During the definition of IMS, 3GPP has adopted the approach of defining a number of IMS enablers to be used by a number of services. The adoption of the IMS by other standardisation bodies such as OMA, TISPAN and ATIS is a testament to the success of this approach. With a system that supports a number of services on a common set of enablers leads to the need of identifying the communication service that is being invoked. This technical report captures the results of a feasibility study into the identification of IMS communication services with a focus on the application of an IMS communication service identifier and the necessary administrative procedures. A brief summary of the needs to identify a IMS communication service include:

• the IMS network is required to identify the correct application server(s) to link into the SIP call path over the ISC, when an application server is required;
• the media authorization policy may use a communication service identifier as input;
• it is desirable for the network to be able to authorize the use of a communication service;
• charging may use a communication service identifier as input;
• in a multi-UE scenario where a recipient has several UEs with different UE capabilities, it is useful to be able to route the SIP request to the UE(s) supporting a requested communication service;
• in order to enable the User Equipment to identify the correct application logic, while allowing for many services to be offered using the same enablers and media types;
• often interworking requires knowledge of the services being interworked, as such interworking between an IMS based service and a non-IMS based service may benefit from the identification of the requested communication service;
• allowing the network to authorise the use of the service for a particular user;
• communication service prioritisation in the case of network overload;
• to be an input into inter-operator interconnect service level agreements;
• provide a scope for the IOP specifications related to a particular communication service.

The scope of the technical report is to capture the results of a feasibility study in the needs of identifying IMS communication services with and in the need of the IMS communication service identifier. This technical report contains the results into a study on the communication service identifier with a focus on the following aspects:

• a frame work description for the usage and applicability of the communication service identifier and its relationship with the PSI and other existing IMS mechanisms;
• identifying the architectural requirements for a communication service identifier that enable the usage scenarios identified in the above justification section;
• identifying requirements on compatibility and evolution of a communication service in relation to the communication service identifier;
• identify the methods for administrative procedures for a communication service identifier, including the requirements upon when a service identifier value is required to be allocated;

In addition alternative mechanisms to identify communication services may be identified.