Patent ID: 8588771

Claim:
Method of providing access to an IP multimedia subsystem for a subscriber communicating in an access communication network and requesting access to said IP multimedia subsystem through a home interface entity located in the home communication network of said subscriber, said IP multimedia subsystem being a packet switched based domain located in said home communication network and comprising serving means for home subscribers storing profile data of said subscriber and home network data identifying said home communication network and call state control functionality means controlling service calls within said IP multimedia subsystem, the method comprising the steps of: providing said home interface entity with access network data identifying said access communication network; sending a message comprising said access network data from said home interface entity to said serving means; comparing said home network data and said access network data in said home communication network of said subscriber; checking if said subscriber is allowed to roam based on a set of predefined criteria when the result of said comparing step is false; sending a message comprising said access network data to at least one of said call state control functionality means when the result of said checking step is true.