CFP4 is an optical transceiver module to transmit and receive light or electricity information. It is an upgraded version of CFP2 which reaches a smaller size of only 21mm width, that is one quarter the size of CFP and half the size of CFP2. CFP4 is applied for 100G Ethernet communication and long distance transmission up to 10km. In view of the better functionality of CFP4, it costs much higher than the average transceivers, thus is not so commonly used by ordinary people. In the future, when technology matures, it may be available as the mainstream product for a 400G network.