CS 176A -- Introduction to Computer Communication Networks
Homework Assignment #3
Due in Class, Tuesday, November 19, 2002

  1. 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.

    • What benefit do you see to using Datagram Switching?

    • What benefit do you see to using Virtual Circuit Switching?

    • Do you think the simulation is realistic? Why or why not?

  2. The Type of Service field of the IP header has two unused bits. Intuitively, having two unused bits is wasteful. Discuss why eliminating the two unused bits is difficult.

  3. Consider sending a 3000 byte datagram into a link that has an MTU of 500 bytes. How many fragments are generated? What are their characteristics (i.e. what are the flags and offset values for each)?

  4. A router is blasting out IP packets whose total length (data plus header) is 1024 bytes. Assuming that packets live for 10 seconds, what is the maximum line speed the router can operate at without danger of cycling through the IP datagram ID number space? Now assume that packets are 40 bytes long (e.g. IP and TCP but with no data), what is the new maximum line speed?

  5. Suppose that instead of using 16 bits for the network part of a class B address originally, 20 bits had been used. How many class B networks would there have been?

  6. Can the following IP addresses be aggregated:,,, If so, to what? If not, why not?

  7. 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?

  8. Explain how traceroute works. Include a traceroute to a host at least 20 hops away.

  9. Use the shortest path simulation applet from the web page: http://www.cs.uwa.edu.au/undergraduate/courses/230.300/readings/graphapplet/dijkstra.html

    • Can you design a network with unreachable nodes? Why or why not?

    • Design a network in which the shortest path found from node a to node b is six hops while the minimal hop path is only three hops. Print your network and turn it in with your assignment.

  10. Run the simulation of RIP available on the web page: http://www-mm.informatik.uni-mannheim.de/veranstaltungen/animation/routing/ripdvmrp/

    • Provide a high-level description of how the protocol functions.

    • Generate a case where data packets are sent but never reach the destination. How did you generate this test case? In other words, what conditions are present when this case occurs?