Partitioned IP multimedia subsystem call session control function

A network system of a network service provider for providing IP Multimedia Subsystem (IMS) service to users within a leasing entity, the leasing entity providing a media application to the users, the network system comprising:

• a plurality of network elements connected to form a core domain operated by the network service provider;
• a master IMS instance configured within the core domain and including a core call session control function (CSCF) with a master CSCF address;
• a partitioned IMS instance configured as a virtual core within the core domain and including 1) a partitioned CSCF with a partitioned CSCF address accessible by the users from outside the core domain and 2) a leasing-entity home subscriber server (HSS) storing user profiles identifying an application server providing the media application, wherein the leasing-entity HSS is accessed to obtain a corresponding user profile when a user of the leasing entity accesses the partitioned IMS using the partitioned CSCF address;
• and
• an IMS service control interface between the master IMS instance, the partitioned IMS instance, and the application server so that the partitioned CSCF has access to the core CSCF via the master CSCF address for establishing transfer of media according to the media application as defined in the user profile.