Patent ID: 8179850

Claim:
A mobile communication system in which a mobile station shifts from a first communication state to a second communication state, the first communication state being a state in which the mobile station performs high speed downlink packet communication by using a high speed downlink packet communication compliant radio link, and performs uplink packet communication by using at least one radio link not including a high speed uplink packet communication compliant radio link, the second communication state being a state in which the mobile station performs the high speed downlink packet communication by using the high speed downlink packet communication compliant radio link, and performs high speed uplink packet communication by using the high speed uplink packet communication compliant radio link, wherein when at least one high speed uplink packet communication compliant radio link is established by the mobile station in the first communication state, the mobile station in the first communication state shifts to the second communication state, wherein when at least one high speed uplink packet communication compliant radio link is established by the mobile station in the first communication state, and when an amount of data in a transmission buffer of the mobile station in the first communication state exceeds a predetermined threshold value, the mobile station in the first communication state shifts to the second communication state.