A process cartridge is detachably mountable to a main assembly of an electrophotographic image forming apparatus. The multiplier outputs a spread signal obtained by multiplying a data sequence by the spread code sequence to an impulse generator. The time difference of arrival for is found for each receiver relative to a predetermined reference receiver. The internal cavity has at least one partition member disposed therein that is lying generally parallel to the bottom face. The method measures tangential and vertical forces acting on an elastic body 3 of an elastic wheel 1, and calculates the friction coefficient of a road surface based on the measured values of these forces and angular rate of the wheel 1. The method inserts OpenFlow OAM packets into an OpenFlow data flow to monitor the OpenFlow data flow, wherein inserted OpenFlow OAM packets have fate sharing with data packets in the OpenFlow data flow.