IP Multimedia System (IMS) centralized services
This document contains the results of the feasibility study into the architectural requirements and alternatives for the delivery of consistent services to the user mainly via IMS centralized services regardless of the attached access type; e.g. CS domain access or IP-CAN. Considerations include overall requirements, architectural requirements, alternative architectures and evaluation of potential architectural solutions.
The study considers how to access IMS-based multimedia telephony services while still allowing innovative services. It includes investigation into call/session establishment via CS domain access and IP-CAN and for calls/sessions transferred across CS domain access and IP-CAN, including the interactions with domain selection. It provides consideration for the handling of the multiple medias that are enabled by the multimedia telephony communication service. The solution should be applicable for terminals with VCC capabilities and for non-VCC capable terminals. Impact on legacy terminals with the same subscription (e.g. SIM swapping) should be studied.
The second objective of the study is an investigation into the means to support and the need of the evolution of a network towards the IMS centralized services architecture. The assumption for this evolution is that some networks may not immediately migrate all services to the IMS centralized services architecture. In addition, given that some calls may not be rerouted to IMS during the migratory period, the study shall also investigate how to ensure that equivalent services are implemented in IMS and CS.