COSC 6377 - Computer Networks

Fall 2011

MW 2:30-4:00pm at AH301

InstructorOmprakash Gnawali

Homework - 3

Due: November 16, 2011

Q1: Packets in the Wild

In this question, we will capture some network packets and infer what messages are flowing through the network. We will also give you a sample trace and ask you about the flows captured in that packet trace.

We will use a packet capture tool called Wireshark. Go to Wireshark website at http://www.wireshark.org/ and download Wireshark.

Learn how to capture the packets. Most of the time, we are interested in Promiscuous and monitor mode capture. If you don't set these options, you might not be able to capture all the packets your interface could potentially capture.

Learn how to analyze the packets. Wireshark has a large number of simple to sophisticated analysis tool built-in.

Once you have familiarized yourself with Wireshark, you can start the following part of the assignment:

  1. Capture approx. 30,000 packets any time during 10am - 4pm. How long did it take to capture this number of packets? You will submit this trace along with your homework.
  2. Draw a CDF of packet sizes.
  3. What fraction of packets are 802.11 beacons?
  4. If you were to ignore the 802.11 beacons, what fraction of the remaining packets are TCP/IP and what fraction UDP/IP packets?
  5. What are the most popular websites among the occupants in the building?
We are also making a standard packet capture trace available here. Perform the same analysis as above on this standard trace.

Q2: Home Internet Access Performance

In this question, we will learn how to measure how fast our Internet access is.

We will use a network performance measuring tool called Iperf. Go to Iperf website at http://sourceforge.net/projects/iperf/files/ and download the latest version (2.0.5) of Iperf. Here is a link to a short tutorial on how to use Iperf: http://www.nanog.org/meetings/nanog43/presentations/Dugan_Iperf_N43.pdf

Learn how to use Iperf in Client/Server mode.

You will measure the speed of your Internet access from your home.

  1. What time of the day should you make this measurement?
  2. What are the possible sources of errors in your measurement? Your discussion should include detailed description of the setting and environment in which you made the measurement (service provider, service parameters, make/model of the modem/router, location of the router, where you performed the test, etc.) and your laptop (make/model, CPU, RAM, OS, wireless chipset, driver, etc.). Try to be as complete as possible.
  3. How long should the measurement be?
  4. How many times should you make this measurement?
  5. Should you use TCP or UDP for this measurement?
  6. How did you measure the upload bandwidth vs the download bandwidth?
Use default settings for TCP and UDP traces, except setting the maximum bandwidth for UDP, which you should cap at a very large number, such as 5Gbps. Submit your iperf server and client traces (one second interval), and your conclusions.

Q3: Campus Internet Access Performance

By time you start Q3, we assume you are comfortable using iperf. You also understand the principles behind these measurements. Now, we will try to understand the state of Internet access on campus. We will announce the details of this HW during the class on 10/31. Relevant documents:

Homework Submission

Submit HW through Moodle.