CSG250: Wireless Networks

Spring 2005

Programming Assignment 2: Network throughput and Medium Access Control

Due: Wednesday, March 09 2005

1. Network throughput

The goal of this problem is to study the medium access control approach and its effect on the network throughput. The network has a star topology as illustrated in the following figure. There are 5 CBR sessions going on simultaneously. Nodes 1 to 5 all send packets to Node 0.

Simulation time: 30S

Radio Tx Power: 25 dBm

Packet Size: 512B

As the transmission rate keeps increasing, the congestion at the receiver gets worse, and also the contention at the senders gets tough.

(a) Explain how IEEE 802.11 resolves or alleviates the problem.

(b) Plot the aggregate throughput of the network as a function of traffic rate. Is there an equilibrium point for the aggregate throughput?

2. Network scalability

In this exercise, we study analyze the capacity of ad hoc networks. One can define capacity in different ways -- the maximum data rate that can be achieved overall or the maximum data rate per source, assuming random destinations, or the maximum data rate per source that can be achieved by any traffic pattern, etc.  We are interested in determining how the capacity changes as more nodes are put added to the network. This simulation will help you to understand space reuse, which determines how well the network scales as we expand the network. You may find what are the factors, which factors impact network scalability, and a theoretical analysis in Capacity of Wireless Networks, Mobicom 2001.

Set up a chain network with N nodes. The distance between two neighboring nodes is 100 meters. Node 0 is the source and Node N is the destination. The packets travel along the chain of intermediate nodes towards the destination (a multihop session).

(a) Increasing N from 1 to 8.

Packet length 1500 B.

Tx Power 1dBm

Traffic rate: Adjust your traffic rate to find the maximum throughput for each N.

Change the traffic pattern to N single hop sessions. Let ith node be the CBR Client and (i+1)th node be the CBR server as illustrated in the following figure.

(b) Increasing N from 1 to 8.

Packet length 1500 B.

Tx Power 1dBm/10dBm

Traffic rate: Adjust your traffic rate to find the maximum throughput for each N.

Plot your results in one graph and give a brief analysis of the figures.

3. Hidden Terminal and Exposed Terminal problem.

Set up two scenarios to illustrate the hidden terminal and exposed terminal problem.

(a) Submit your nodes.in, app.conf, config.in.

(b) Explain your settings of transmission power, network topology and traffic pattern and how they create the two problems. Also explain your simulation results, why they imply the existence of the two problems.

The common settings for these three questions are:

No mobility

Static Routing

Propagation Model: Two-Ray

Radio Rx Type: SNR

RADIO-RX-SENSITIVITY -91.0

RADIO-RX-THRESHOLD -81.0

Applications CBR