Web page 2 of three
Query 2- Contemplate a Broadcast 802.11 community that follows CSMA/CA protocol. In broadcast mode,
every node sends a packet following CSMA/CA guidelines and enters backoff if it nonetheless has packets to ship.
Assume that a new packet arrival additionally causes the node to enter the backoff process even if there was
no different packet in the queue. If the backoff counter is thought-about a Markovian stochastic course of, the
following Markov Chain describes this course of. Every state represents the worth of the backoff counter at
the starting of an idle slot (for numbered states), whereas state a represents a case the place the backoff
counter has no worth and is ready for a new packet arrival earlier than it begins the random backoff
process. Pa is the chance of a new message arrival.
Reply the following questions:
Half 1 (25pt)
a) Clarify what W is.
b) Specific all transition chances (assume Pa and W are identified).
c) Clear up the mannequin and derive bi, the stationary distribution of the chain as a perform of W and Pa.
Half 2) (25pt)
d) Assume that packet arrival is such that every node at all times has a packet to ship (i.e., after each
packet transmission, there is no want to wait for a new packet to begin rivalry for the
channel). This is the saturation mode. Simplify the above Markov chain for such a community. Draw
the new MC.
e) Specific the transition chances
f) Clear up the mannequin to derive bi
Half three) (25pt)
g) Take the MC from half 2, assume that after a transmission a random backoff quantity is chosen
in accordance to a new rule as follows: the random quantity is chosen between 2 and W+5 (with
uniform distribution as earlier than). Backoff additionally occurs as regular (rely down after seeing an idle
slot). Draw a new Markov Chain that describes such a backoff course of.
h) Specific the transition chances (no want to remedy the mannequin).
Trace : See the following two papers; they have all the info you might want to remedy the above
Web page three of three
 G.Bianchi,“Efficiency Evaluation of the IEEE 802.11 Distributed Coordination Perform,” IEEE J. Chosen
Areas Communications, vol.18, no.three, pp.535-547,Mar.2000.
 Yaser P. Fallah, CL Huang, R. Sengupta, H. Krishnan, “Evaluation of Data Dissemination in Vehicular
Advert-Hoc Networks with Utility to Cooperative Car Security Methods”, IEEE Trans. on Vehicular
Expertise, Vol 60, Difficulty 1, pp. 233-247, Jan 2011