CSMA (Carrier Sense Multiple Access) is a Media Access Control (MAC) protocol that is used to control the flow of data in a transmission media so that packets do not get lost and data integrity is maintained.There are two modifications to CSMA:1) CSMA CD (Collision Detection)2) CSMA CA (Collision Avoidance) IEEE 802.11 wireless LANs us a media access control protocol called Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA).Unlike CSMA/CD (Carrier Sense Multiple Access/Collision Detect) which deals with transmissions after a collision has occurred, CSMA/CA acts to prevent collisions before they happen.In CSMA/CA, as soon as a node receives a packet that is to be sent, it checks to be sure the channel is clear, i.e. no other node is transmitting at the time). If the channel is clear, then the packet is sent. If not, the node waits for a randomly chosen period of time and then checks again to see if the channel is clear.