A system, method, and computer readable medium for processing registration and authentication procedures by an IP-based femtocell system are provided. The femtocell system includes a base transceiver station and a Session Initiation Protocol to Internet Operating System adapter. The femtocell system receives a registration message from a user equipment, issues a location update request on behalf of the user equipment, transmits a register message to a core network, receives an authentication request from the core network, and transmits an authentication challenge to the user equipment.