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TR 23.894 (SA2)
System enhancements for the use of
IMS services in local breakout and optimal routeing of media

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(W-zip) V10.0.0    2009/12    59 p.

Rapporteur:  Mr. Madella, Mario
See also:  –

Due to the increasing volume of data traffic exchanged by mobile users and the rapid decrease of roaming rates that is being imposed by the regulator, mobile operators will most likely have to revisit their roaming agreements, moving towards a more extensive usage of local breakout. This will allow to reduce the cost per bit of data traffic exchanged by roaming customers, since at least part of it will be handled directly by the visited operator, with no need to waste bandwidth on the international links between home and visited networks; moreover, local breakout would allow to offer better performance to the customers.

Based on the analysis of the requirements on local breakout and on the increasing number of the services controlled by IMS that operators are expected to face, it has been proposed that system enhancements are needed to enable extensive usage of IMS services in local breakout.

Furthermore, international communications and terminal roaming introduce a number of scenarios where sessions may traverse multiple IMS networks. The use of Border Control Function makes both the signalling and bearer path traverse through the same networks path and could make the media path not optimized.

In order to ensure Quality of Service (QoS) and, in certain cases, minimal routeing costs, there is a need to enable the routeing of media traffic via an optimal path between those networks, without necessarily being linked to the path that the signalling flow needs to take. The optimal media path between two endpoints may involve IP transit networks, which in normal circumstances are not included in the SIP signalling path. Current QoS reservation is negotiated based on the SIP pre-conditions model, and hence the lack of SIP signalling in the transit network presents a problem for the negotiation of QoS between the end-points.

This study intends to investigate the general problem of system enhancements for the use of IMS services in local breakout and optimal routeing of media.


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1   Scope   Word-p. 6
2   References   Word-p. 7
3   Definitions and abbreviations
4   Overall Requirements
5   Architectural Requirements and Assumptions   Word-p. 8
6   Scenarios and Solutions for local breakout   Word-p. 9
7   Scenarios and Solutions for optimal routeing of media
7.1   Scenarios
7.2   Alternative 1: Extension to SDP for TrGW bypass   Word-p. 16      Up
7.3   Alternative 2: Transcoding aware   Word-p. 29
8   Evaluation of the Solutions   Word-p. 39
9   Conclusions   Word-p. 40
A   OMR use cases   Word-p. 42
B   Interconnect Assumptions   Word-p. 55      Up
C   Change history   Word-p. 59

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