Study of IEEE 802.11 Modified MAC

Abstract: In some recent researches Distributed Coordinate Function becomes an important mechanism in order to access the medium (Channel). The IEEE 802.11 protocol is based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) with a binary exponential backoff (BEB) algorithm to access the channel as the architecture of 802.11 handles MAC(Medium Access Control) layer and specification of Physical layer for Wireless LANs. The backoff procedure reduces the probability of collision enhancing its performance. In binary exponential backoff (BEB) algorithm with every unsuccessful transmission introduces twice the waiting time of a node than the previous value redundant fast-growing retransmission delays for the backlog traffic. Delay in the retransmission can cause the nodes to move out of the collision range in a MANET waiting for retransmission. Hence the growth of waiting time should be reduced in MANET. The number of redundant retransmissions and frequent collisions in BEB reduces the performance of the network. DCF reduces the Contention Window to the original value after every successful transmission which essentially assumes that each successful transmission is an indication that the system is under low traffic loading. QoS (Quality of Service) is a key problem of today’s IP networks.

Keywords: DCF, PCF, IEEE 802.11MAC Layer.