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A network device refers to a component that is used to connect computers in a network. The following are some commonly used network devices:
Repeater: It is a two-port signal regenerator that is used to extend the length of an Ethernet cable. It produces the original bit pattern for the attenuated signal it receives. It works at the physical layer.
Bridge: It connects two or more LANs. It operates at both physical and data link layers to regenerate the input signals and filter the frames respectively. It filters frames on the basis of a table containing MAC addresses of every node and the port number. It checks for the MAC addresses of the source and destination node contained in a frame and decides or forwarding or dropping the frame.
Hub: It contains several ports for connecting multiple computers to form a small network. A simple hub is also called concentrator. It works at the physical layer of OSI model where it connects several segments of a LAN together or multiple workstations in a single LAN.
Switch: It connects two network segments as well as various LANs and WANs together
Router: It connects two networks together and ensures routing of data between nodes and networks. A router has a routing table containing source and destination addresses. On receiving a data packet, the router seeks the destination address from the routing table and ensures the best route of data around network. Having data that, it proceeds to forward the data packet to its appropriate destination. It works on the network layer of OSI Model.
Gateway: It connects more than one network that uses different protocols. It mainly works at the network layer. Gateways, also called protocol converters.
Modem: It is a hardware device used to send and receive data over a transmission medium, usually telephone lines. The first modem was introduced in 1960 by AT&T Corporation of the US. AT&T designed its Dataphone, the first commercial modem, specifically for converting digital computer data to analog signals for transmission across its long distance network.