Abstract: Nowadays the ocean plays an increasingly important role in the development of human society. As a basilic means to learn about the sea, underwater communication technology becomes a popular nodus in research. Different from the terrestrial wireless communication in channel characteristics and performance requirements, conventional wireless communication MAC(medium access control) does not apply to it, MAC protocols for various underwater acoustic applications were continuously proposed. After outlining the characteristics of underwater acoustic sensor network and the designing standards of MAC, current control mode was divided into contention-based protocol and scheduling-based protocol according to the pattern by which the channel was accessed. The contention-based protocols were further divided into random access and collision avoidance according to their modes of dealing with collision, while scheduling-based ones into dynamic allocation and static allocation according to dynamics of channel allocation. Under this classification,the design idea and primary mechanism of current main protocols were described, their performance differences werediscussed such as energy efficiency, channel utilization and throughput, and a new development direction was presented for the improvement of the MAC protocols.

Key words: Propagation Underwater acoustic sensor network, Scheduling-based MAC protocol, Contention-based MAC protocol,delay, Collision avoidance, Energy efficiency