NS Lab

            By: Nicholas Borelli & Hong Kin Pun

                                        (code provided by Soma Ghosh and Marc Greis)

Wireless LANS (IEEE 802.11) Network Simulator

IEEE 802.11 wireless networks are gaining popularity and being used more and more in everyday businesses, schools, and homes.  These LANS are easy to set up and very cost effective. However, problems, such as hidden and masked nodes, are apparent in these networks and cause packet collisions.

Introduction

Tutorials:

Tutorial 1

Creating a Wireless Network

Tutorial 2

The Hidden Node Problem

Tutorial 3

The Masked Node Problem

 

Questions and Analysis

  1. What is the trace file used for and what is most useful about the file that you can get from it? (hint: read introduction).
  2. Why do packets starts getting dropped as nodes move away in a wireless network?
  3. What is the persistent of the CSMA protocol used for wireless networks? Why?
  4. How does RTS/CTS solve the problem of hidden nodes?
  5. Why doesn't RTS/CTS solve the problem of masked nodes?
  6. Print out the plot of the data rate at the sink for the hidden node network (if not familiar to how this is done, refer to this link ... Getting Results You Can Use and More Results You Can Use).
  7. Double the packet size.  What happens to the data rate to each variation? Check with the simulation and use the plot from Question 6 to compare with the plots of these two.  Also check with the trace file and explain the differences between these changes.  Repeat with the packet size reduced by half.
  8. Do the same as Question 7 for the packet sending rate.
  9. Now repeat the Questions 6-8 for the masked node network.