A network interface unit (NIU) (sometimes called a network interface device) is a device that serves as a common interface for various other devices within a local area network (LAN), or as an interface to allow networked computers to connect to an outside network. The NIU enables communication between devices that use different protocols by supplying a common transmission protocol, which may be used instead of the devices' own protocols, or may be used to convert the specific device protocol to the common one. To enable an interface between a LAN and another network, the NIU converts protocols and associated code and acts as a buffer between the connected hardware. A network interface card (NIC) is a type of NIU.
Dig Deeper on LANs (Local Area Networks)