TINS: A Transport for Initiating and Negotiating Sessions using SDPng over XMPP

The MMUSIC WG has defined an XML format for Session Description and Capability Negotiation (SDPng). Given the availability of a native XML transport in the form of the Extensible Messaging and Presence Protocol (XMPP), it may be valuable to explore how to build a framework for media stream/session initiation and negotiation over XMPP. This document explores such a framework, with SDPng over XMPP providing a semantics for signalling call setup that is similar to the semantics alternatively provided by the Session Initiation Protocol (SIP).

This document inherits terminology defined in SDPng and in XMPP Core. The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

The author welcomes discussion and comments related to the topics presented in this document. The preferred forum is the <xmppwg@jabber.org> mailing list, for which archives and subscription information are available at <http://www.jabber.org/cgi-bin/mailman/listinfo/xmppwg/>.

This document is in full compliance with all provisions of Section 10 of RFC 2026.

The following is an example flow of XMPP stanzas to initiate a call. The from addresses will usually be added by the XMPP server, but are shown for clarity.

Step 1: A sends an invite to B: 1234@hostA.example.com This message contains a TINS invite, but your client does not support TINS. Telephony media stream ]]>

Step 2: B tells A that it is trying: 1234@hostA.example.com ]]>

Step 3: B tells A that it is ringing: 1234@hostA.example.com ]]>

Step 4: B sends A updated description: 1234@hostA.example.com ]]>

Step 5: A sends an ACKnowldgement: 1234@hostA.example.com ]]>

Step 6: B hangs up: 1234@hostA.example.com ]]>

Step 7: A acknowledges the hang up: 1234@hostA.example.com ]]>

The <thread/> element from XMPP is used to group TINS messages together into a shared context. A unique thread value MUST be used for each transaction. An example of a transaction might be a single voice call.

The following methods can be used in a TINS message.

Invite the target user to an out-of-band session. The content inside the <tins/> element MAY be SDPng 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.

The initiator tells the invitee that an out-of-band session has been established.

Either side of the conversation decides 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.

In reply to each of the method messages, the receiver sends 0 or more replies, with the method set to 'result'. Result codes are as specified in RFC 3261, section 21.

TINS is subject to the same security considerations as XMPP, particularly with regard to authentication and channel encryption. 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.

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