Applications

  1. Kurose & Ross, Chapter 2, Problem P10.

    Consider a short, 10-meter link, over which a sender can transmit at a rate of 150 bps in both directions. Suppose that packets containing data are 100,000 bits long, and packets containing only control (e.g. ACK or handshaking) are 200 bits long. Assume that N parallel connections each get $1/N$ of the link bandwidth. Now consider the HTTP protocol, and suppose that each downloaded object is 100 Kbits long, and that the initial downloaded object references 10 additional objects from the same sender.

    a. Would parallel downloads via parallel instances of non-persistent HTTP make sense in this case?

    b. Now consider persistent HTTP. Do you expect significant gains over the non-persistent case? Justify and explain your answer.

  2. Kurose & Ross, Chapter 2, Problem P11.

    Consider the scenario introduced in the previous problem. Now suppose that the link is shared by Bob with four other users. Bob uses parallel instances of non-persistent HTTP, and the other four users use non-persistent HTTP without parallel downloads.

    a. Do Bob's parallel connections help him get Web pages more quickly? Why or why not?

    b. If all five users open five parallel instances of non-persistent HTTP, then would Bob's parallel connections still be beneficial? Why or why not?

  3. Kurose & Ross, Chapter 2, Problem P21.

    Suppose that your department has a local DNS server for all computers in the department. You are an ordinary user. Can you determine if an external web site was likely accessed from a computer in your department a couple of seconds ago? Explain.

  4. Kurose & Ross, Chapter 2, Problem P26.

    Suppose Bob joins a BitTorrent torrent, but he does not want to upload any data to other peers (so-called free-riding).

    a. Bob claims that he can receive a complete copy of the file that is shared by the swarm. Is Bob's claim possible? Why or why not?

    b. Bob further claims that he can make his free-riding more efficient by using a collection of multiple computers (with distinct IP addresses) in the computer lab in his department. How can he do that?

  5. Kurose & Ross, Chapter 2, Problem P27.

    In the circular DHT example in Section 2.6.2, suppose that peer 3 learns that peer 5 has left. How does peer 3 update its successor state information? Which peer is now its first successor? Its second successor?

  6. Kurose & Ross, Chapter 2, Problem P28.

    In the circular DHT example in section 2.6.2, suppose that a new peer 6 wants to join the DHT and peer 6 initially only knows peer 15's IP address. What steps are taken?

  7. Read the article titled The Economics of Spam by Justin M. Rao and David H. Reiley, published in The Journal of Economic Perspectives in 2012. You can obtain this article for free if you are logged in on the BYU campus. Write a short (2-3 paragraph) summary of the article that explains its major points. Then write a paragraph explaining and justifying your preferred solution to the problem of spam.

  8. BitTorrent uses incentives to encourage users to share the portions of a file they have downloaded already. What problem could this cause for a user who starts out without any of the file? How could you solve this problem without removing incentives entirely? Would your solution make it easier for free-loaders to download the file without ever sharing anything?