The Media Access Control (MAC) sublayer is the part of the OSI network model data link layer that determines who is allowed to access the physical media at any one time. It acts as an interface between the Logical Link Control sublayer and the network's physical layer.

The MAC sublayer is primarily concerned with the control of access to the physical transmission medium (i.e. which of the stations attached to the wire or frequency range has the right to transmit?) or low-level media-sharing protocols like CSMA/CD.

The upper Data-Link sub-layer, the Logical Link Control (LLC) sub-layer takes care of:

• recognizing where frames begin and end in the bit-stream received from the physical layer (when receiving)
• delimiting the frames (when sending), i.e. 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
• detection of transmission errors by means of e.g. inserting a checksum into every frame sent and recalculating and comparing them on the receiver side IEEE Std 802®-2001, IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture, section 6.2.3 MAC sublayer
• inserting the source and destination MAC addresses into every frame transmitted
• filtering out the frames intended for the station by verifying the destination address in the received frames

See also

• MAC address
• Ethernet
• token ring

References