CS176A - Introduction to Computer Communication Networks
Homework Assignment #3
Due BEFORE (2:00pm) Class on Thursday, November 13th, 2003

Assignment Overview

Some of the questions in this assignment are basic, while others will require some extra thinking and/or searching (in the book or using Google) so that you could build on the basics that you know.


Use as much space as needed to answer the following questions. If you use Google search engine, list the URL's used.


1.      When would ALOHA do better (in terms of throughput) than Slotted ALOHA? And when would the opposite be true? (6 points)


2.      Briefly mention the difference between Link State routing and Distance Vector routing. Give an example of a protocol for each type of routing. (6 points)


3.      What is CIDR? Why did a need arise for it (Give a scenario that would clarify this need)? (8 points)


4.      What is DHCP? When would it be a good idea to use it? And when would it be a bad idea? (8 points)


5.      Give a scenario where you would need to use a DHCP server and a NAT box at home. In other words, when would you need both of them at your home? (8 points)


6.      We know the function of the “Type” field in the Ethernet header, which field in the IP header has a similar function? What is the function of these fields in IP and the Data Link layers? (6 points)


7.      Run the simulation applet on the web page: http://www.rad.com/networks/1998/packet/sim.htm. Run both the virtual circuit and datagram configurations. (8 points)

1.      What benefit do you see to using Datagram Switching?

2.      What benefit do you see to using Virtual Circuit Switching?


8.      If UCSB is allocated the range of addresses 128.111/16 and they want to divide it into 8 equal groups of addresses, what exactly would the new ranges of addresses be? In other words, I am looking for 8 address entries in the CIDR format, each representing one of the eight networks. (6 points)

9.      Run the simulation of RIP available on the web page: http://www-mm.informatik.uni-mannheim.de/veranstaltungen/animation/routing/ripdvmrp/ Run the Demo (Edit -> Run Demo). (8 points)


    1. How many nodes does the demo start with? And how many does it add immediately afterwards?
    2. At the point where data is being sent from node 0 to node 5, why doesn’t the data go through node 4 to get to node 5?
    3. Is there a case in the demo where data goes from node 0 to node 5 through node 4? If yes, why did it choose that path this time?
    4. At the end of the demo, you see data packets going from node 0 to node 5 without passing through node 4 (i.e. path is 0 -> 2 -> 5), how without creating any new links in the layout could you make the data pass through node 4?


10.  When I send a packet over the Internet from node A to B, does the checksum in the IP header packet change or stay the same? Justify your answer. (6 points)


11.  Run a “traceroute” to a host that is at least 20 hops away and include the run with your assignment. (6 points)


12.  If you were asked to implement “traceroute”, which field in the IP header would you really use to help you implement your program? (6 points)


13.  Could you have the DF and MF bits both set to one in the same IP packet? Justify your answer. (6 points)


14.  What are the basic differences in services between TCP and UDP? (6 points)


15.   Why do we need the Source port and Destination port as part of the header in both TCP and UDP? (6 points)

Assignment Turnin

Do not forget to include your name and e-mail address as the first line of the homework.

This assignment will be turned in using the CS Department turnin program. From any computer in CSIL type the following command to turnin your answers to this homework:

csil-machine>turnin hw3@cs176a hw3.ps

Be sure to use exactly hw3@cs176a for this assignment. However the last argument is the name of the file containing your homework answers and can be any name you choose.

This assignment should be turned in a suitable format. Suitable formats include HTML, PostScript, PDF and plain text. Unfortunately, Microsoft Word documents are not suitable, they are too prone to viruses. However, that does not preclude you from using Microsoft Word to type out your answers. Simply save the Word document as an HTML file or a PostScript file if you know how. If you have any questions on a format ask the TA's.

Note: See the syllabus for the late turn-in policy. (No late assignments will be accepted.)