Assignment

• Select two systems in the lab (or at home on the same LAN) make sure that they you are able to pass messages between them

• Establish Wireshark on one of the systems and be sure that you can see all the messages coming and going

• Start the collector on Wireshark

• Send a very large file (greater than 5 M) from one system to the other (you may send one in each direction to get the full effect)

• Collect all the information in Wireshark regarding the file transfer

• Stop the collector and save the file at the end of the experiment

• Answer the following questions in a paper (please include Wireshark screenshots to support your discussion):

1. Show the three way handshake at the start of the exchange (you may need to restart the transfer to catch this). What flags are set for each portion of the handshake? What other fields are involved (how does the message format change?)

2. What is the effect of the WINDOW field? What is it used for? How big is it? Why is it that size?

3. How does the ack/nak process work? Draw a diagram of the sending and ack for what got sent. Make sure to find some screen shots to back this up.

4. Do you need to ack each message before another can be sent? How many messages can be outstanding (not acked at any one lime?) Did you see this in your experiment?

5. How does the system conclude the transfer? How does it end the TCP session?

6. Does TCP seem to play an important role in Distributed Systems design? Why is it useful? Can you think of a scenario where you might not want the features of TCP? why?