Abstract: This invention proposes a mobility management method and system for wireless data networks, such as GPRS and UMTS systems. The wireless data network consists of at least one mobile device and one network apparatus. The cells in a wireless data network are partitioned into several routing areas. In the wireless data network, the mobility management activities for a mobile device are characterized by a mobility management finite state machine exercised in both the mobile device and network apparatus. There are three states in the machine: idle state, standby state and ready state. Both the mobile device and network apparatus employ a ready counter, which counts the number of cells crossed by the mobile device in the packet idle period between two packet transmissions. If the counted number reaches a threshold, the mobility management state switches from the ready state to standby state.

Abstract: A magnetic recording and reproducing apparatus having a reproducing circuit structure which improves a high frequency characteristic of a reproduction signal output from a read head. The read head reads information recorded on a recording medium. A first amplifying circuit amplifies a reproduction signal generated by the read head. A second amplifying circuit, which comprises a high-frequency amplifying circuit, amplifies the reproduction signal amplified by the first amplifying circuit in a high-frequency amplifying manner. The first amplifying circuit and the second amplifying circuit together constitute a cascode amplifier. A third amplifying circuit amplifies the reproduction signal amplified by the second amplifying circuit. A reproducing circuit reproduces the reproduction signal amplified by the third amplifying circuit.

Abstract: A reproducing head is moved by a moving stand along the diameter at a constant speed. At this time, an in-focus detecting circuit waits until the cancellation of the focus control. The time to the cancellation of the focus control is counted by a microprocessor. Based on the time, the microprocessor discriminates the radius of an information recorded disk.