  The challenge of designing an efficient Medium Access Control (MAC) protocol
and analyzing it has been an important research topic for over 30 years. This
paper focuses on the performance analysis (through simulation) and modification
of a well known MAC protocol CSMA/CD. The existing protocol does not consider
the wastage of bandwidth due to unutilized periods of the channel. By
considering this fact, performance of MAC protocol can be enhanced. The purpose
of this work is to modify the existing protocol by enabling it to adapt
according to state of the network. The modified protocol takes appropriate
action whenever unutilized periods detected. In this way, to increase the
effective bandwidth utilization and determine how it behaves under increasing
load, and varying packet sizes. It will also include effects of attacks i.e.
Denial of service attacks, Replay Attack, Continuous Channel Access or
Exhaustion attack, Flooding attack, Jamming (Radio interference) attack,
Selective forwarding attack which degrade performance of MAC protocol. In
Continuous Channel Access or Exhaustion attack, a malicious node disrupts the
MAC protocol, by continuously requesting or transmitting over the channel. This
eventually leads a starvation for other nodes in the network w.r.t channel
access. remedy may be the network ignores excessive requests without sending
expensive radio transmissions. This limit however cannot drop below the
expected maximum data rate the network has to support. This limit is usually
coded into the protocol during the design phase and requires additional logic
also. Repeated application of these exhaustion or collision based MAC layer
attacks can lead into unfairness.
