CNT 4704: Computer Communication Networks

Fall 2008

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Homework 1

(assigned 09/30; due: 10/09, submitted in class by hard-copy)

1.  Chapter 1, Problem 7. You can leave you answer in terms of an expression (e.g., with sums) to be evaluated (i.e., you need not provide a specific numerical value). 

2. Perform "traceroute" from your computer at home to www.google.com at three different hours of the day (in windows, use tracert).

    a). Copy the three times traceroute report in your homework report.

    b). Find the number of routers in the path at each of the three hours. Did the paths change during any of the hours? Did the traceroute go to different IP addresses of www.google.com?

    c). Try to identify the regions or ISP networks that the traceroute packets pass through from the source to the destination. 

3.  Chapter 2, problem 1.  If a statement is false, explain briefly why it is wrong.

4.  Chapter 2, problem 4.

5. Chapter 2, problem 5.

6. Suppose you open a startup company "flashNetwork" and want to set up your company network. Your network has the following servers:

1. DNS server: "dns.flashNetwork.com" with IP as "128.119.12.40"
2. Web server:  "flashNetwork.com" with two IP as "128.119.12.55" and "128.119.12.56". Internet users can also access the web server by "www.flashNetwork.com".
3. Email server: "mail.flashNetwork.com" with IP as "128.119.12.60"

Your company's email address is "username@flashNetwork.com".

a). What resource records (RRs) do you need to provide to the upper-level ".com" Registrar?

b). What RRs do you need to put in your company's DNS server?

7. Consider the networks shown in the figure below. Assume computers in the institution send out 13 requests per second. Each object average size is 100,000 bits. Also assume the internet side delay of a request is 1 seconds. Using M/M/1 queue to model the access delay in the 1.5Mbps access link. That is to say, the average delay time for an object on the access link is E[T] = 1/(x-y), where y is the arrival rate of objects to the access link and x is the service rate of the access link (i.e., on average, the access link could server x objects per second).

a).  Find the total average response time when no institutional cache is used. (Hint: total delay includes Internet delay, access link delay, and LAN delay)

b).  Now suppose the institutional cache is used. The hit rate for the cache is 0.6.  Find the total average response time.