In telecommunications and computer networks, a channel access method or multiple access method allows several terminals connected to the same physical medium to transmit over it and to share its capacity. Examples of shared physical media are bus networks, ring networks, hub networks, wireless networks and half-duplex point-to-point links.
Multiple access protocols and control mechanisms are called media access control (MAC), which is provided by the data link protocol layer in the OSI seven layer model as well as in the TCP/IP five layer model.
A multiple access method is based on a multiplex method, that allows several data streams or signals to share the same communication channel or physical media. Multiplexing is provided by the physical layer. Note that multiplexing also may be used in full-duplex point-to-point communication between nodes in a switched network, which should not be considered as multiple access.
Reference:
http://en.wikipedia.org/wiki/Channel_access_method
