"CHALLENGES AND REQUIREMENTS OF MAC FOR WSN:The challenges and requirements for mac in wsn are listed as follows:-? Synchronization: If the channel assignment is done dynamically, i.e. the radios are switching betweenchannels instead of being fixed on one channel, a detailed coordination of channel switching isrequired between the senders and receivers in order to be on the same channel at the same time.Scheduled access overcomes this complexity and that is where we benefit from the time-slottedcommunication of single channel LMAC.? Partitions:If transceivers of two nearby nodes are fixed on different frequencies, they cannotcommunicate with each other. MC-LMAC uses a common channel during the control period ofeach timeslot to let the receivers be informed about the requests and about the channels on whichthe data will be sent.? Joining the network:A new node joining the network may disrupt the channel organization or may be requiredto scan all the channels to find the suitable channel to transmit. In MC-LMAC, communicationon a common channel at the beginning of each timeslot lets the new joining node to collect fullinformation about its neighborhood before starting transmission.? Broadcast support:The radio can not switch between the channels immediately but takes some time, forinstance it is around 650¹sec for Nordic Nrf905 radio. The timeslot size in MC-LMAC is largeenough to accommodate the switching time and the overhead of switching time can beconsidered as negligible.? Channel switching:9 The radio can not switch between the channels immediately but takes some time, forinstance it is around 650¹sec for Nordic Nrf905 radio. The timeslot size in MC-LMAC is largeenough to accommodate the switching time and the overhead of switching time can beconsidered as negligible., 10 WHY MAC FOR WSN?Maximizing the network lifetime is a common objective of sensor network research, since sensornodes are assumed to be dead when they are out of battery. Under these circumstances, theproposed MAC protocol must be energy efficient by reducing the potential energy wastespresented below. The types of communication patterns that are observed in sensor networkapplications should be investigated, since these patterns determine the behavior of the sensornetwork traffic that has to be handled by a given MAC protocol.Reasons of energy waste:? Collision:When a node receives more than one packet at the same time, these packets are termedcollided, even when they coincide only partially. All packets that cause the collision have to bediscarded and retransmissions of these packets are required, which increase the energyconsumption. Although some packets could be recovered by a capture effect, a number ofrequirements have to be achieved for successful recovery.? Overhearing:The second reason for energy waste is overhearing, meaning that a node receives packetsthat are destined to other nodes.? Control packet overhead:The third energy waste occurs as a result of control-packet overhead. A minimal numberof control packets should be used to make a data transmission. One of the major sources ofenergy waste is idle listening, that is, listening to an idle channel in order to receive possibletraffic.? Overmitting:The last reason for energy waste is overemitting, which is caused by the transmission of amessage when the destination node is not ready.11 "