Content for  TS 29.079  Word version:  18.0.0

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1  Scopep. 6

The present document defines optional Optimal Media Routeing (OMR) procedures that can be applied by entities in the IP Multimedia Subsystem (IMS) that control media resources and are capable of manipulating the Session Description Protocol (SDP) as defined by RFC 4566.
The OMR procedures in the present specification relate to the handling of OMR-specific SDP attributes that are documented in TS 24.229. The OMR procedures use SDP offer/answer related procedures in RFC 3264 and in TS 24.229 in a backward-compatible manner.
The 3GPP network architecture, including the configuration and network entities of the IMS, is defined in TS 23.002. The Stage 2 of the IMS is defined TS 23.228. Annex Q of TS 23.228 documents the architecture and call flows for OMR.
The OMR procedures in this document are applicable to the following IMS entities that perform as an IMS-ALG or UA according to TS 24.229 and that control media resources:
  • an IBCF acting as an IMS-ALG;
  • a P-CSCF acting as IMS-ALG;
  • an AS acting as B2BUA and adapting IMS-ALG procedures to control an MRF;
  • an AS acting as B2BUA and adapting UA procedures to control an MRF; and
  • an MGCF acting as UA.
The OMR procedures are not applicable for an UE.

2  Referencesp. 6

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
  • References are either specific (identified by date of publication, edition number, version number, etc.) or non-specific.
  • For a specific reference, subsequent revisions do not apply.
  • For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
TR 21.905: "Vocabulary for 3GPP Specifications".
TS 23.002: "Network architecture".
TS 23.228: "IP multimedia subsystem; Stage 2".
TS 24.229: "IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3".
RFC 3264:  "An Offer/Answer Model with Session Description Protocol (SDP)".
RFC 4566:  "SDP: Session Description Protocol".
[7]  Void.
RFC 3605:  "Real Time Control Protocol (RTCP) attribute in Session Description Protocol (SDP)".
TS 29.238: "Interconnection Border Control Functions (IBCF) - Transition Gateway (TrGW) interface, Ix Interface; Stage 3".
TS 29.334: "IMS Application Level Gateway (IMS-ALG) - IMS Access Gateway (IMS-AGW); Iq Interface; Stage 3".
RFC 4240:  "Basic Network Media Services with SIP".
RFC 3260:  "Media Control Channel Framework".
RFC 6505:  "A Mixer Control Package for the media Control Channel Framework".
TS 29.332: "Media Gateway Control Function (MGCF) - IM Media Gateway Mn Interface".
TS 23.334: "IP Multimedia Subsystem (IMS) Application Level Gateway (IMS-ALG) - IMS Access Gateway (IMS-AGW) interface: Procedures descriptions".
TS 29.162: "Interworking between the IM CN subsystem and IP networks".
TS 29.163: "Interworking between the IP Multimedia (IM) Core Network (CN) subsystem and Circuit Switched (CS) networks".
RFC 5552:  "SIP Interface to VoiceXML Media Services".
RFC 4117:  "Transcoding Services Invocation in the Session Initiation Protocol (SIP) Using Third Party Call Control (3pcc)".
RFC 5939:  "Session Description Protocol (SDP) Capability Negotiation".
RFC 2234:  "Augmented BNF for Syntax Specification: ABNF".
RFC 7549:  3GPP SIP URI Inter Operator Traffic Leg parameter".

3  Definitions, symbols and abbreviationsp. 7

3.1  Definitionsp. 7

For the purposes of the present document, the terms and definitions given in TR 21.905, 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.
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.
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  Symbolsp. 8

For the purposes of the present document, the following symbols apply:
Reference Point between IBCF and TrGW
Reference Point between the P-CSCF and the IMS Access Gateway

3.3  Abbreviationsp. 8

For the purposes of the present document, the abbreviations given in TR 21.905, in TS 23.228 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 or in TS 23.228.
Application Level Gateway
Back-to-Back User Agent
Interactive Connectivity Establishment
Media Resource
Optimal Media Routeing
Transit and Roaming Function
User Agent

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