XEP-0177: Jingle Raw UDP Transport

This document defines a Jingle transport method that results in sending data over a raw User Datagram Protocol (UDP) connection.

WARNING: This Standards-Track document is Experimental. Publication as an XMPP Extension Protocol does not imply approval of this proposal by the XMPP Standards Foundation. Implementation of the protocol described herein is encouraged in exploratory implementations, but production systems should not deploy implementations of this protocol until it advances to a status of Draft.

Document Information

Series: XEP
Number: 0177
Publisher: XMPP Standards Foundation
Status: Experimental
Type: Standards Track
Version: 0.7
Last Updated: 2007-06-25
Approving Body: XMPP Council
Dependencies: XMPP Core, XEP-0166
Supersedes: None
Superseded By: None
Short Name: TO BE ASSIGNED
Wiki Page: <http://wiki.jabber.org/index.php/Jingle Raw UDP Transport (XEP-0177)>

Author Information

Joe Beda

Email: jbeda@google.com
JabberID: jbeda@google.com

Peter Saint-Andre

Email: stpeter@jabber.org
JabberID: stpeter@jabber.org

Scott Ludwig

Email: scottlu@google.com
JabberID: scottlu@google.com

Joe Hildebrand

Email: jhildebrand@jabber.com
JabberID: hildjj@jabber.org

Sean Egan

Email: seanegan@google.com
JabberID: seanegan@google.com

Legal Notice

This XMPP Extension Protocol is copyright 1999 - 2007 by the XMPP Standards Foundation (XSF) and is in full conformance with the XSF's Intellectual Property Rights Policy <http://www.xmpp.org/extensions/ipr-policy.shtml>. This material may be distributed only subject to the terms and conditions set forth in the Creative Commons Attribution License (<http://creativecommons.org/licenses/by/2.5/>).

Discussion Venue

The preferred venue for discussion of this document is the Standards discussion list: <http://mail.jabber.org/mailman/listinfo/standards>.

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".

Table of Contents


1. Introduction
2. Requirements
3. Jingle Conformance
4. Protocol Description
    4.1. Transport Initiation
    4.2. Responder Response
       4.2.1. Sending Media
       4.2.2. Sending A Candidate
       4.2.3. Sending An Informational Message
    4.3. Informational Messages
5. Determining Support
6. Security Considerations
7. IANA Considerations
8. XMPP Registrar Considerations
    8.1. Protocol Namespaces
    8.2. Jingle Transport Methods
9. XML Schema
    9.1. Transport
    9.2. Informational Messages
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 content formats, leaving that up to separate specifications. The current document defines a transport method for establishing and managing data between XMPP entities using a raw User Datagram Protocol (UDP) connection (see RFC 768 [2]). This "raw-udp" method results in a lossy transport method suitable for use in media applications where some packet loss is tolerable (e.g., audio and video).

2. Requirements

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 over the IP address and port that the parties consider most likely to succeed.
  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.

Note: The Raw UDP transport does not provide traversal of Network Address Translators (NATs); if NAT traversal is needed, Jingle ICE Transport Method [3] SHOULD be used. The Raw UDP transport method is defined only for the purpose of specifying the IP address and port that an entity considers "most likely to succeed" and is a "hit-or-miss" method that may work in some circumstances. The method can therefore be thought of as the Jingle equivalent of the "I'm Feeling Lucky" button; it is also helpful for use in unit-testing of Jingle implementation by developers working on a local network (see Bootstrapping Implementation of Jingle [4]).

3. Jingle Conformance

In accordance with Section 8 of XEP-0166, this document specifies the following information related to the Jingle Raw UDP transport type:

  1. The transport negotiation process is defined in the Protocol Description section of this document.

  2. The semantics of the <description/> element are defined in the Transport Initiation section of this document.

  3. Successful negotiation of the Raw UDP method results in use of a lossy transport that is suitable for applications where some packet loss is tolerable, such as audio and video.

  4. If multiple components are to be communicated over the transport, the first component shall be associated with the port in the transport initiation stanza and the second component (e.g., for RTCP) shall be associated with a UDP port that is one number higher than the specified port (e.g., if the specified port is 13540 then the port for the second component shall be 13541).

4. Protocol Description

4.1 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. This stanza MUST include at least one content type. If the initiator wishes to negotiate the Raw UDP transport for a given content type, it MUST include a <transport/> child element qualified by the 'http://www.xmpp.org/extensions/xep-0177.html#ns' namespace (see Protocol Namespaces), which MUST [5] include the initiator's Raw UDP candidate via the 'ip', 'port', 'generation', and 'name' attributes of the <candidate/> element.

Example 1. Initiation Example

<iq from='romeo@montague.net/orchard' to='juliet@capulet.com/balcony' id='jingle1' type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-initiate'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content'>
      <description ...>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0177.html#ns'>
        <candidate ip='10.1.1.104' port='13540' generation='0'/>
      </transport>
    </content>
  </jingle>
</iq>

The 'generation', 'ip', and 'port' attributes are REQUIRED. The 'ip' and 'port' attributes are self-explanatory. The 'generation' attribute provides a tracking mechanism for determining which version of this candidate is in force (this is useful if the candidate is redefined mid-stream, for example if the port is changed).

Note: The "Raw UDP candidate" is the candidate that the entity has reason to believe will be most likely to succeed for that content type, and thus is equivalent to the "default" candidate as described in Section 4.1.3 of Interactive Connectivity Establishment (ICE) [6]. This is not necessarily the entity's preferred address for communication, but instead is the "address most likely to succeed", i.e., the address that is assumed to be reachable by the vast majority of target entities. To determine reachability, the client needs classify ahead of time the permissiveness of the NAT or firewall it is behind, if any. It then SHOULD assign the Raw UDP candidate as follows, where the candidate types are as described in ICE:

Table 1: Raw UDP Candidate Assignment

NAT Type Recommended Raw UDP Candidate Type
None Host candidate
Symmetric (not permissive) Relay candidate
Permissive Server reflexive or peer reflexive candidate discovered via RFC 3489 [7]

4.2 Responder Response

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

Example 2. Responder Provisionally Accepts the Session Request

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

Once the responder provisionally accepts the session, it:

These are done simultaneously in order to ensure that a connection can be made, since the initiator's Raw UDP candidate may not result in success.

4.2.1 Sending Media

The responder MUST immediately attempt to send data to the IP and port specified in the initiation request. If all goes well, the data will be received by the initiator and media will flow. Because delivery of UDP data is not acknowledged, a party that receives media SHOULD send an informational message of <received/> to the other party as specified below.

4.2.2 Sending A Candidate

As noted, the responder SHOULD send its own Raw UDP candidate to the initiator by sending a transport-info message to the initiator, as shown in the following example.

Example 3. Responder Sends Its Raw UDP Candidate

<iq from='juliet@capulet.com/balcony' to='romeo@montague.net/orchard' id='jingle2' type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='transport-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content'>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0177.html#ns'>
        <candidate ip='208.245.212.67' port='9876' generation='0'/>
      </transport>
    </content>
  </jingle>
</iq>

The initiator MUST then acknowledge receipt by returning an IQ result (or a standard XMPP error).

Example 4. Initiator Acknowledges Receipt of Candidate

<iq from='romeo@montague.net/orchard' to='juliet@capulet.com/balcony' type='result' id='jingle2'/>

Naturally, the initiator SHOULD also attend to send media to the responder as specified above. This media too may or may not get through, but if it does then the other party should acknowledge receipt.

4.2.3 Sending An Informational Message

When it attempts to send data to a Raw UDP candidate, a party SHOULD send an informational message of <trying/>. If a party receives data, it SHOULD send an informational message of <received/>.

Each informational message MUST be an IQ-set containing a <jingle/> element of type "session-info", where the informational message is a payload element specified in the Informational Messages section of this document.

4.3 Informational Messages

Informational messages MAY be sent by the either party within the context of the Raw UDP transport to communicate whether the party has attempted to send media or has received media. The informational message MUST be an IQ-set containing a <jingle/> element of type "session-info", where the informational message is a payload element qualified by the 'http://www.xmpp.org/extensions/xep-0177.html#ns-info' namespace (see Protocol Namespaces regarding issuance of one or more permanent namespaces). The following payload elements are defined:

Table 2: Information Payload Elements

Element Meaning
<received/> The party has received media.
<trying/> The party is trying to send media.

Note: Because the informational message is sent in an IQ-set, the receiving party MUST return either an IQ-result or an IQ-error (normally only an IQ-result to acknowledge receipt; no error flows are defined or envisioned at this time).

5. Determining Support

If an entity supports the Jingle Raw UDP transport, it MUST return a feature of "http://www.xmpp.org/extensions/xep-0177.html#ns" (see Protocol Namespaces regarding issuance of one or more permanent namespaces) in response to Service Discovery [8] information requests.

Example 5. Service Discovery information request

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

Example 6. Service Discovery information response

<iq type='result'
    from='juliet@capulet.com/balcony'
    to='romeo@montague.net/orchard'
    id='disco1'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    ...
    <feature var='http://www.xmpp.org/extensions/xep-0177.html#ns'/>
    ...
  </query>
</iq>

6. Security Considerations

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 audio and video exchanges via RTP, refer to XEP-0167 and XEP-0180).

7. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [9].

8. XMPP Registrar Considerations

8.1 Protocol Namespaces

Until this specification advances to a status of Draft, its associated namespaces shall be "http://www.xmpp.org/extensions/xep-0177.html#ns" and "http://www.xmpp.org/extensions/xep-0177.html#ns-info"; upon advancement of this specification, the XMPP Registrar [10] shall issue permanent namespaces in accordance with the process defined in Section 4 of XMPP Registrar Function [11].

8.2 Jingle Transport Methods

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

<transport>
  <name>raw-udp</name>
  <desc>A method for exchanging data over a raw UDP connection.</desc>
  <type>lossy</type>
  <doc>XEP-0176</doc>
</transport>

9. XML Schema

9.1 Transport

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='http://www.xmpp.org/extensions/xep-0177.html#ns'
    xmlns='http://www.xmpp.org/extensions/xep-0177.html#ns'
    elementFormDefault='qualified'>

  <xs:element name='transport'>
    <xs:complexType>
      <xs:sequence>
        <xs:element ref='candidate' minOccurs='0' maxOccurs='1'/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

  <xs:element name='candidate'>
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base='empty'>
          <xs:attribute name='generation' type='xs:unsignedByte' use='required'/>
          <xs:attribute name='ip' type='xs:string' use='required'/>
          <xs:attribute name='port' type='xs:unsignedShort' use='required'/>
        </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>

9.2 Informational Messages

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='http://www.xmpp.org/extensions/xep-0177.html#ns-info'
    xmlns='http://www.xmpp.org/extensions/xep-0177.html#ns-info'
    elementFormDefault='qualified'>

  <xs:element name='received' type='empty'/>

  <xs:element name='trying' type='empty'/>

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

</xs:schema>

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. XEP-0176: Jingle ICE Transport Method <http://www.xmpp.org/extensions/xep-0176.html>.

4. XEP-0208: Bootstrapping Implementation of Jingle <http://www.xmpp.org/extensions/xep-0208.html>.

5. This is required to avoid a round trip and help expedite the negotiation.

6. 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.

7. RFC 3489: STUN - Simple Traversal of User Datagram Protocol (UDP) Through Network Address Translators (NATs) <http://tools.ietf.org/html/rfc3489>.

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

9. 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/>.

10. 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/>.

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

Revision History

Version 0.7 (2007-06-25)

More clearly specified the hit-or-miss nature of the transport; corrected informational messages.

(psa)

Version 0.6 (2007-04-17)

Specified Jingle conformance, including definition of transport type as lossy; added section on service discovery.

(psa)

Version 0.5 (2007-03-23)

Updated to reflect changes to XEP-0166; clarified media data checking.

(psa)

Version 0.4 (2006-12-21)

Recommended sending of candidate in initiation request to save a round trip and expedite the negotiation; removed name attribute; clarified flow of negotiation; modified spec to use provisional namespace before advancement to Draft (per XEP-0053).

(psa)

Version 0.3 (2006-10-31)

Added informational messages; clarified connectivity checks and acceptance process; mentioned that the Raw UDP candidate is conceptually equivalent to the concept of an in-use candidate from the ICE specification; added reference to RFC 4347.

(psa)

Version 0.2 (2006-07-12)

Removed candidate element and specified exchange of address information via transport-info messages; clarified usage of name attribute.

(se/psa)

Version 0.1 (2006-03-01)

Initial version (split from XEP-0166).

(psa/jb)

END