"INDEX ? Introduction ? Definition ? Architecture of wsn ? Challenges and requirements of mac for wsn ? Why mac for wsnPairwise ? Types of mac ? Mac protocols for wsn ? Conclusion ? ReferencesIntroduction ? pairwise=pair of channels. ? Time hopping=using time slots for transmisionof data. ? Mac=medium access control protcol for ? Wsn=wireless sensor network. ? pairwise+time hopping + mac + wsn= pairwise:atime hopping medium access control protocol forwireless sensor networks.Definition ? Pairwise: PairWise, is a novel, low power, time division multiple access (TDMA) based protocol for use in WSNs. ? Wsn: A wireless sensor network consists of a large number of tiny sensor nodes, each of which is equipped with a radio transceiver, a small microprocessor and a number of sensors. ? Mac for wsn: Maximizing the network lifetime is a common objective of sensor network research, since sensor nodes are assumed to be dead when they are out of battery. Under these circumstances, the proposed MAC protocol must be energy efficient by reducing the potential energy wastesArchitecture OF WSN ? ARCHITECTURE OFWSN CONSISIT OF FOUR PARTS:- ? ENERGY SOURCE ? SENSING BLOCK ? PROCESSING BLOCK ? COMMUNICATION BLOCKCHALLENGES AND REQUIREMENTSOF MAC FOR WSN ? Synchronization ? Partitions ? Joining the network ? Broadcast support ? Channel switching WHY MAC FOR WSN? ? Reasons of energy waste: ? Collision ? Overhearing ? Control packet overhead ? Idle listening ? overmittingPAIRWISE ? Neighbor Discovery? Channel establishment ? Broadcast support ? Time synchronizationTYPES AND CATAGORIES OF MAC ? TYPES ? CATAGORIES ? CONTENSION BASED? SOLITARY PROTOCOLS PROTOCOLS ? CROSSLAYER? SCHEDULED BASEDPROTOCOLS PROTOCOLS ? HYBRID BASEDPROTOCOLS"