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.

Repeater is a device that connects network lines and is often used for two-way forwarding of physical signals between two network nodes. The repeater mainly completes the function of the physical layer, is responsible for transmitting information bitwise on the physical layer of the two nodes, and completes the function of signal replication, adjustment and amplification to extend the length of the network. Due to the loss, the signal power transmitted on the line will gradually attenuate. When it attenuates to a certain extent, it will cause signal distortion, and thus lead to receiving error. The repeater is designed to solve this problem. It completes the connection of the physical circuit, amplifies the attenuated signal, and keeps the same as the original data. Generally, the two ends of the repeater are connected to the same media, but some repeaters can also complete the transfer of different media. Theoretically, the use of repeaters is unlimited, so the network can be extended indefinitely. In fact, this is impossible, because the network standard has specified the delay range of the signal, and the repeater can only work effectively within the specified range, otherwise it will cause network failure.