The Media Access Control (MAC) data communication protocol sub-layer, also known as the Medium Access Control, is a part of the data link layer specified in the seven-layer OSI model (layer 2). It provides addressing and channel access control mechanisms that make it possible for several terminals or network nodes to communicate within a multipoint network, typically a local area network (LAN) or metropolitan area network (MAN). A MAC protocol is not required in full-duplex point-to-point communication. In single channel point-to-point communications full-duplex can be emulated. This emulation can be considered a MAC layer.
The MAC sub-layer acts as an interface between the Logical Link Control sublayer and the network's physical layer.
The MAC layer provides an addressing mechanism called physical address or MAC address. This is a unique serial number assigned to each network adapter, making it possible to deliver data packets to a destination within a subnetwork, i.e. a physical network without routers, for example an Ethernet network.
Media access control is often used as a synonym to multiple access protocol, since the MAC sublayer provides the protocol and control mechanisms that are required for a certain channel access method. This makes it possible for several stations connected to the same physical medium to share it. Examples of shared physical medium are bus networks, ring networks, hub networks, wireless networks and half-duplex point-to-point links.
Examples of packet mode multiple access protocols for wired multi-drop networks are:
- CSMA/CD (used in Ethernet and IEEE 802.3),
- Token bus (IEEE 802.4)
- Token ring (IEEE 802.5)
- Token passing (used in FDDI).
Examples of multiple access protocols that may be used in packet radio wireless networks are:
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