%ents; ]>
A Transport for Initiating and Negotiating Sessions (TINS) This document defined a SIP-compatible transport for initiating and negotiating sessions using SDP over XMPP. &LEGALNOTICE; 0111 Retracted Standards Track Standards Council XMPP Core RFC 2327 RFC 3261 XEP-0166 tins &hildjj; &stpeter; 0.8 2005-12-21 psa/jjh Retracted in favor of Jingle (XEP-0166). 0.7 2005-05-12 psa Corrected several errors in the text and schemas. 0.6 2004-10-26 psa/jjh Added extended addresses and SHIM headers to examples in order to illustrate the use of XEP-0033 and XEP-0121. 0.5 2004-04-05 psa/jjh Changed <iq/> to <message/> given probability of multiple SIP responses. 0.4 2004-03-16 psa/jjh Specified that the <sdp/> element is in a separate namespace and that the same mechanism could be used for other content schemes in the future. 0.3 2004-03-15 psa/jjh Replaced SDPng with SDP; added sections for Requirements, Protocol, and Discovering Support; added XML schema. 0.2 2003-07-29 psa Converted to XML format. 0.1 2003-02-21 jjh Internet-Draft version published as draft-hildebrand-xmpp-sdpng-00.

Note Well: This proposal has been retracted by the authors in favor of &xep0166;.

The Session Description Protocol (SDP; see &rfc2327;) 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 &xmppcore;). The approach taken herein is to send pure SDP. While earlier versions of this document used &sdpng; (an XML representation of SDP), SDPng is a more experimental technology; by contrast, SDP is a stable protocol and there is broad support for it by existing gateways and devices. The use of SDP rather than SDPng thus enables the Jabber/XMPP community to implement solutions that are deployable on the Internet today. In particular, TINS provides an XMPP representation of standard session management semantics such as those provided by the Session Initiation Protocol (SIP; see &rfc3261;). 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 &rfc3550;) and XMPP services that support TINS can easily interoperate with SIP services through gateways.

This document 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.

TINS exchanges are completed by sending &MESSAGE; stanzas containing a child <tins/> element qualified by the 'http://jabber.org/protocol/tins' namespace. While it may seem that the semantics of &IQ; stanzas are more appropriate, RFC 3261 allows entities to send multiple results in response to a SIP request, which does not map to the syntax of the &IQ; stanza as defined in RFC 6120. 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:

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 &rfc2648;). The <sdp/> element is qualified by a separate namespace because it may be desirable for TINS to support other formats (such as SDPng) in the future; these can then be added without changing the XML schema for TINS. 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:

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.

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 &xep0030;, either directly by querying the target entity or indirectly by means of &xep0115;. 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 &unavailable; error (see &xep0086; for error syntax).

The following XMPP stanzas could be used to initiate a voice call. The 'from' addresses will usually be added by the XMPP server or relevant gateway, but are shown here for the sake of clarity. Note the inclusion of SHIM headers and extended addresses.

1234@hostA.example.com v=0 o=A@example.com 98765432 IN IP4 192.168.1.1 s=TINS questions i=Let'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
SIP/2.0/UDP tins.example.com;branch=z9hG4bK776asdhds
a84b4c76e66710@tins.example.com
314159 INVITE
]]> 1234@hostA.example.com
SIP/2.0/UDP tins.example.com;branch=z9hG4bK776asdhds
a84b4c76e66710@tins.example.com
314159 INVITE
]]>
SIP/2.0/UDP tins.example.com;branch=z9hG4bK776asdhds
a84b4c76e66710@tins.example.com
314159 INVITE
]]> 1234@hostA.example.com v=0 o=A@example.com 98765432 IN IP4 192.168.1.2 s=TINS questions i=Let'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
SIP/2.0/UDP tins.example.com;branch=z9hG4bK776asdhds
a84b4c76e66710@tins.example.com
314159 INVITE
]]> 1234@hostA.example.com
SIP/2.0/UDP tins.example.com;branch=z9hG4bK776asdhds
a84b4c76e66710@tins.example.com
314159 INVITE
]]> 1234@hostA.example.com
SIP/2.0/UDP tins.example.com;branch=z9hG4bK776asdhds
a84b4c76e66710@tins.example.com
314159 INVITE
]]> 1234@hostA.example.com
SIP/2.0/UDP tins.example.com;branch=z9hG4bK776asdhds
a84b4c76e66710@tins.example.com
314159 INVITE
]]>

More examples to follow.

TINS is subject to the same security considerations as XMPP, particularly with regard to authentication and channel encryption; for details, refer to RFC 6120.

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.

This document requires no interaction with &IANA;.

The ®ISTRAR; shall include 'http://jabber.org/protocol/tins' in its registry of protocol namespaces.

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