Patent ID: 8352838

Claim:
A cipher processing device which performs cipher processing on a packet combining data unit that is transmitted from a mobile station of a mobile communication system and received at a base station, the cipher processing device comprising: a MAC (Media Access Control) loss detecting/estimating section which detects occurrence of loss in protocol data units created by dividing the packet combining data unit for each logic channel by a MAC SDU (service data unit) generating section included in advance based on information of the logic channels which specify radio bearers contained in the packet combining data unit, and estimates the radio bearer of a lost protocol data unit and a data amount of the lost protocol data unit; an RLC (Radio Link Control) loss detecting/estimating section which detects occurrence of loss in the protocol data units when putting together the divided protocol data units into a service data unit for a higher-level device, and estimates a lost amount of the protocol data units when making the service data unit based on the data amount estimated by the MAC loss detecting/estimating section; and a correction section which corrects a frame number of the service data unit based on the estimated data amount from the RLC loss detecting/estimating section.