This exam is open-book, open-notes, open-computer, open-Internet, but closed-other-people. You may, however, ask Jeff Ondich questions. In particular, you should feel free to ask to use reference materials he may have in his office.

This exam is part normal exam and part scavenger hunt. Some of the questions are easy to answer if you have a pen and a piece of paper, while others will require you to do some research, probably of the Web browsing variety. Answer the questions as completely and clearly as you can. Have fun.

1. Suppose you want to use the UNIX command telnet as an FTP client, and your goal is to retrieve a file called gobackn.c from the directory ~/jondich in the account networks on turing.mathcs.carleton.edu. What UNIX command (including command-line arguments) will you execute? Once connected to turing's FTP server, what do you need to type to retrieve the file in question?
2. What is RSA 129? In whose column was it introduced? Who solved it, when, and how? What are the magic words, and what do they mean?
3. Suppose N is the 129-digit product of a 65-digit prime and a 64-digit prime. If you try to factor this number by computing N mod k for each odd number k starting with 3 and stopping when N mod k = 0, how long will it take? Pretend that your computer can compute N mod k for a billion different values of k each second.
4. In what contexts is Manchester encoding used? Why is it used instead of a high voltage for 1 and a low voltage for 0?
5. If you want to make your Hayes-compatible modem answer the phone on the fourth ring, what command would you send it? What's the largest number of rings you could make the modem wait before answering?
6. In the context of data link protocols, we have seen at least two definitions of "efficiency." Give two definitions of efficiency.
7. Suppose two hosts on an 802.3 network are trying to transmit. Their first attempt results in a collision. If no other hosts try to transmit, what is the probability that the two hosts in question will collide at least two more times?
8. If you are sending this exam (an ASCII HTML file) over a network that uses the bit stuffing scheme described on page 181 of Tanenbaum, are there characters or combinations of characters that would require bit stuffing? Explain.
9. If you search for the string "pr-01" in the RFC index, you will find some pretty interesting documents. Why? What's your favorite RFC you found this way?
10. Concerning the Go-Back-N algorithm on pages 210-211 of Tanenbaum.
    • Suppose you eliminated all timer-related code instructions from Tanenbaum's code. Under what circumstances could the resulting code reach deadlock (that is, a condition where both sender and receiver are waiting for events that can't occur).
    • Even if you don't modify Tanenbaum's code, there's a way to reach a form of deadlock. What is it?
    • Last week, I told several of you that you could implement Tanenbaum's code using just one timer instead of one timer per entry in the sender's window. Suppose you used a single timer, and reset it every time you sent a frame. Would the resulting protocol work? How would it differ in performance from the one-timer-per-window-entry version?