Homework #2

(30 points total)

Description

(This problem continues from problem 2 of HW1.) Use NS-2 to set up the following topology,

where,

• There are 6 nodes as shown in the figure above.
• The link annotations are bandwidths and delays.
• All queues are DropTail queues. The queue limit for the link between nodes 2 and 3 is 8 packets.
• There is a TCP flow from node 1 to node 5 carrying an FTP connection. This flow starts at 0.1 seconds and ends at 3.0 seconds.
• There is a UDP flow from node 0 to node 4 carrying CBR traffic which starts at 1.0 seconds and ends at 2.0 seconds.
• The entire simulation terminates at 3.0 seconds.

Requirements

1. Write an NS-2 tcl script based on the template given below.
2. Trace the TCP congestion window size in your script.
3. Use Xgraph to plot the TCP congestion window fluctuations as a function of time. [BC: Added 3/16/2007] On nunki.usc.edu, please do not use /usr/usc/X/bin/xgraph but use ~csci551b/bin/xgraph instead. [BC: Added 3/28/2007] The TA has written some notes about the xgraph file format
4. Write a brief analysis based on what you see in the plot. In your analysis you must address the following: what happened during which intervals or at which times and what feature(s) does this TCP lack?
5. See the submission section below regarding what you need to submit.

Template

To write your ns-2 script, you can start with hw1-2.tmpl.txt, a template provided for your in HW1, and fill in your own code.

• hw2.tcl - your ns-2 script for problem 1, based on hw1-2.tmpl.txt from HW1.
• hw2.README - your answer to the question posed in problem 1.

You can create your submission by doing the following:

    % tar cvf hw2.tar hw2.tcl hw2.README*
    % gzip hw2.tar
    % ~csci551b/bin/bsubmit upload \
          -event  \
          -file hw2.tar.gz