accept3'
    to='romeo@montague.net/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:tmp:jingle'
          action='content-accept'
          initiator='romeo@montague.net/orchard'
          responder='juliet@capulet.com/balcony'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <description xmlns='urn:xmpp:tmp:jingle:apps:audio-rtp'>
        [ ... ]
      </description>
      <transport xmlns='urn:xmpp:tmp:jingle:transports:ice-udp'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'>
        <candidate component='1'
                   foundation='1'
                   generation='0'
                   ip='10.0.1.2'
                   network='0'
                   port='9001'
                   priority='21149780477'
                   protocol='udp'
                   type='host'/>
      </transport>
    </content>
  </jingle>
</iq>

The initiator then acknowledges content acceptance.

Example 20. Initiator acknowledges content acceptance

<iq from='romeo@montague.net/orchard'
    id='accept3'
    to='juliet@capulet.com/balcony'
    type='result'/>

The parties then use the new candidate in subsequent communications.

6. Determining Support

6.1 ICE Support

If an entity supports the Jingle ice-udp transport, it MUST return a feature of "urn:xmpp:tmp:jingle:transports:ice-udp" (see Protocol Namespaces regarding issuance of one or more permanent namespaces) in response to Service Discovery [12] information requests.

Example 21. Service discovery information request

<iq from='romeo@montague.net/orchard'
    id='disco1'
    to='juliet@capulet.com/balcony'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>

Example 22. Service discovery information response

<iq from='juliet@capulet.com/balcony'
    id='disco1'
    to='romeo@montague.net/orchard'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    ...
    <feature var='urn:xmpp:tmp:jingle:transports:ice-udp'/>
    ...
  </query>
</iq>

Naturally, support MAY also be determined via the dynamic, presence-based profile of Service Discovery defined in Entity Capabilities [13].

6.2 SDP Offer / Answer Support

If an entity supports the SDP offer / answer model described in RFC 3264 and therefore prefers to receive multiple candidates in a single "transport-info" action, it MUST advertise support for the "urn:ietf:rfc:3264" service discovery feature. Typically this feature will be advertised only by gateways between Jingle and SIP.

Example 23. Service discovery information request

<iq from='romeo@montague.net/orchard'
    id='disco2'
    to='sip.shakespeare.lit'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>

Example 24. Service discovery information response

<iq from='sip.shakespeare.lit'
    id='disco2'
    to='romeo@montague.net/orchard'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    ...
    <feature var='urn:ietf:rfc:3264'/>
    <feature var='urn:xmpp:tmp:jingle:transports:ice-udp'/>
    ...
  </query>
</iq>

7. Implementation Notes

In order to speed the negotiation process so that media can flow as quickly as possible, the initiatior should gather and prioritize candidates in advance, or as soon as the principal begins the process of initiating a session.

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).

8. Deployment Notes

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. See External Service Discovery [14] for related information.

9. Security Considerations

9.1 Sharing IP Addresses

By definition, the exchange of transport candidates results in exposure of the sender's IP addresses, which comprise a form of personally identifying information. A Jingle client MUST enable a user to control which entities will be allowed to receive such information. If a human user explicitly accepts a session request, then the client should consider that action to imply approval of IP address sharing. However, waiting for a human user to explicitly accept the session request can result in delays during session setup, since it is more efficient to immediately begin sharing transport candidates. Therefore, it is RECOMMENDED for the client to immediately send transport candidates to a contact (without waiting for explicit user approval of the session request) in the following cases:

The user has permanently and formally authorized the contact to view the user's presence information via a presence subscription as reflected in an XMPP roster item (see XMPP IM [15]).
The user has temporarily and dynamically shared presence with the contact via "directed presence" as described in RFC 3921.
The user has explicitly added the contact to a "whitelist" of entities who may access the user's personally-identifying information.

9.2 Encryption of Media

In order to secure the data stream that is negotiated via the Jingle ICE transport, implementations SHOULD use encryption methods appropriate to the transport method and media being exchanged (for details regarding RTP exchanges, refer to Jingle RTP Sessions [16]).

10. IANA Considerations

11. XMPP Registrar Considerations

11.1 Protocol Namespaces

Until this specification advances to a status of Draft, its associated namespaces shall be:

urn:xmpp:tmp:jingle:transports:ice-udp

Upon advancement of this specification, the XMPP Registrar [18] shall issue permanent namespaces in accordance with the process defined in Section 4 of XMPP Registrar Function [19].

The following namespaces are requested, and are thought to be unique per the XMPP Registrar's requirements:

urn:xmpp:jingle:transport:ice-udp

11.2 Service Discovery Features

If an entity supports the SDP offer / answer model described in RFC 3264 and therefore prefers to receive one "transport-info" action with multiple candidates, it MUST advertise support for the "urn:ietf:rfc:3264" feature.

The registry submission is as follows.

Registry Submission

<var>
  <name>urn:ietf:rfc:3264</name>
  <desc>Signals support for the SDP offer / answer model described in RFC 3264</desc>
  <doc>XEP-0176</doc>
</var>

11.3 Jingle Transport Methods

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

<transport>
  <name>ice-udp</name>
  <desc>
    A method for negotiation of out-of-band UDP connections with built-in NAT
    and firewall traversal, equivalent to the IETF's Interactive Connectivity
    Establishment (ICE) methodology when resulting in the use of UDP as the
    transport protocol.
  </desc>
  <type>lossy</type>
  <doc>XEP-0176</doc>
</transport>

12. XML Schema

<?xml version='1.0' encoding='UTF-8'?>

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='urn:xmpp:tmp:jingle:transports:ice-udp'
    xmlns='urn:xmpp:tmp:jingle:transports:ice-udp'
    elementFormDefault='qualified'>

  <xs:element name='transport'>
    <xs:complexType>
      <xs:sequence>
        <xs:element ref='candidate' minOccurs='0' maxOccurs='unbounded'/>
      </xs:sequence>
      <xs:attribute name='pwd' type='xs:string' use='optional'/>
      <xs:attribute name='ufrag' type='xs:string' use='optional'/>
    </xs:complexType>
  </xs:element>

  <xs:element name='candidate'>
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base='empty'>
          <xs:attribute name='component' type='xs:unsignedByte' use='required'/>
          <xs:attribute name='foundation' type='xs:unsignedByte' use='required'/>
          <xs:attribute name='generation' type='xs:unsignedByte' use='required'/>
          <xs:attribute name='ip' type='xs:string' use='required'/>
          <xs:attribute name='network' type='xs:unsignedByte' use='required'/>
          <xs:attribute name='port' type='xs:unsignedShort' use='required'/>
          <xs:attribute name='priority' type='xs:positiveInteger' use='required'/>
          <xs:attribute name='protocol' type='xs:NCName' use='required'/>
          <xs:attribute name='rel-addr' type='xs:string' use='optional'/>
          <xs:attribute name='rel-port' type='xs:unsignedShort' use='optional'/>
          <xs:attribute name='rem-addr' type='xs:string' use='optional'/>
          <xs:attribute name='rem-port' type='xs:unsignedShort' use='optional'/>
          <xs:attribute name='type' use='required'>
            <xs:simpleType>
              <xs:restriction base='xs:NCName'>
                <xs:enumeration value='host'/>
                <xs:enumeration value='prflx'/>
                <xs:enumeration value='relay'/>
                <xs:enumeration value='srflx'/>
              </xs:restriction>
            </xs:simpleType>
          </xs:attribute>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>

  <xs:simpleType name='empty'>
    <xs:restriction base='xs:string'>
      <xs:enumeration value=''/>
    </xs:restriction>
  </xs:simpleType>

</xs:schema>

13. Acknowledgements

Thanks to Diana Cionoiu, Olivier Crête, Tim Julien, Steffen Larsen, Robert McQueen, Mike Ruprecht, and Paul Witty for their feedback.

Notes

1. XEP-0166: Jingle <http://www.xmpp.org/extensions/xep-0166.html>.

2. RFC 768: User Datagram Protocol <http://tools.ietf.org/html/rfc0768>.

3. Interactive Connectivity Establishment (ICE): A Methodology for Network Address Translator (NAT) Traversal for Offer/Answer Protocols <http://tools.ietf.org/html/draft-ietf-mmusic-ice>. Work in progress.

4. RFC 3264: An Offer/Answer Model with the Session Description Protocol (SDP) <http://tools.ietf.org/html/rfc3264>.

5. RFC 4566: SDP: Session Description Protocol <http://tools.ietf.org/html/rfc4566>.

6. RFC 3550: RTP: A Transport Protocol for Real-Time Applications <http://tools.ietf.org/html/rfc3550>.

7. 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 other specifications, such as XEP-0166. This document specifies only negotiation of the ICE transport method.

8. In accordance with the rules specified in Section 4.1.1 of ICE-CORE, the priority values shown in the examples within this document have been calculated as follows. The "type preference" for host candidates is stipulated to be "126" and for server reflexive candidates "100". The "local preference" for network 0 is stipulated to be "4096", for network 1 "2048", and for network 2 "1024".

9. The fact that both parties send candidates means that Jingle requires each party to be a full implementation of ICE, not a lite implementation as specified in ICE-CORE.

10. Session Traversal Utilities for NAT (STUN) <http://tools.ietf.org/html/draft-ietf-behave-rfc3489bis>.

11. Thus when Romeo sends a STUN Binding Request to Juliet the credentials will be STUN username "8hhy:9uB6" and password "YH75Fviy6338Vbrhrlp8Yh" whereas when Juliet sends a STUN Binding Request to Romeo the credentials will be STUN username "9uB6:8hhy" and password "asd88fgpdd777uzjYhagZg".

12. XEP-0030: Service Discovery <http://www.xmpp.org/extensions/xep-0030.html>.

13. XEP-0115: Entity Capabilities <http://www.xmpp.org/extensions/xep-0115.html>.

14. XEP-0215: External Service Discovery <http://www.xmpp.org/extensions/xep-0215.html>.

15. RFC 3921: Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence <http://tools.ietf.org/html/rfc3921>.

16. XEP-0167: Jingle RTP Sessions <http://www.xmpp.org/extensions/xep-0167.html>.

17. 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/>.

18. 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 <http://www.xmpp.org/registrar/>.

19. XEP-0053: XMPP Registrar Function <http://www.xmpp.org/extensions/xep-0053.html>.

Revision History

Version 0.19 (2008-06-04)

Allowed batching of multiple candidates in a single transport-info action for optional interworking with the SDP offer-answer model, and added urn:ietf:rfc:3264 service discovery feature to advertise such support; updated security considerations regarding sharing of IP addresses.

(psa)

Version 0.18 (2008-05-28)

Removed content-replace action from acceptance flow, since in ICE that information is sent via STUN, not in the signalling channel.

(psa)

Version 0.17 (2008-03-20)

Moved pwd and ufrag attributes from candidate element to transport element since they describe session-level or media-level information.

(psa)

Version 0.16 (2008-02-29)

Changed content-modify to content-replace per XEP-0166.

(psa)

Version 0.15 (2008-01-06)

Clarified several small points regarding candidate gathering procedures and STUN connectivity checks.

(psa)

Version 0.14 (2008-01-02)

Modified flow for ICE completion to require content-modify from initiator to responder, thus mapping to sending of revised offer in SIP; added rem-addr and rem-port attributes to map to a=remote-candidates information in SDP; changed raddr and rport attributes to rel-addr and rel-port to prevent confusion with rem-addr and rem-port attributes.

(psa)

Version 0.13 (2007-12-28)

Added further details about connectivity checks; defined raddr and rport attributes for complete mapping to SDP.

(psa)

Version 0.12 (2007-11-28)

Moved ice-tcp definition to a separate specification.

(psa)

Version 0.11 (2007-11-27)

Further editorial review; also added sections on modification of existing candidates and exchange of subsequent candidates.

(psa)

Version 0.10 (2007-11-15)

Editorial review and consistency check.

(psa)

Version 0.9 (2007-06-28)

Updated to track ICE-16.

(psa)

Version 0.8 (2007-04-17)

Separately defined ice-tcp and ice-udp transport methods to enable clearer definition of transport methods and reuse by application types; specified Jingle conformance, including definition of ice-udp as lossy and ice-tcp as reliable.

(psa)

Version 0.7 (2007-03-23)

Updated to track ICE-14 and ICE-TCP-03; moved text on discovery of STUN servers to separate specification.

(psa)

Version 0.6 (2006-12-21)

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

(psa)

Version 0.5 (2006-10-31)

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

(psa)

Version 0.4 (2006-09-13)

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

(psa)

Version 0.3 (2006-07-12)

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

(se/psa)

Version 0.2 (2006-03-24)

Recommended use of RTP-native methods for DTMF.

(psa)

Version 0.1 (2006-03-01)

Initial version (split from XEP-0166).

(psa/jb)

XEP-0176: Jingle ICE-UDP Transport Method

Document Information

Author Information

Joe Beda

Scott Ludwig

Peter Saint-Andre

Joe Hildebrand

Sean Egan

Legal Notices

Copyright

Permissions

Disclaimer of Warranty

Limitation of Liability

IPR Conformance

Discussion Venue

Relation to XMPP

Conformance Terms

Table of Contents

1. Introduction

2. Glossary

3. Requirements

4. Jingle Conformance

5. Protocol Description

5.1 Flow

5.2 Transport Initiation

5.3 Response

5.4 Candidate Negotiation

5.4.1 Syntax of Candidate Element

5.4.2 Exchange of Candidates

5.5 Connectivity Checks

5.6 Acceptance of Successful Candidate

5.7 Modifying an Existing Candidate

5.8 Negotiating a New Candidate

6. Determining Support

6.1 ICE Support

6.2 SDP Offer / Answer Support

7. Implementation Notes

8. Deployment Notes

9. Security Considerations

9.1 Sharing IP Addresses

9.2 Encryption of Media

10. IANA Considerations

11. XMPP Registrar Considerations

11.1 Protocol Namespaces

11.2 Service Discovery Features

11.3 Jingle Transport Methods

12. XML Schema

13. Acknowledgements

Notes

Revision History

Version 0.19 (2008-06-04)

Version 0.18 (2008-05-28)

Version 0.17 (2008-03-20)

Version 0.16 (2008-02-29)

Version 0.15 (2008-01-06)

Version 0.14 (2008-01-02)

Version 0.13 (2007-12-28)

Version 0.12 (2007-11-28)

Version 0.11 (2007-11-27)

Version 0.10 (2007-11-15)

Version 0.9 (2007-06-28)

Version 0.8 (2007-04-17)

Version 0.7 (2007-03-23)

Version 0.6 (2006-12-21)

Version 0.5 (2006-10-31)

Version 0.4 (2006-09-13)

Version 0.3 (2006-07-12)

Version 0.2 (2006-03-24)

Version 0.1 (2006-03-01)