Due to the influence of transmission line noise, the digital signal or analog signal carrying information can only transmit a limited distance. The function of the repeater is to regenerate and transmit the received signal, thus increasing the distance of signal transmission. It connects two or more network segments of the same network. For example, Ethernet often uses repeaters to extend the cable length of the bus. The maximum length of each segment of standard thin cable Ethernet is 185 meters, and the maximum length can be 5 segments. Therefore, after adding repeaters, the maximum network cable length can be increased to 925 meters. Generally speaking, the network segments at both ends of the repeater are network segments, not subnets.

Repeaters are connecting devices that work on the physical layer. It is applicable to the interconnection of two identical networks. Its main function is to expand the network transmission distance by retransmitting or forwarding data signals. Repeaters are network devices that regenerate and restore signals: physical layer devices of OSI model.