Medium Access Control (MAC) makes it possible for multiple users to access the same communication resource simultaneously. It is part of the data link layer that is the layer just above the PHY layer (see Chap. 6 for detailed layered protocol models), typically categorized as an essential part of the radio interface covering the lowest layers of the network, as shown in the previous chapters. It provides the abstraction of the PHY layer for upper layers, resolves the addressing of source stations and the destination stations via MAC address, determines channel access methods for transmission and performs multiple access resolutions when more than one data frame is to be transmitted simultaneously. MAC addresses can be hard coded in network interface controllers (NICs) or generated for each session. The MAC layer encapsulates the frames into a suitable format that can be transmitted by the radio interface over the wireless channel.