Packet pre-processing unit which checks received packet validity and redundancy

A packet pre-processing unit receives a data packet containing header information and application data, checks the validity of the packet by reference to stored subscription data using header data for the IP destination address, destination port and VLAN tag, checks whether the application data has already been received, and only outputs the packet for further processing if the packet is valid and doesnt contain redundant application data, thereby reducing the load of the memory, bus, and CPU of the computer system.