The media access control (MAC) is a data communication protocol and it is a sub-layer of the data link layer. It allows several nodes in the network to share the medium using the channel access control mechanisms. Collision in MAC layer is the major issue in wireless transmissions. Generally, two-way handshaking and four-way handshaking mechanism reduces the collision rate. In the two-way handshaking signal strategy, a node transmits the acknowledgement to the sender node on receiving the data packet. In the four-way handshaking signal strategy, the optimized MAC protocol uses Ready to Send/Clear to Send (RTS/CTS) technique to reduce the packet collision in wireless transmissions. The back-off algorithms also play a vital role in reducing the collision between nodes, especially if more than one node attempts to send data on the channel simultaneously. Improving the functionality of the back-off algorithms to estimate the optimal back-off waiting period is still a major issue. The MAC layer offers two classes of services, namely Distributed Coordination Function (DCF) and Point Coordination Function (PCF).
Solution in NS2
i) In NS2, the IEEE 802.11 MAC standard is applied to the network and the performance is evaluated.
ii) Four way handshaking is the default mechanism available in ns2.
iii) Performance under Two way handshaking mechanisms can be evaluated by disabling the RTS/CTS settings.
iv) Back off algorithm can be tested by varying inbuilt back-off variable and contention window size.
v) Channel access delay minimization and throughput increment can be illustrated using x-graph.
vi) Performance metrics such as frame overhead, contention overhead, delay, packet delivery ratio, dropped packets due to collision, throughput and energy consumption can be analyzed by processing the trace file using awk script.
For Further Details Visit : http://slogix.in/