CS 455: Computer Networks and Data Communication Sample Final Examination Points: 125 Time allowed: 180 minutes CLOSED BOOK, CLOSED NOTES, OPEN MIND Answer All Questions (Note: This sample exam does not cover Chapter 8. But the final exam does cover it. Make a note of this.) Turning in this exam under your name confirms your continued support for the honor code of Old Dominion University and further indicates that you have neither received nor given assistance in completing it. Name: ______________________________ SSN: _________________ Question # 1 2 3 4 5 Bonus Total Possible points 25 25 25 25 25 5 125 Obtained points FINAL ANSWER SHOULD BE WRITTEN IN THE ALLOTTED TABLES. CS 455: Sample Final Examination 1 Question 1: a. Using Dijkstra’s shortest path algorithm, determine the shortest distance and shortest path from A to F. (Start the algorithm from node A). Show your work. (For your reference, a description of the algorithm is reproduced from the book in the appendix.) B 10 A 3 5 D 4 E 17 2 F 6 12 7 C 2 G b. If flooding is used as a routing algorithm to send a packet P from node A to F (in the below network), show the flow of packet P from A to F. (Show all flows due to P from A) B D E A F C G c. Using distance vector routing, compute the new routing table at B (in the above network) when it has received the following tables from A, D, and E. The delay from B to A, D, and E is 2, 5, and 5, respectively. A 0 10 3 15 1 12 10 D 10 8 15 0 13 3 5 4 5 9 11 0 4 4 E CS 455: Sample Final Examination 2 Question 2: a. Using the following network diagram, show how hop-by-hop choke packets may be used to slow down the sender node A that is currently sending packets to node F using the path A-CG-F. B D E A F C G b. An application produces output in terms of 2-Mbyte bursts. Each burst has a 20 milliseconds duration, and bursts occur at a constant interval of 500 milliseconds (i.e., 2 in a second). The application lasts for 2 seconds. It is connected to an 8-Mbps network through a token bucket. Suppose the token bucket is initially filled to capacity with 12 Mbits, show (schematically) the variation in the output from the token bucket until all the application data is transmitted. Tokens arrive into the bucket at the rate of 5Mbps. (Note: Assume that each token allows 1 bit.) c. Convert the IP address whose hexadecimal representation is D22C1470 to dotted decimal notation. CS 455: Sample Final Examination 3 Question 3: a. A packet was sent from node A to node F using IP protocol. It was fragmented as follows along the way (at nodes C and G). What are the value of fragment offset, DF, and MF fields for F1, F2, and F3 when received at node F? 1000 Node A 300 300 F1 700 360 F2 Node C 340 Node G F3 Node F b. A company uses NAT (Network Address Translation) to connect multiple workstations (WS) to the internet using a single IP address (203.45.103.67) provided by its ISP. Show how packets sent from a specific WS (10.23.52.201) to another workstation (125.25.43.98) are handled by the NAT. (Use the specific data given. Don’t simply write some generic answer.) WS NAT 10.23.52.201 ISP Router 203.45.103.67 WS 125.25.43.98 c. What are the implications of not having a checksum field in the IPv6 header? What happens when a packet is received in error at the destination? CS 455: Sample Final Examination 4 Question 4: a. How do you explain the absence of source address and destination address fields in the TCP header? b. Host H1 intends to establish a TCP connection with host H2. List the sequence of steps that take place at H1 and H2 before H1 starts sending its data on the connection. c. Explain the significance of the following three states in the TCP connection management finite-state diagram. (i) FIN WAIT 1 (ii) FIN WAIT 2 (iii) TIME WAIT CS 455: Sample Final Examination 5 Question 5: a. The timer management module of a TCP connection had an initial estimate of RTT of 20 milliseconds and a deviation of 5 milliseconds. It has a smoothing factor of 0.7. It is then observed that the next two TPDUs had an RTT of 40 and 10 milliseconds, respectively. Determine the current values of RTT, D, and timeout values (after both TPDUs were received). b. What problem does Nagle’s algorithm solve? How does it solve the problem? c. What is silly window syndrome? How does Clark’s algorithm solve this problem? CS 455: Sample Final Examination 6