Patent ID: 8208902

Claim:
A communication system comprising: a radio terminal configured to perform handover from a first radio base station to a second radio base station; a first authentication server configured to perform authentication of a first access to a communication network via the first radio base station; and a second authentication server configured to perform authentication of a second access to the communication network via the second radio base station, wherein upon detection of a radio signal including a base station identifier identifying the second radio base station during the first access, the radio terminal notifies the first authentication server of the base station identifier, and the first authentication server includes: a storage unit configured to store a usable base station identifier identifying a usable base station which is a radio base station usable by the radio terminal to access the communication network; a request transmitter configured to transmit, to the second authentication server, an authentication request requesting authentication of the second access of the radio terminal, when the base station identifier notified by the radio terminal matches the usable base station identifier stored by the storage unit; and a notification transmitter configured to transmit, to the radio terminal via the first radio base station, a permit notification indicating that the second access is permitted, when the second authentication server permits the second access of the radio terminal in response to the authentication request, wherein upon receipt of the permit notification, the radio terminal performs the handover to the second radio base station and starts the second access.