As the packet switched radio networks capabilities evolve, they become more and more attractive media for carrying also real time speech traffic such as the traditional TS11 and TS12. In order to make the best use of such resources access from the deployed CN infrastructure and services should be possible. This will allow avoiding a major switch in the voice call control paradigm as well as retaining the currently provided functionalities such as the charging mechanisms (calling party pays), supplementary services provision and so on. As the circuit switched network will continue to be employed in the future, also handover needs to be taken into account. Give the proven track record of the current call control, this TR intends to investigate architectures suitable to support CS Domain Services over new types of accesses and manage the handover of calls from a traditional bearer to the new available ones. The study also aims to ensure that the user experience remains as consistent and as satisfactory as it is today.

The present document contains the results of the study of the architectural requirements of CS Domain Services over evolved PS access and concludes with a way forward. Considerations include overall requirements, architectural requirements, evaluation of potential architectural solutions and alternative architectures. The objective is to describe an architecture that is capable of extending the 'traditional' MSC-Server based set of CS voice, supplementary and value-adding services and business principles (e.g. for roaming and interconnect) to the evolved PS access. The intention is also to give a CS handover-like user experience for voice calls when changing between evolved PS and legacy CS accesses. The architecture will however not be limited to the provision of speech services over evolved PS accesses; on the contrary, through the exploitation of the Combinational services, it will be possible to harness the capabilities of IMS to provide new, innovative services to the end user. Handover of the parallel PS session towards legacy 3GPP access will be considered as well, but may be limited by the capabilities of the legacy system and operator preferences. Co-existence with IMS centric Single Radio VCC solutions shall be studied as well.

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.