V3 CH 4 & 5 KEY

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1. As part of the five-layer network model used in this textbook, the data link layer sits directly between: a. the physical and the application layers b. the network and the application layers c. the network and transport layers d. the physical and the application layers e. the physical and the network layers 2. Assume that more than one application program is using the same communications line on a particular computer. To be able to decide to which application program a message should be delivered on this computer, TCP/IP relies on the: a. data link layer address b. port address c. application layer address d. network address e. IP address 3. The transport layer must break messages from the application layer into several _____ that can be sent to the network layer. a. bits b. bytes c. frames d. segments e. strings 4. ________ is the process of sending a signal to a client that gives its permission to transmit or asks it to receive. a. Contention b. Polling c. Pooling d. Carrier sense e. CRC 5. Which of the following is true about roll call polling? a. It cannot be modified to increase priority of clients or terminals. b. It does not require a server, host, or special device that performs the polling. c. It is also called token passing. d. It is a type of contention approach to media access control. e. It typically involves some waiting because the server has to wait for a response from the polled client or terminal. 6. With contention: a. computers wait until the circuit is free before they send data b. the server or front end processor works consecutively through a list of clients to determine who should have access to the media c. the front end processor must wait for a response from the polled client or terminal d. one computer starts the poll and passes it to the next computer on the multipoint circuit e. there is never a chance for “collision,” or two computers trying to send data at the same time 7. In general, controlled approaches: a. work better than contention approaches for small networks that have low usage. b. work better than contention approaches for large networks that have high usage. c. work better than contention approaches for all sizes of networks. d. do not require a host, server, or active monitor to assign media access control. e. have many collisions. 8. In a _________, more than one data bit is changed by the error-causing condition. a. burst error

b. data rate shift c. Trellis-coded modulation d. uniform distribution e. amplitude key shift 9. Which of the following is true with respect to the data link layer? a. It accepts streams of bits from the application layer. b. It is responsible for encoding the bit-stream as a series of electronic voltages. c. It performs error detection. d. It performs routing functions. e. It organizes data from the physical layer and passes these coherent messages directly to the application layer. 10. ____________ is not a function of a data link protocol. a. Media access control b. Message delineation c. Amplitude shift keying d. Indicating when a message starts and stops e. Error control 11. Media access control: a. is not very important in point-to-point with full duplex configuration. b. is not very important in local area networks. c. is not very important in a point-to-point with a half-duplex configuration. d. is not very important in a multipoint configuration. e. does not control when computers transmit. 12. Which of the following is not a controlled access method of media access control? a. Token passing b. CSMA/CD c. polling d. roll call polling e. hub polling 13. Media access controls refer to the need to control when computers transmit. a. True b. False 14. Most computer networks managed by a host mainframe computer tend to use a form of media access control called contention. a. True b. False 15. The two categories of network errors are lost data and delimited data. a. True b. False 16. Data transmission errors typically are distributed uniformly in time. a. True b. False 17. Gaussian noise is a special type of attenuation. a. True b. False 18. Optical media is: a. more likely to suffer from noise than electrical media. b. has about the same likelihood of suffering from noise as electrical media. c. has about the same likelihood of suffering from noise as coaxial cable. d. less likely to suffer from noise than electrical media.

e. more prone to noise than twisted pair media. 19. ____________ refers to bits that have been changed, in error, from 1 to 0, or vice versa, in a data transmission. a. Contracted bits b. Polled bits c. Inverse multiplexed bits d. Flipped bits e. Bit delineation 20. ____________ refers to the type of routing in which the routing table is developed by the network manager and modifications are made only when computers are added to or removed from the network. a. Adaptive routing b. Dynamic routing c. Static routing d. Distance vector routing e. Link state routing 21. _______________ is a type of dynamic routing. a. Static routing b. Circuitous routing c. Centralized routing d. Link state e. X.25 routing 22. Another term for impulse noise is: a. Gaussian noise b. spikes c. attenuation d. cross-talk e. intermodulation noise 23. With ________ routing, computers or routers count the number of hops along a route and periodically exchange information on the hop count with their neighbors. a. circuitous b. decentralized c. distance vector d. indirect e. link state 24. Cross-talk: a. occurs when one circuit picks up signals in another. b. is always bothersome because it has a high signal strength. c. decreases with increased proximity of two wires. d. decreases during wet or damp weather. e. increases with lower frequency signals. 25. When a signal is reflected back to the transmitting equipment, it is called a(n) _________. a. white noise b. echo c. crosstalk d. attenuation e. impulse noise 26. The loss of power a signal suffers as it travels from the transmitting computer to a receiving computer is _____. a. white noise b. spiking

c. attenuation d. intermodulation noise e. echo 27. The familiar background static on radios and telephones is called: a. echoes b. intermodulation noise c. gray noise d. cross-talk e. white noise 28. The primary source of error in data communications is: a. echoes. b. intermodulation noise. c. spikes. d. attenuation. e. cross-talk. 29. __________can obliterate a group of bits, causing a burst error. a. Cross-talk b. Attenuation c. Impulse noise d. Intermodulation noise e. Gray noise 30. If a signal with a frequency of 500 MHz combines with another signal of 1500 MHz and they form a new signal of 2000 MHz, this is an example of: a. intermodulation noise b. attenuation c. echo d. white noise e. Cross-talk 31. _____________ is an effective way to prevent impulse noise, cross talk, and intermodulation noise. a. Shielding wires b. Adding fluorescent lights c. Adding repeaters to a circuit d. Adding amplifiers to a circuit e. Shorting a circuit 32. _____________ is an effective way to prevent attenuation. a. Shielding wires b. Adding fluorescent lights c. Adding repeaters or amplifiers to a circuit d. Changing multiplexing techniques e. Shorting a circuit 33. Which of the following is way to reduce or eliminate crosstalk on a circuit? a. Physically separating the cables from other communication cables b. Adding repeaters or amplifiers to a circuit c. Reducing the length of the cable d. Adding fluorescent lights e. Shorting a circuit 34. A multicast message can be used to send a message to a maximum of two other computers. a. True b. False 35. Another term for stop-and-wait ARQ is sliding window.

a. True b. False 36. A subnet mask of 255.255.0.0 means that all computers with only the same first two bytes in their IPv4 addresses are on the same subnet. a. True b. False 37. IP addresses from 224 to 239 belong to Class D and are reserved for multicasting. a. True b. False 38. IP addresses from 224 to 239 belong to Class D and are reserved for the government. a. True b. False 39. On digital circuits, we use _________ to reshape the incoming signal and prevent attenuation. a. amplifiers b. repeaters c. multiplexers d. digitizers e. modems 40. Which of the following is not an error detection method used in the data link layer? a. Parity checking b. Cyclic redundancy checking c. CRC-32 d. Pulse code checking e. Odd parity 41. With odd parity (assume that the parity bit (in bold) has been placed at the end of each of the following) and a 7-bit ASCII code, which of the following is incorrect? a. 01101011 b. 00011011 c. 00100101 d. 10110110 e. 11111110 42. The probability of detecting an error, given that one has occurred, using parity checking is about: a. 0% b. 50% c. 75% d. 98% e. 100% 43. Using parity, the probability for detecting an error, given that one has occurred, is: a. about 50% for either even or odd parity. b. about 70% for even parity and 30% for odd parity. c. about 30% for even parity and 70% for odd parity. d. about 0% for either even or odd parity. e. about 100% for either even or odd parity. 44. The probability of detecting an error, provided that one has occurred, using cyclic redundancy checking is about: a. 0% b. 75% c. 50% d. > 99% e. exactly 100%

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