The repeater can connect the cables of two LANs, re-time and regenerate the digital signals on the cables, and then send them out. These functions are typical of the physical layer, the first layer in the OSI model. The function of the repeater is to increase the coverage area of the LAN. For example, the Ethernet standard stipulates that the maximum length of a single section of signal transmission cable is 500 meters. However, after connecting five sections of cables with the repeater, the maximum length of the signal transmission cable in the Ethernet can reach 2500 meters. Some brands of repeaters can connect cable segments with different physical media, such as thin coaxial cables and optical cables.

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.