Computer Networking
1st lab Assignment
Instructions:
1) How and when to submit the assignment
 It is mandatory to print pages number 2 and 3 of this document which contains the
questions, and to write the answers by your own handwriting, otherwise the assignment
will be rejected.
 The submission date is going to be Sunday 18th November.
 No assignments will be accepted after the deadline.
2) Required steps before answering the questions
You have to make sure your browser’s cache is empty. (To do this under Firefox, select Tools>Clear Recent History and check the Cache box, or for Internet Explorer, select Tools->Internet
Options->Delete File; these actions will remove cached files from your browser’s cache.)
Now please do the following:
First, Start up your web browser, and make sure your browser’s cache is cleared, as discussed
above, then, start up the Wireshark packet sniffer and enter the following URL into your
browser:
http://gaia.cs.umass.edu/wireshark-labs/HTTP-wireshark-file2.html
Your browser should display a very simple five-line HTML file. After that enter the same URL into
your browser again (or simply select the refresh button on your browser).then stop Wireshark
packet capture, and enter “http” in the display-filter-specification window, so that only captured
HTTP messages will be displayed later in the packet-listing window.
3) How to print a selected packet:
Select the packet you want to print, expand the fields you want to print, then go to File->Print.
Under Packet Range select Selected packet only.
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Answer all questions:
A: Print the first HTTP GET message, its response, the second HTTP GET message and its
response. Please make sure that you have expanded Hyper Text Transfer Protocol field before
printing.
B: Please answer each question in your own handwriting.
1. Compare the status codes for the first and second HTTP GET responses.
Are these similar or not? Why?
(10 marks)
2. Inspect ETag header field in both first and second HTTP GET responses.
What does that field mean? and what does it used for?
(10 marks)
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3. How long did it take from when the HTTP GET message was sent until
the HTTP OK reply was received for the first HTTP GET request?
(10 marks)
4. What is the difference between basic and conditional HTTP GET requests?
How can you identify each type?
(10 marks)
5. What does the field “cache-control: max=0” in the second HTTP GET response
indicate?
(10 marks)
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