Wireless Networking Lab 105: Data Throughput

Introduction

This simulation exercise explores the impact of MAC overhead and multiple hops on achievable data throughput in a wireless network.

We'll separately analyse the impact of MAC overhead using single hop topology and impact of multiple hops on the attainable throughput.


Fig 1: The simulation set-up comprises two nodes S and D in direct range of each other. S acts as a CBR source, with D being the sink.

Fig 2: The simulation set-up comprises a linear chain of nodes S-I1-I2...Im-D, where consecutive nodes are placed at a distance of 200m from each other. S acts as a CBR source, with D being the sink. We shall assume a data-rate of 11.0 Mbps, and vary the length of the chain.

ns2 Instructions

Part (a): Impact of MAC Overhead

1. Get the tcl script from here.
2. A script "single-hop.tcl" is provided. This script takes as a command-line argument the transmission rate (in bps). Script usage is : ns single-hop.tcl -drate {data-rate}
3. You are required to run simulations for data rate values 1.0e6, 2.0e6, 5.5e6 and 11.0e6.
4. Determine the achieved data throughput (in Mbps) for each. Plot a graph of (throughput/data-rate) vs. data-rate. (To calculate throughput, you need to calculate [num of received packets/num of sent packets]. Go through the sections 16.1.6 and 16.1.7 of the ns2 manual for understanding and using trace files. For this particular assignment, use the commands 'grep "^s" {trace file name} | wc -l' and 'grep "^r" {trace file name} | wc -l' to get the number of sent and received packets respectively.)
5. How does (throughput/data-rate) vary with changing datarate? Explain briefly the trends you observe, as well as any reasons for those trends.

Part (b): Impact of multiple intervening hops between Source and Destination

1. Get the tcl script from here.
2. A script "multi-hop.tcl" is provided. This script takes as a command-line argument the total no. of nodes i.e. if you provide "k" as the argument, you shall have (k-1) hops between S and D. Script usage is : ns multi-hop.tcl -nn {numnodes}
3. Run simulations for k=2, 3, 4, 5, 6.
4. Plot the achieved end-to-end CBR throughput vs. the number of hops.
5. Explain briefly the trends you observe, as well as any reason for those trends.

References

1. Overview of IEEE 802.11
2. Know ns2