Patent ID: 10383163

Abstract:
A method of determining in an IP multimedia subsystem, IMS, network which radio access type, RAT, should be used to route a terminating session directed towards a user equipment, UE. The HSS receives a terminating access domain selection, T-ADS, query from an application server, AS, of the IMS network, the T-ADS query relating to the terminating session and identifying the UE; and determines whether a packet data network gateway, PDN-GW, is registered for the UE. In the case where a PDN-GW is registered, the HSS sends a RAT request towards the PDN-GW, the RAT request identifying the UE and requesting a RAT used by the UE to connect to the IMS network. The PDN-GW determines the RAT and sends the result towards the HSS, which sends a T-ADS response to the AS indicating the RAT. In the case where a PDN-GW is not registered, the HSS sends a T-ADS response to the AS indicating that the RAT is a circuit switched RAT. Apparatus for implementing the method are also provided.