Lab c2: 802.11 Fairness and Comparison of DSR and AODV Routing Protocols

PART I - Comparison of DSR and AODV Routing Protocols


This assignment aims at making the students familiar with the reactive (on-demand) routing protocols used in ad hoc networks and compare the performance of DSR and AODV protocols.

Performance Metrics used

We will evaluate the routing protocols in terms of two metrics-
1. Packet Delivery Fraction/Ratio : It is the ratio of packets delivered to that transmitted by the source.
2. Routing Load : It is the number of routing packets sent per data packet delivered.

NS2 Instructions

Hand In (Part I)

1. Plot each performance metric for both DSR and AODV versus pause-times, for each CBR Load.
2. State if any peculiar behavior is observed. Give a brief report as to the interpretation of the graphs.
3. Write briefly about what you understand by the random node movement files (generated by ./setdest command in the script file) and traffic pattern files (generated by ns cbrgen.tcl command in the file) and their usage in this assignment.


1. You will need to use the trace files calculation in many ns2 simulations. Hence, it is good idea to get familiar with the trace file formats. Go through the sections 16.1.6 and 16.1.7 of the ns2 manual. Can you now make out the use of grep commands provided in this assignment?
2. If time permits, try running the whole experiment with seed = 2 in the and, in the "ns cbrgen.tcl..." command. And make the plots again. Does the behavior change markedly?
3. Study about the cmu-gen utilities we have used in this assignment (used in the and files).

PART 2 - 802.11 Fairness


The goal of this exercise is to understand the concept of starvation and unfairness in IEEE 802.11 standard.

We consider the following topology:

There are 2 CBR flows: f1 (N0->N1) and f2 (N2->N3) that start at the same time.

NS2 Instructions

Hand In (Part II)

Turn in plots from the previous section. Expected plots are the per flow throughput vs distance x for different x values. Also, turn in your answers to the questions in the analysis section.


This assignment lets you understand how unfairness can play its role in 802.11. Looking at the results, you will realize that there is lot happening behind this simple looking topology. First try to recall the following about 802.11 and ns2 , then try to answer latter questions with respect to the graph obtained above-
1. If a node correctly decoded the last packet detected, it must sense the channel to be idle for DIFS prior to resuming backoff. If it detected a packet but couldn't correctly decode it, it must backoff for EIFS. EIFS > DIFS.
2. If a node sends an RTS and does not receive a CTS, it doubles its contention window and then retries.
3. As per default ns2 settings, TX Range is approx. 250m and CS Range approx. 550m. This simply means that nodes within TX Range can detect as well as decode the packet correctly but nodes outside TX Range but within CS Range are only able to detect the packet. This further implies that such nodes(outside TX Range) would back off for EIFS and not DIFS.
Keep these in mind and answer the following:

1.What do you observe from the graph obtained? Can you explain the observations on the basis of the 802.11 contention resolution/backoff mechanism?
2.There are different types of "fairness", please explain the difference between short-term and long-term fairness. Which type is harder to achieve?


1. Overview of IEEE 802.11
2. Know ns2