CDA 4527: Computer Communication Networks

Fall 2005

Home                      Lecture notes                        Assignment

Homework 3 (covering chapter 4, 5, 6)

(assigned 11/03; due: 11/17 in class by submitting homework in paper)

Chapter 4:

1. Chapter 4, problem 13.

2. Chapter 4, problem 21 (show your programming code in your submitted homework paper).

3. Distance vector routing: Suppose a network has 5 nodes denoted as A, B, C, D, and E. The following is the distance table in router E. Answer the following questions:

   a). Show the routing table in this router E.

   b). Router E directly connects to which routers?

   c). If a packet goes out router E directly to router A, and the final destination is router C. What is the cost known by router E?

4. Distance vector routing (no need to generate programming code, just use your hand to manually calculate as shown in the class lecture notes).

Consider the network shown in the figure below with the indicated static link costs. Considering the distance vector routing algorithm, and its current state (right after initialization phase, "-" indicates infinity). Assume that all nodes exchange messages with their neighbors within one time step.

• What are the new distance tables for nodes A, B, C and D?
• Which nodes have changed their route after this step is complete?
• Which nodes will send which updated values to which neighbors for the next step of the computation (after the current step is complete)?

5. Chapter 4, problem 29. Also answer why the network Y does not know about the existence of network B?

Chapter 5:

6. What MAC protocol does Ethernet use? What MAC protocol does 802.11b wireless LAN use? Why Ethernet has a much higher transmission efficiency than slotted ALOHA? What are the basic differences between Ethernet switch and hub?

7. Two-dimensional parity scheme: Consider the data bit stream  10101 01000 01110 10001 00001. use the 2-dimensional parity code that has 5 rows and 5 columns (use even parity scheme)

    a). Write out the parity code in the matrix format as shown in lecture slides Chapter5-part1.ppt  (page 10)

    b). Suppose the received data bit stream is 10101 01100 01110 10001 00001, which has one bit error. Explain how you use the parity code to detect this bit error.

8. Chapter 5, problem 4 (page 494).

9. Chapter 5, problem 5.

Chapter 6:

10. What is the working radio frequency and bandwidth of 802.11b, 802.11g, and 802.11a ? Why wireless MAC protocol does not use "collision detection"?

11. Compared with Ethernet MAC protocol, wireless MAC protocol has added DIFS, SIFS, RTS, CTS. Explain their full names, where are they used? Why wireless MAC protocol uses RTS/CTS?

12. Chapter 6, problem 1 (page 560).