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FACULTY OF SCIENCE AND AGRICULTURE SPRING SESSION EXAMINATION 2004 ITC242 INTRODUCTION TO DATA COMMUNICATIONS DAY & DATE: WRITING TIME: TIME: Three (3) Hours READING TIME: Ten minutes MATERIALS SUPPLIED BY UNIVERSITY: 1 x 24pp Answer Booklet General Purpose Answer Sheet MATERIALS PERMITTED IN EXAMINATION: Pens and Pencils, Calculator 2B pencil, eraser NUMBER OF QUESTIONS: Part A: Thirty (30) multiple choice questions Part B: Ten (10) short answer questions Part C: One (1) essay question INSTRUCTIONS TO CANDIDATES: 1. 2. 3. 4. 5. 6. Mark your answers to the multiple choice questions, Part A, on the general purpose answer sheet. Write your answers to the written questions, Parts B and C, in the booklet provided. Multiple choice questions are worth one mark each. (Total of 30 marks) Short Answer questions are worth 5 marks each. (Total of 50 marks) Essay question is worth 20 marks. (Total of 20 marks) A total mark possible is 100. INSTRUCTIONS TO INVIGILATORS: 1. QUESTION PAPER MUST BE COLLECTED STUDENT NAME: STUDENT SIGNATURE: STUDENT NO: PART A: Multiple Choice Questions (Each question is worth 1 mark each. Answer the questions on the general purpose answer sheet provided). 1. At which layer of the TCP/IP protocol suite would you find an email program? a. b. c. d. Transport Presentation Application Session 2. Using Shannon’s theorem, S(f) = f log2 (1 + W/N), where S(f) is the maximum data transfer rate, f is the frequency of the signal, W is the power of the signal in watts and N is the power of the noise in watts, calculate the data transfer rate given the following information: signal frequency = 10,000 Hz, signal power = 5000 watts, noise power = 1,666 watts. a. b. c. d. 10,000 bps 20,000 bps 30,000 bps 40,000 bps 3. Given Nyquist’s theorem, C = 2f log2(L) where C is the channel capacity, f is the frequency of the signal, and L is the number of signal levels, what is the channel capacity of a signal that has 8 different levels and a frequency of 10,000 Hz? a. b. c. d. 18,062 bps 30,000 bps 60,000 bps 160,000 bps 4. Which term describes the process where data is packaged with necessary protocol information as it passes through layers of the OSI reference model? a. b. c. d. Wrapping Encryption Encapsulation Protocolisation 5. The sharing of a medium and its link by two or more devices is called a. b. c. d. Modulation Encoding Line discipline Multiplexing 6. What component of a coaxial cable makes it less susceptible to noise than twisted-pair cable? a. b. c. d. Outer conductor shielding A single inner conductor Twisted core conductor pairs Diameter of cable 7. What is the maximum baud rate of a digital signal that employs Differential Manchester encoding and has a data rate of 1000bps? a. b. c. d. 500 baud 1000 baud 2000 baud 4000 baud 8. The bandwidth for a data transmission line that transmits within a frequency range of 100 Hz to 3,500 Hz is: a. b. c. d. 3,000 Hz. 3,400 Hz. 3,500 Hz. 3,600 Hz. 9. The ____________________ of a signal is the number of times a signal makes a complete cycle within a given time frame. a. b. c. d. Bandwidth Frequency Amplitude Spectrum 10. In a sliding window Go-Back-N ARQ system, A sends packets 0,1,2,3,4,5 and 6. Packet 3 arrives at B corrupted. What do A and B send to each other next? a. b. c. d. B sends REJ-3 , A then sends packets 3,4,5,6,7,0 and 1 B sends REJ-2, A then sends packets 3,4,5,6,7,0 and 1 B sends REJ-3, A then sends just packet 3 B sends REJ-2, A then sends just packet 3 11. In a sliding window scheme, acknowledgements contain a value _____ the number of the next expected packet. a. b. c. d. greater than equal to less than equal to or greater than 12. The _____ is the data transfer rate agreed on by both customer and frame relay carrier. a. b. c. d. constant bit rate customer transfer rate committed information rate approved data rate 13. A logarithmic loss as a function of distance and the resistance within the wire is: a. b. c. d. attenuation noise amplitude spectrum 14. _____ uses frequency hopping and direct sequence techniques. a. b. c. d. Frequency modulation Differential Manchester Pulse code modulation Spread spectrum 15. Which of the following is FALSE regarding transmission impairments? a. Thermal noise is distributed across the frequency spectrum and is therefore difficult to eliminate. b. Impulse noise is often referred to as white noise. c. Attenuation causes an electromagnetic signal to become gradually weaker over distance. d. Guided transmission media such as physical cable can be designed to reduce the affects of Cross Talk noise. 16. A network style where the application and presentation logic resides on the client and the data storage logic resides on a server is called: a. b. c. d. Client/Server Client Based Host Base Peer-to-Peer 17. The physical layout of a Local Area Network is called a. b. c. d. Contention Nodes Topology None of the above 18. Ethernet is said to be non-deterministic because of which of the following? a. It is not possible to determine how long it will take to get a frame from one device to another. b. It is not possible to determine whether an error has occurred during the transmission of a frame. c. It is not possible to determine if another device wishes to transmit. d. It is not possible to determine the maximum time a device will have to wait to transmit. 19. When a bridge receives a packet that has a destination MAC address located on a different segment from which it came, the packet is: a. b. c. d. Forwarded Blocked Repeated on all segments All of the above 20. The purpose of the token in a token ring is: a. b. c. d. To control who gets to transmit next To listen to medium, if no one is transmitting, then allow transmission To listen for collisions To eliminate broadcasts 21. ISDN basic rate interface (BRI) multiplexes _______________ separate channels. a. b. c. d. One Two Three Four 22. The start and stop bit in Asynchronous transmission is used to ensure: a. b. c. d. that the total number of bits is a factor of 10 a continuous stream of data that single bit errors do not occur the receiver maintains synchronization with the sender 23. ____________________ is a very powerful error detection technique and should be considered for data transmission systems. a. b. c. d. Vertical redundancy check Cyclic redundancy checksum Simple parity Horizontal parity 24. The CSMA/CD network is described by which frame specification? a. b. c. d. IEEE 802.2 IEEE 802.3 IEEE 802.4 IEEE 802.5 25. In a ____________________ subnet, no unique dedicated physical path is established to transmit the data packets across the subnet. a. b. c. d. Circuit-switched Packet-switched Large Heavily loaded 26. The length of an IP address is: a. b. c. d. 8 bits 16 bits 32 bits 48 bits 27. What is the protocol that allows dynamic assignment of IP Addresses to workstations? a. b. c. d. ICMP DHCP SMTP SNMP 28. The equation to calculate availability is? a. b. c. d. (Total Available Time + Downtime) * Total Available Time (Total Available Time - Downtime) (Total Available Time + Downtime) (Total Available Time - Downtime) / Total Available Time 29. With Public Key Encryption: a. messages that cannot be encoded are returned to the sender b. data compression is provided c. knowledge of the encryption algorithm and the encryption key determines the decryption key; d. a pair of keys are needed for encryption and decryption of messages e. none of the above 30. A _____ cipher replaces a character or group of characters with a different character or group of characters. a. b. c. d. polyalphabetic substitution-based monoalphabetic substitution-based transposition-based network-based PART B: Short Answer Questions (Each question is worth 5 marks each. Answer the questions in the Answer booklet provided. Use diagrams where appropriate to enhance your answers.) 1. A 30 minutes telephone conversation is recorded and stored digitally using Pulse Code Modulation at 8000 samples per second. If each sample is encoded as 8-bits, how many floppy disks are required to store the conversation if each floppy disk can take 1.44 MB? (Show all working and assumptions) 2. On a certain network 1,000,000 bytes of data needs to be transmitted using Asynchronous transmission, using 7 data bits, 1 start bit, 2 stop bits and 1 parity bit. If the transmission is at 56kbps, how long would it take to complete the transmission and what would be the overhead in time? Assume there are 8 bits in a byte. (Show all working and assumptions) 3. On a certain network 1,000,000 bytes of data needs to be transmitted using Synchronous transmission where each frame is 8000 bits in total of which 48 bits are overhead. If the transmission is at 56kbps, how long would it take to complete the transmission and what would be the overhead in time? (Show all working and assumptions) 4. What do we mean when we say that a signal is “analogue”? 5. Describe the function of a router. At what layer of the OSI model does it operate? 6. List the types of transmission impairment that unshielded twisted pair cable can suffer from. Provide a clear definition for each impairment. 7. What is the difference between a deterministic and a non-deterministic protocol? 8. What are three relative advantages and three relative disadvantages of circuit switching and packet switching? 9. Name four (4) types of multiplexing giving a brief explanation of each. 10. Compare and contrast conventional encryption and public-key encryption. PART C: Essay Question (This question is worth 20 marks. Answer the question in the Answer booklet provided Use diagrams where appropriate to enhance your answer.) 1. Name and describe in as much detail as you can each of the seven layers of the OSI reference model?