Network Simulations

References http://www.isi.edu/nsnam/ns/tutorial/index.html

1. Read Section V: Making it more interesting on http://www.isi.edu/nsnam/ns/tutorial/index.html.

Download example2.tcl and use the ns simulator to answer the following questions.

(a) (5 marks) Reduce the bandwidth on the link between node 1 and node 2 to 0.5Mbps. Describe what happens in the simulation and how this compares with the original example2.tcl simulation.

(b) (5 marks) Increase the bandwidth on the link between node 1 and node 2 to 10Mbps and configure the traffic source at node 1 such that packets will be sent every 0.0005 seconds. Describe what now happens in the simulation.

(c) (5 marks) In your network in question 1b, what is the minimum bandwidth required on the link between node 2 and node 3 such that no packets are dropped at node 2?

(d) (5 marks) The original example2.tcl uses a stochastic fair queue (SFQ) on node 2. In the original example2.tcl, change the queue on node 2 to be a DropTail queue and describe how the SFQ queue compares with the DropTail queue.

(e) (5 marks) In your example2.tcl file in question 1d, add the following line: $ns queue-limit $n2 $n3 5 after the line $ns duplex-link-op $n2 $n3 queuePos 0.5 to set the maximum size of the DropTail queue on node 2 to be 5 packets. Run the simulation. Then set the maximum size of the DropTail queue on node 2 to be 20 packets and re-run the simulation. How does a queue limit of 5 2 packets compare with a queue limit of 20 packets? 2. Read Section VI: Network Dynamics on http://www.isi.edu/nsnam/