3 Definitions, symbols and abbreviations

29.0793GPPOptimal media routeing within the IP Multimedia Subsystem (IMS)Release 17Stage 3TS

3.1 Definitions

For the purposes of the present document, the terms and definitions given in TR 21.905 [1], and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905 [1].

Codec: A media configuration for a media line in SDP that is specified by one or more formats in the format list of the m-line, by one or more preferred configurations (pcfg) associated with the media line, or by a combination of both.

Codec Change: Any modification to the media configurations for the media line in the format list or the list of preferred configurations.

Codec List: Either the format list of the m-line, or a combination of all the preferred configurations and the format list for the media line.

Connected IP realm: Compared to a reference IP realm, a connected IP realm is one identified with a different unique name where all IP endpoints in the two IP realms are mutually reachable (accessible) by means of IP routeing without address translation. Interconnection between the IP realms may be via direct link, via IP tunnel through other networks, via IP routeing through intermediate networks, or via any other method of internetworking as long as their IP endpoints are mutually reachable. The property of connectedness is symmetric but not necessarily transitive. In particular, two IP realms connected to a reference IP realm are not necessarily themselves connected.

Incoming termination: The termination at an MR in the direction from where an incoming SDP offer is being received at the IMS-ALG that is controlling the MR.

IP realm: A collection of IP endpoints identified by a unique name, where all IP endpoints are mutually reachable by means of IP routeing without address translation.

Media resource: An IMS Network entity that provides resources to process media streams and is controlled by an entity applying OMR procedures. A TrGW, BGW, MRF, or a function internal to the entity performing OMR can be a media resource.

Loopback routeing: A method of routeing a SIP request back to the visited network for local breakout according to the Roaming Architecture for Voice over IMS with Local Breakout as specified in TS 24.229 [4].

Outgoing termination: The termination at an MR in the direction towards where an outgoing SDP offer is being sent at the IMS-ALG that is controlling the MR.

Second SDP offer/answer: An SDP offer/answer transaction initiated by any of the involved IMS-ALGs during session establishment towards the initial SDP answerer upon reception of the initial SDP answer and MR resources are required (e.g. when an intermediate IMS-ALG performs proactive transcoding without resource reservation) or not required (e.g. when MR resources are reserved for the purpose of transcoding and transcoding is not required). The second SDP offer is not an end-to-end negotiation and is handled as the initial SDP offer.

Subsequent SDP offer/answer: An end-to-end SDP offer/answer transaction initiated after a completed initial or second SDP offer/answer transaction. The subsequent SDP offer contains no OMR specific attributes.

3.2 Symbols

For the purposes of the present document, the following symbols apply:

Ix Reference Point between IBCF and TrGW

Iq Reference Point between the P-CSCF and the IMS Access Gateway

3.3 Abbreviations

For the purposes of the present document, the abbreviations given in TR 21.905 [1], in TS 23.228 [3] and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905 [1] or in TS 23.228 [3].

ALG Application Level Gateway

B2BUA Back-to-Back User Agent

IC Interconnection

ICE Interactive Connectivity Establishment

MR Media Resource

OMR Optimal Media Routeing

TRF Transit and Roaming Function

UA User Agent