“Media Access Control (MAC) is the lower sub-layer of the OSI data link layer, the interface between a node’s Logical Link Control and the network’s physical layer. The MAC differs for the various physical media (such as Ethernet, token ring, WLAN). The MAC sub-layer is primarily concerned with: 1) recognizing where frames begin and end in the bit-stream received from the physical layer (when receiving), 2) delimiting the frames (when sending), inserting information (e.g. some extra bits) into or among the frames being sent so that the receiver(s) are able to recognize the beginning and end of the frames, 3) detecting transmission errors by means of inserting a checksum into every frame sent, recalculating, and comparing them on the receiver side, 4) inserting the source and destination MAC addresses into every frame transmitted, 5) filtering out the frames intended for the station by verifying the destination address in the received frames, 6) controlling access to the physical transmission medium (which of the stations attached to the wire or frequency range has the right to transmit)”