CSG250: Wireless Networks

Spring 2005

Programming Assignment 2: Network throughput and Medium Access Control

Due: Wednesday, Mar 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 IEEE802.11 resolves or alleviates the problem.

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

2. Network scalability

The capacity of wireless networks is always a big concern. Is it true that the capacity will keep increasing when more nodes are put into the area? This simulation will help you to understand the space reuse, which determines how well the network scales. You may find what are the factors, which impact the network scalability, and an 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