Method and device for discovering and synchronizing service capabilities

A radio terminal adapted to communicate with an IP Multimedia subsystem of a cellular communication system, said cellular communication system furthermore comprising a Multimedia Telephony application server communicatively coupled to the IP Multimedia subsystem, wherein:

• the radio terminal is adapted to transmit a REGISTER message comprising an option tag indicating support of a network based service by the radio terminal to the IP Multimedia subsystem, said option tag requesting information whether said network based service is supported by said cellular communication system;
• the radio terminal is adapted to receive a positive acknowledge message from the IP Multimedia subsystem,
• the IP Multimedia subsystem transmits a third party REGISTER message to the Multimedia Telephony application server, said third party register message comprising the full REGISTER request and comprising the positive response message;
• the radio terminal is adapted to receive a message request from the IP Multimedia subsystem after the IP Multimedia subsystem transmitted a third party REGISTER message comprising the full REGISTER request and the positive acknowledge message to the Multimedia Telephony application server, said Multimedia Telephony application server transmitted a corresponding message request indicating support of the network based service to the Multimedia subsystem in return to the third party REGISTER message;
• and
• the radio terminal is adapted to update a local variable corresponding to the indicated support of the network based service upon receipt of the message request.

A method for registering a network based supplementary service in a cellular communication system comprising an IP Multimedia subsystem and a Multimedia Telephony application server, coupled to the IP Multimedia subsystem, the method comprising:

• receiving a REGISTER message from a radio terminal by the IP Multimedia subsystem, said REGISTER message comprising an option tag indicating a network based service supported by the radio terminal and said option tag requesting information whether said network based service is supported by the cellular communication system;
• acknowledging said REGISTER message by transmitting an positive response message to the radio terminal by the IP Multimedia subsystem;
• transmitting a third party REGISTER message to the Multimedia Telephony application server by the IP Multimedia subsystem, said third party register message comprising the full REGISTER request and comprising the positive acknowledge message;
• transmitting a positive response message to the IP Multimedia subsystem indicating receipt of the third party REGISTER message the Multimedia Telephony application server;
• transmitting a message request to the IP Multimedia subsystem, the Multimedia Telephony application server, said message request indicating support of the network based service by the Multimedia Telephony application server;
• forwarding the message request to the radio terminal by the IP Multimedia subsystem;
• updating a local variable corresponding to the indicated support of the network based service upon receipt of the message request and to transmit a positive acknowledge message to the IP Multimedia subsystem by the radio terminal;
• forwarding the positive acknowledge message to the Multimedia telephony application server, the IP Multimedia subsystem ;
• and
• updating a user profile associated with the radio terminal corresponding to the positive acknowledge message of the radio terminal forwarded by the IP Multimedia subsystem by the Multimedia Telephony application server.