A decentralized, contentious medium access control (MAC) protocol used in Ethernet and other bus-oriented local area networks (LANs). The carrier frequency is sensed by each of multiple stations, or nodes, to determine network availability before accessing the medium to transmit data. Each station must monitor the network to determine if a collision has occurred and the data require retransmission. CSMA variations include Nonpersistent CSMA, 1-Persistent CSMA and P-Persistent CSMA.