JEP-0111: A Transport for Initiating and Negotiating Sessions (TINS)

This JEP defines a SIP-compatible transport for initiating and negotiating sessions using SDP over XMPP.

WARNING: This Standards-Track JEP is Experimental. Publication as a Jabber Enhancement Proposal does not imply approval of this proposal by the Jabber Software 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.

JEP Information

Status: Experimental
Type: Standards Track
Number: 0111
Version: 0.7
Last Updated: 2005-05-12
JIG: Standards JIG
Approving Body: Jabber Council
Dependencies: XMPP Core, RFC 2327, RFC 3261
Supersedes: None
Superseded By: None
Short Name: tins
Wiki Page: <http://wiki.jabber.org/index.php/A Transport for Initiating and Negotiating Sessions (TINS) (JEP-0111)>

Author Information

Legal Notice

This Jabber Enhancement Proposal is copyright 1999 - 2005 by the Jabber Software Foundation (JSF) and is in full conformance with the JSF's Intellectual Property Rights Policy <http://www.jabber.org/jsf/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-JIG discussion list: <http://mail.jabber.org/mailman/listinfo/standards-jig>.

Given that this JEP normatively references IETF technologies, discussion on the JSF-IETF list may also be appropriate (see <http://mail.jabber.org/mailman/listinfo/jsf-ietf> for details).

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 Jabber Software 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 JEP 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 keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

Table of Contents

1. Introduction

The Session Description Protocol (SDP; see RFC 2327 [1]) provides a mechanism for describing multimedia sessions that are advertised and negotiated over the Internet. The "Transport for Initiating and Negotiating Sessions" (TINS) specified herein describes how to use SDP to build a framework for media stream/session initiation and negotiation between entities that natively support XMPP (see RFC 3920 [2]). [3] In particular, TINS provides an XMPP representation of standard session management semantics such as those provided by the Session Initiation Protocol (SIP; see RFC 3261 [5]). As a result, native XMPP clients that support TINS can negotiate out-of-band multimedia sessions (e.g., use of the Real-Time Transport Protocol or RTP; see RFC 3550 [6]) and XMPP services that support TINS can easily interoperate with SIP services through gateways.

2. Requirements

This JEP addresses the following requirements:

1. Enable an XMPP entity to negotiate an out-of-band multimedia session with another XMPP entity.
2. Enable an XMPP entity to negotiate an out-of-band multimedia session with a non-XMPP entity through a gateway.
3. Maximize interoperability with existing gateways and devices by using standard Internet protocols.

3. Protocol

TINS exchanges are completed by sending <message/> stanzas containing a child <tins/> element qualified by the 'http://jabber.org/protocol/tins' namespace. [7] In order to track the structure of the TINS "conversation", the <thread/> child of <message/> MAY also be included. The <tins/> element MUST possess a 'method' attribute, whose value SHOULD be either an IANA-registered value for a SIP method or "result", as described below. The following SIP methods will probably be used most frequently in TINS interactions:

• INVITE -- Used to invite the target user to an out-of-band session. The content inside the <tins/> element MAY be SDP descriptions of the connection types offered. If a session is already established for this transaction, the new INVITE serves as a renegotiation of session parameters.

• ACK -- Used by the initiator to tell the invitee that an out-of-band session has been established.

• BYE -- Used by either side of the conversation to terminate the transaction. This message SHOULD cause all resources associated with this transaction to be freed, and any associated network connections to be terminated.

The SDP data itself is included as the XML character data of an <sdp/> child of the <tins/> element, qualifed by the 'urn:ietf:rfc:2327' namespace (this is consistent with RFC 2648 [8]). [9] Any restricted XML characters in the SDP data (i.e., & ' < > ") MUST be properly escaped when contained in the XML character data of the <sdp/> element (for example, the ' character MUST be escaped to &apos;). It is the responsibility of the XMPP recipient or translating gateway to unescape these restricted characters for processing.

The request stanza MAY also include either or both of the following:

• Header information or Internet metadata (such as that defined by RFC 3261) in the format specified by Stanza Headers and Internet Metadata (SHIM) [10].
• Multicast addresses as specified by Extended Stanza Addressing [11].

In reply to a request, the receiver MUST send zero or more replies, with the value of the 'method' attribute set to a value of "result" and the value of the 'code' attribute set to one of the valid SIP response codes as specified in Section 21 of RFC 3261.

4. Discovering Support

Before initiating a TINS negotiation, an XMPP entity SHOULD determine that the target entity supports the 'http://jabber.org/protocol/tins' namespace. Such discovery SHOULD occur by means of Service Discovery [12], either directly by querying the target entity or indirectly by means of Entity Capabilities [13]. If the target entity is a non-XMPP entity that is contacted through a gateway, the gateway itself SHOULD reply to service discovery queries on behalf of the non-XMPP entity and SHOULD insert a client capabilities extension into the presence stanzas it generates on behalf of the non-XMPP entity.

If an XMPP entity receives, or a gateway handles, a <message/> stanza containing a <tins/> element qualified by the 'http://jabber.org/protocol/tins' namespace but it does not understand the TINS protocol, it SHOULD either silently ignore it or return a <service-unavailable/> error (see Error Condition Mappings [14] for error syntax).

5. Examples

<message
    from='A@example.com/work' 
    to='B@example.com/laptop' 
    id='tins01'>
  <thread>1234@hostA.example.com</thread>
  <tins method='INVITE' xmlns='http://jabber.org/protocol/tins'>
    <sdp xmlns='urn:ietf:rfc:2327'>
      v=0
      o=A@example.com 98765432 IN IP4 192.168.1.1
      s=TINS questions
      i=Let&apos;s talk about TINS
      e=A@example.com
      p=+1-303-555-1212
      c=IN IP4 192.168.1.1/127
      t=3288361865 0
      a=recvonly
      m=audio 7800 RTP/AVP 0
    </sdp>
  </tins>
  <headers xmlns='http://jabber.org/protocol/shim'>
    <header name='Via'>SIP/2.0/UDP tins.example.com;branch=z9hG4bK776asdhds</header>
    <header name='Call-ID'>a84b4c76e66710@tins.example.com</header>
    <header name='CSeq'>314159 INVITE</header>
  </headers>
  <addresses xmlns='http://jabber.org/protocol/address'>
    <address type='bcc' jid='compliance.example.com'/>
  </addresses>
</message>
    

<message
    from='B@example.com/laptop' 
    to='A@example.com/work' 
    id='tins01'>
  <thread>1234@hostA.example.com</thread>
  <tins method='result'
        code='100'
        xmlns='http://jabber.org/protocol/tins'/>
  <headers xmlns='http://jabber.org/protocol/shim'>
    <header name='Via'>SIP/2.0/UDP tins.example.com;branch=z9hG4bK776asdhds</header>
    <header name='Call-ID'>a84b4c76e66710@tins.example.com</header>
    <header name='CSeq'>314159 INVITE</header>
  </headers>
  <addresses xmlns='http://jabber.org/protocol/address'>
    <address type='bcc' jid='compliance.example.com'/>
  </addresses>
</message>
    

<message
    from='B@example.com/laptop' 
    to='A@example.com/work' 
    id='tins01'>
  <tins method='result'
        code='180'
        xmlns='http://jabber.org/protocol/tins'/>
  <headers xmlns='http://jabber.org/protocol/shim'>
    <header name='Via'>SIP/2.0/UDP tins.example.com;branch=z9hG4bK776asdhds</header>
    <header name='Call-ID'>a84b4c76e66710@tins.example.com</header>
    <header name='CSeq'>314159 INVITE</header>
  </headers>
  <addresses xmlns='http://jabber.org/protocol/address'>
    <address type='bcc' jid='compliance.example.com'/>
  </addresses>
</message>
    

<message
    from='B@example.com/laptop' 
    to='A@example.com/work' 
    id='tins02'>
  <thread>1234@hostA.example.com</thread>
  <tins method='result' 
        code='200'
        xmlns='http://jabber.org/protocol/tins'>
    <sdp xmlns='urn:ietf:rfc:2327'>
      v=0
      o=A@example.com 98765432 IN IP4 192.168.1.2
      s=TINS questions
      i=Let&apos;s talk about TINS
      e=A@example.com
      p=+1-303-555-1212
      c=IN IP4 192.168.1.2/127
      t=3288361865 0
      a=recvonly
      m=audio 7800 RTP/AVP 0
      a=recvonly
      m=audio 9410 RTP/AVP 0
    </sdp>
  </tins>
  <headers xmlns='http://jabber.org/protocol/shim'>
    <header name='Via'>SIP/2.0/UDP tins.example.com;branch=z9hG4bK776asdhds</header>
    <header name='Call-ID'>a84b4c76e66710@tins.example.com</header>
    <header name='CSeq'>314159 INVITE</header>
  </headers>
  <addresses xmlns='http://jabber.org/protocol/address'>
    <address type='bcc' jid='compliance.example.com'/>
  </addresses>
</message>
    

<message
    from='A@example.com/work' 
    to='B@example.com/laptop' 
    id='tins02'>
  <thread>1234@hostA.example.com</thread>
  <tins method='ACK' xmlns='http://jabber.org/protocol/tins'/>
  <headers xmlns='http://jabber.org/protocol/shim'>
    <header name='Via'>SIP/2.0/UDP tins.example.com;branch=z9hG4bK776asdhds</header>
    <header name='Call-ID'>a84b4c76e66710@tins.example.com</header>
    <header name='CSeq'>314159 INVITE</header>
  </headers>
  <addresses xmlns='http://jabber.org/protocol/address'>
    <address type='bcc' jid='compliance.example.com'/>
  </addresses>
</message>
    

<message
    from='B@example.com/laptop' 
    to='A@example.com/work' 
    id='tins03'>
  <thread>1234@hostA.example.com</thread>
  <tins method='BYE' xmlns='http://jabber.org/protocol/tins'/>
  <headers xmlns='http://jabber.org/protocol/shim'>
    <header name='Via'>SIP/2.0/UDP tins.example.com;branch=z9hG4bK776asdhds</header>
    <header name='Call-ID'>a84b4c76e66710@tins.example.com</header>
    <header name='CSeq'>314159 INVITE</header>
  </headers>
  <addresses xmlns='http://jabber.org/protocol/address'>
    <address type='bcc' jid='compliance.example.com'/>
  </addresses>
</message>
    

<message
    from='A@example.com/work' 
    to='B@example.com/laptop' 
    id='tins03'>
  <thread>1234@hostA.example.com</thread>
  <tins method='result'
        code='200'
        xmlns='http://jabber.org/protocol/tins'/>
  <headers xmlns='http://jabber.org/protocol/shim'>
    <header name='Via'>SIP/2.0/UDP tins.example.com;branch=z9hG4bK776asdhds</header>
    <header name='Call-ID'>a84b4c76e66710@tins.example.com</header>
    <header name='CSeq'>314159 INVITE</header>
  </headers>
  <addresses xmlns='http://jabber.org/protocol/address'>
    <address type='bcc' jid='compliance.example.com'/>
  </addresses>
</message>
    

More examples to follow.

6. Security Considerations

TINS is subject to the same security considerations as XMPP, particularly with regard to authentication and channel encryption; for details, refer to RFC 3920.

This document does not describe how the media protocols (e.g. RTP) traverse firewalls and NATs.

There is no general-purpose way to ensure that media protocol connections are associated with the in-band TINS conversation.

7. IANA Considerations

This JEP requires no interaction with the Internet Assigned Numbers Authority (IANA) [15].

8. Jabber Registrar Considerations

9. XML Schemas

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='http://jabber.org/protocol/tins'
    xmlns='http://jabber.org/protocol/tins'
    elementFormDefault='qualified'>

  <xs:import namespace='urn:ietf:rfc:2327'/>

  <xs:element name='tins'>
    <xs:complexType>
      <xs:choice xmlns:sdp='urn:ietf:rfc:2327'>
        <xs:element ref='sdp:sdp'/>
        <xs:any namespace='##other'/>
      </xs:choice>
      <xs:attribute name='code' type='xs:string' use='optional'/>
      <xs:attribute name='method' type='xs:string' use='required'/>
    </xs:complexType>
  </xs:element>

</xs:schema>
    

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='urn:ietf:rfc:2327'
    xmlns='urn:ietf:rfc:2327'
    elementFormDefault='qualified'>

  <xs:element name='sdp' type='xs:string'/>

</xs:schema>
    

Notes

Revision History

END