CS176A - Introduction to Computer Communication Networks
Homework Assignment #4
Due By December 1st, 2004 at 11:59pm


Assignment Overview

Like HW#3, the goal of this assignment is also to help you understand what is going on in the network by examining exactly what flows across the wire. The traffic file is the same as used in the HW#3. However, the focus of HW#4 is on the Transport and Application layers. You are expected to discover as much high level information as possible.

Assignment Details

The goal of the assignment is to examine real protocols in use and understand the communication that takes place in a network by examining the bits that flow across a network segment. For this assignment, you should focus on the higher level protocols, i.e. pay more attention to the Transport and Application layers.

The instructions for this homework assignment are identical to the instructions for HW#3.  Clearly, you should refer to those instructions to refresh your understanding of the guidelines and requirements.  The one difference is of course the material.  Like HW#3, we have provided a set of questions to help guide you in the direction of the material we expect to be covered in the write-up.  Questions include the following:

  • What high layer protocols are seen at least once somewhere in the trace?
  • What services use TCP, and what services use UDP?
  • What transport-layer port numbers do you see? Do any of them have special significance? Which ones and what is the significance? How are the others chosen?
  • In any of the TCP connections, what is the window size? Does it ever change between connections? How is it chosen?
  • What are the ranges of sequence numbers in each flow?
  • What are the ranges of acknowledgment numbers in each flow?
  • What are the contents and function of each packet (you can summarize series of packets that work to accomplish some high level function but be sure to include a sufficient amount of detail for at least one series of packets)?
  • What host names can be seen in the trace?
  • Can you deduce some host information from the trace? Such as the type and version of the OS, applications and services.
  • Is there some username and password information sent in the clear?
  • Can you guess which commands or applications the tracer launched to generate the traffic?
  • Are there any protocols that appear to be operating differently than as described in class?
  • This packet trace is full of surprises, especially for someone who has never looked at a packet trace in detail before. List a few observations that were surprising to you including details of the observation and why it was particularly noteworthy.

Assignment Turnin

All instructions regarding formatting and submission instructions are the same as for HW#3.  The only differences are the due date and the turnin assignment number.  This assignment is due by December 1st at 11:59pm. Late submissions will not be accepted.  To summarize, the turnin instructions are as follows:

Submit the assignment in HTML format as a single file. Do not forget to include your email, name and Perm#. Your HTML file should be named using the following convention: <firstname-lastname>.html, for example kevin-almeroth.html

To turn in the assignment, use the following command from the Computer Science CSIL lab (if you encounter problems, remote login to csil.cs.ucsb.edu):

csil.cs.ucsb.edu> turnin homework4@cs176a firstname-lastname.html

Points will be taken off if you do not follow the exact procedure given above. If you need help with your submission, contact the TAs.