Mac Sublayer

In the IEEE 802 reference model of computer networking, the medium access control or media access control (MAC) layer is the lower sublayer of the data link layer (layer 2) of the seven-layer OSI model. The MAC sublayer provides addressing and channel access control mechanisms that make it possible for several terminals or network nodes to communicate within a multiple access network that incorporates a shared medium, e.g. an Ethernet network. The hardware that implements the MAC is referred to as a media access controller.
The MAC sublayer acts as an interface between the logical link control (LLC) sublayer and the network's physical layer. The MAC layer emulates a full-duplex logical communication channel in a multi-point network. This channel may provide unicast, multicast or broadcast communication service

http://www.ee.surrey.ac.uk/Projects/CAL/networks/Data-Link_Layer.htm

Primary Function Of MAC

•  Addressing of destination stations (both as individual stations and as groups of stations)

•  Conveyance of source-station addressing information

•  Transparent data transfer of LLC PDUs, or of equivalent information in the Ethernet sublayer

•  Protection against errors, generally by means of generating and checking frame check sequence

•  Control of access to the physical transmission medium

• Frame delimiting and recognition