Network Interface Cards (NIC), also known as Network Interface Units (NIU) are chipsets on printed circuit boards that provide physical access from the node to the LAN medium. The NIC is responsible for fragmenting the data transmission and formatting the data packets with the necessary header and trailer. A standard IEEE NIC contains a unique, hard-coded logical address (MAC address), which it includes in the header of each data packet it transmits. The NIC typically has some amount of buffer memory, which enables it to absorb some number of bits transmitted by the associated device, form the packets, and hold them until such time as the network is available.
In the context of the OSI Reference Model, NICs function at the Physical and Data Link layers. The NIC also may contain a microprocessor that can relieve the attached device of some routine computational functions.
The NIC can take a number of forms, including a circuit board that fits into the expansion slot of a desktop PC, a PCMCIA card, or a stand-alone device. Transceivers (transmitter/receivers) are used in LANs to receive a carrier signal and then transmit it on its way. They are embedded in NICs.
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| Figure 9: Fast Ethernet NIC |
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