The Media Access Control Layer is one of two sublayers that make up the Data Link Layer of the OSI model. The MAC layer is responsible for moving data packets to and from one Network Interface Card (NIC) to another across a shared channel.
See a breakdown of the seven OSI layers in the Quick Reference section of Webopedia.
The MAC sublayer uses MAC protocols to ensure that signals sent from different stations across the same channel don't collide.
Different protocols are used for different shared networks, such as Ethernets, Token Rings, Token Buses, and WANs.
Also see "The OSI Reference Model — Understanding Layers" in Webopedia's "Did You Know..." section.
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