CPS 214 Written Homework 1 - Fall 1997

Due: Monday, Sept. 15, 5:30 PM

10 points

  1. Use the ping utility to measure the actual RTT between hosts at Duke and other Internet sites. (Read the man page for instructions on how to use the ping utility; on Suns, it is in /usr/etc/ping.) Specifically:

    1. What is the typical RTT between hosts at Duke and others within the Triangle, such as sunsite.unc.edu or eos.ncsu.edu? significantly higher than the RTT between hosts on the same LAN? Warning: explain what you mean by significant! Would most person notice the difference when running interactive applications?

    2. What is a typical RTT between hosts at Duke and others within the south east, such as cs.utk.edu, www.fau.edu or cs.gatech.edu?

    3. What is a typical RTT between hosts at Duke and others on the west coast, such as cs.washington.edu, cs.berkeley.edu or cs.ucsd.edu?

    4. Is the typical RTT between hosts at Duke and sites located in Europe significantly different from the RTT to sites on the west coast? Justify your answer!

  2. Use the utility traceroute to determine which major ISPs (Internet Service Providers Duke uses to reach other sites. (Read the man page for instructions on how to use the traceroute utility; on Suns, it is in /usr/local/bin/traceroute.)

    1. Which ISP does Duke connect to directly? (All travel into and out of Duke travel through this ISP.)

    2. Which ISP does the previously mentioned ISP connect to?

  3. Using ping and traceroute how many hops does a packet typically take across the Internet? Less than 10? Between 10-20? More than 20?

  4. How "wide" is a bit on a 155 Mbps link? Hint: See Peterson, chapter 1. Hint Hint: Be sure you understand the difference between MBps and Mbps.

  5. The latest version of your favorite piece of software was just released but you are at home rather than at school. Although you could ftp the distribution over your modem, you know it will take a long time. Would it be faster to just go to school, knowing that it will take just a few minutes to ftp the software once there? Assume that the distribution is 10MB in size, that you have a 28.8 Kbps modem, and that it would take you about 7 minutes to get to school (if you don't have to stop at each light), and another 7 minutes to get back. Would it be quicker to just download the file using your modem?

  6. Which of the OSI layers handles the following:

    1. Accepting requests from remote machines to print files on a local printer.

    2. Insuring that packets correctly reach the machine at the other end of a communication channel.

    3. End-to-end communication between two hosts separated by a subnet.

    4. Deciding whether to retransmit data that was lost.

    5. Determining which route through the subnet to use.

    6. Insuring that the absence of a light pulse lasting for 1 nanoseconds corresponds to a bit of 0.

    7. Placement of a subroutine library that encrypts data, so that communicating applications protect the data on an end-to-end basis.

  7. For each of the following operations on a remote file server, explain whether they are more likely to be delay sensitive or bandwidth sensitive. Note: You must justify your answer and explain your reasoning (and assumptions) in order to receive full credit.

    1. Open a file (i.e., preparing for the file to be read, but not actually reading any data).

    2. Read the contents of a file.

    3. List the contents of a directory.

    4. Open a file located on the other side of the globe.

  8. What is the principle difference between unicast and multicast communication?