A system has a transmitter for transmitting a sequence of packets, the transmitter has a first counter for storing a first sequence number, a first generating unit for generating an error check code for checking an error in each of the packets on the basis of the header and the data in each of the packets and the first sequence number, and a transmitting unit for transmitting each of the packet together with each of the error check code and a receiver has a second counter for storing a second sequence number, a second generating unit for generating an error check code for checking an error in each of the packets on the basis of the header and the data in each of the packets received from the transmitter and the second sequence number and an error check unit for checking an error in the sequence of the packet.