A memory device of a resistance variation type, in which data retaining characteristic at the time of writing is improved, is provided. The invention is based on measuring the traffic flow that comes to be scheduled, in which the flow is formed of packets representing a specific service level class arriving in the queue, or some of the relevant packets, and on controlling the operation of the scheduler and congestion limitation mechanism on the basis of the measurement results. Controlled availability and generation of the keys required for encryption and decryption of data is such that even if back doors are accessed that previously encrypted data is impossible to decrypt and thus worthless even if a back door is found and maliciously pried open. The second stopping device preferably includes centrifugally activated components such as a latch member that moves from a first position into a second, stopping position responsive to an undesirably high speed of upward movement of the elevator cab.