A printed circuit board that provides a transmitting/receiving port for a local area network (LAN) or a carrier's telephone or wide area network (WAN). Line cards plug into telephone company switches and high-end routers, which have a modular chassis that accepts a range of cards.
Small and medium-size routers have a fixed number of ports, typically Ethernet, and the line card circuitry is built into each port. In a user's desktop or laptop computer, the counterpart of the line card is a circuit on the motherboard or a plug-in network card (see
network adapter).