Data Link Layer Answer Key

Data Link Layer True-False Questions The following are possible True/False questions for tests. The statement is given and the answer is provided in square brackets. The level of difficulty (easy, moderate, difficult) and the page number(s) relevant to the topic are also furnished. 1. 2. 3. 4. Media access controls refer to the need to control when computers transmit. Answer: True Difficulty: Easy Reference: Media Access Control The data link layer accepts messages from the network layer and controls the hardware that transmits them. Answer: True Difficulty: Moderate Reference: Introduction Only the sender of a data transmission needs to be concerned about the rules or protocols that govern how it communicates with the receiver Answer: False Difficulty: Easy Reference: Introduction Most computer networks managed by a host mainframe computer use contention media access control. 5. Answer: False Difficulty: Moderate Reference: Controlled Access Polling is the process of permitting all clients to transmit or receive at any time. 6. Answer: False Difficulty: Moderate Reference: Controlled Access With roll-call polling, a server polls clients in a consecutive, pre-arranged priority list. 7. Answer: True Difficulty: Easy Reference: Controlled Access Token passing is a term that refers to hub polling, in which one computer starts a poll and passes it to the next computer on a multipoint circuit. Answer: True Difficulty: Easy Reference: Controlled Access 8. With contention, a computer does not have to wait before it can transmit. A computer can transmit at anytime. 9. Answer: False Difficulty: Moderate Reference: Contention Contention is commonly used with Ethernet local area networks. 10. Answer: True Difficulty: Easy Reference: Contention Controlled access MAC approaches work better in a large network with high usage. 11. 12. 13. Answer: True Difficulty: Easy Reference: Relative Performance In a network, the type of errors caused during data transmission can be controlled by the network hardware and software. Answer: True Difficulty: Easy Reference: Error Control The two categories of network errors are: lost data and delimited data. Answer: False Difficulty: Easy Reference: Error Control If a computer transmits a message containing “ABC” and the destination computer receives “abc” as the message, the message is corrupted. 14. Answer: True Difficulty: Moderate Reference: Error Control In data transmission, data errors are uniformly distributed in time. 15. Answer: False Difficulty: Easy Reference: Error Control Undesirable stray electrical voltage can cause data communication errors. 16. Answer: True Difficulty: Moderate Reference: Sources of Errors Gaussian noise is a special type of attenuation. Answer: False Difficulty: Moderate Reference: Sources of Errors 17. 18. 19. 20. 21. 22. 23. 24. 25. Impulse noise is caused by the thermal agitation of electrons. Answer: False Difficulty: Easy Reference: Sources of Errors Crosstalk occurs when the signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Answer: True Difficulty: Moderate Reference: Sources of Errors Attenuation refers to the loss of signal strength. Answer: True Difficulty: Easy Reference: Sources of Errors When the signals from two circuits combine to form a new signal that falls into a frequency band reserved for another signal, this is called, intermodulation noise. Answer: True Difficulty: Moderate Reference: Sources of Errors Wired Ethernet is standardized as IEEE802.11. Answer: False Difficulty: Easy Reference: Ethernet The distance between repeaters or amplifiers on a telephone circuit is determined by the amount of power gained per unit length of the transmission. Answer: False Difficulty: Moderate Reference: Error Prevention When we amplify the signal on an analog circuit, we also amplify any noise that is present on the circuit. Answer: True Difficulty: Easy Reference: Error Prevention For effective error detection and correction, extra error detection “data” must be included with each message Answer: True Difficulty: Moderate Reference: Error Detection In an odd parity-checking scheme, the parity bit is set to make the total number of ones in the byte (including the parity bit) an even number. Answer: False Difficulty: Easy Reference: Parity Checking 26. Parity checking can only detect an error when an even number of bits are switched. 27. Answer: False Difficulty: Moderate Reference: Parity Checking Cyclical redundancy check is one of the most popular polynomial error-checking schemes. 28. Answer: True Difficulty: Easy Reference: Cyclical Redundancy Check The simplest method for error correction is retransmission. 29. Answer: True Difficulty: Easy Reference: Error Correction via Retransmission Another term for stop-and-wait ARQ is sliding window. 30. Answer: False Difficulty: Easy Reference: Continuous ARQ One type of forward error correction is the Hamming code. 31. Answer: True Difficulty: Moderate Reference: How Forward Error Correction Works Forward error correction is commonly used in satellite transmission. 32. Answer: True Difficulty: Easy Reference: Forward Error Correction HDLC is very similar to the SDLC synchronous data link protocol. 33. Answer: True Difficulty: Moderate Reference: High-Level Data Link Control Point-to-point Protocol is a byte-count-oriented protocol. 34. 35. Answer: True Difficulty: Easy Reference: Point-to-Point Protocol Overhead bits are used for error checking and marking the start and end of characters and packets. Answer: True Difficulty: Easy Reference: Transmission Efficiency Transmission efficiency refers to the percentage of bits transmitted without errors. Answer: False Difficulty: Moderate Reference: Transmission Efficiency MULTIPLE CHOICE The following are possible multiple-choice questions for tests. The question is posed and the answer is provided under the choices. The level of difficulty (easy, moderate, difficult) and the page number(s) relevant to the topic is also furnished. 1. 2. 3. 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 Answer: E Difficulty: Easy Reference: Introduction 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 getting a message from one computer to another (one node to another) without errors. c. It does not perform error detection. d. It performs routing functions. e. It organizes data from the physical layer and passes these coherent messages to the application layer. Answer: B Difficulty: Moderate Reference: Introduction ____________ 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 Answer: C Difficulty: Moderate Reference: Introduction 4. 5. 6. 7. 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 Answer: A Difficulty: Easy Reference: Media Access Control 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 Answer: B Difficulty: Easy Reference: Controlled Access ________ 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 Answer: B Difficulty: Moderate Reference: Controlled Access Which of the following is true about roll call polling? a. It can not be modified to increase priority of clients or terminals. b. It does not require a server or 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. Answer: E Difficulty: Moderate Reference: Controlled Access 8. 9. 10. 11. 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 Answer: A Difficulty: Easy Reference: Contention 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 Answer: B Difficulty: Moderate Reference: Relative Performance 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 Answer: A Difficulty: Moderate Reference: Error Control Errors on a network can occur: a. only on dial-up type of circuits b. because of noise on the line c. only on poorly maintained networks d. only due to Gaussian noise e. only due to lightning strikes Answer: B Difficulty: Moderate Reference: Sources of Errors 12. 13. 14. 15. 16. The first sublayer of the data link layer is the a. logical link control sublayer b. media access control sublayer c. session sublayer d. physical sublayer e. transport sublayer Answer: A Difficulty: Moderate Reference: Introduction Which of the following media is least susceptible to noise? a. fiber optic cable b. coaxial cable c. twisted pair d. unshielded twisted pair e. shielded twisted pair Answer: A Difficulty: Sources of Errors 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 Answer: D Difficulty: Moderate Reference: Sources of Errors ____________ 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 Answer: D Difficulty: Moderate Reference: Sources of Errors Another term for impulse noise is: a. Gaussian noise b. spikes c. attenuation d. cross-talk e. intermodulation noise Answer: B Difficulty: Moderate Reference: Sources of Errors 17. 18. 19. 20. 21. The familiar background static on radios and telephones is called: a. echoes b. intermodulation noise c. impulse noise d. cross-talk e. white noise Answer: E Difficulty: Moderate Reference: Sources of Errors The primary source of error in data communications is: a. echoes b. intermodulation noise c. spikes d. attenuation e. cross-talk Answer: C Difficulty: Moderate Reference: Sources of Errors __________can obliterate a group of bits, causing a burst error. a. Cross-talk b. Attenuation c. Impulse noise d. Intermodulation noise e. White noise Answer: C Difficulty: Moderate Reference: Sources of Errors 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 Answer: A Difficulty: Moderate Reference: Sources of Errors 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 Answer: B Difficulty: Moderate Reference: Sources of Errors 22. 23. 24. 25. 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 Answer: C Difficulty: Moderate Reference: Sources of Errors If a signal with a frequency of 500 MHz combines with a 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 Answer: A Difficulty: Moderate Reference: Sources of Errors When the output signal from an amplifier on a circuit is different from the input signal, this is called _________________. a. intermodulation noise b. attenuation c. echo d. white noise e. cross-talk Answer: E Difficulty: Moderate Reference: Sources of Errors A phase hit is likely to be: a. spikes b. a short term shift out of phase c. intermodulation noise d. white noise e. Gaussian noise Answer: B Difficulty: Moderate Reference: Sources of Errors 26. 27. 28. 29. _____________ 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 Answer: A Difficulty: Easy Reference: Error Prevention _____________ 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 Answer: C Difficulty: Moderate Reference: Error Prevention Which of the following is way to reduce or eliminate crosstalk on a circuit, a. changing multiplexing techniques b. adding repeaters or amplifiers to a circuit c. reducing the length of the cable d. adding fluorescent lights e. shorting a circuit Answer: A Difficulty: Moderate Reference: Error Prevention On digital circuits, we use _________ to reshape the incoming signal and prevent attenuation. a. amplifiers b. repeaters c. multiplexers d. digitizers e. modems Answer: B Difficulty: Moderate Reference: Error Prevention 30. 31. 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 Answer: D Difficulty: Moderate Reference: Error Detection 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. b. c. d. e. 32. 33. 01101011 00011011 00100101 10110110 11111110 Answer: B Difficulty: Moderate Reference: Parity Checking The probability of detecting an error, given that one has occurred, using parity checking is about: a. 100% b. 0% c. 50% d. 75% e. 98% Answer: C Difficulty: Easy Reference: Parity Checking 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 Answer: A Difficulty: Moderate Reference: Parity Checking 34. 35. 36. 37. The probability of detecting an error, provided that one has occurred, using cyclic redundancy checking is about: a. 75% b. 0% c. exactly 100% d. 50% e. > 99% Answer: E Difficulty: Easy Reference: Cyclical Redundancy Check ARQ means that: a. a receiver that detects an error in a message simply asks the sender to retransmit the message until it is received without error b. the common carrier Automatically Returns Queries to the subscriber upon receipt of such queries c. a sender is using a data link protocol called Asynchronous Repeating reQuest d. a fiber optic cable meets the American Registered Quality, a certification standard for use in high-quality data communication transmission lines e. a sender is using a parity scheme called Array Resource Quality Answer: A Difficulty: Moderate Reference: Error Correction via Retransmission In ARQ, a NAK: a. is sent by the recipient if the message was received without error b. is sent by the sender at the same time as it sends a data packet c. is sent by the recipient if the message contains an error d. refers to non-asynchronous Kermit technique e. means that the sender should continue with sending the next message Answer: C Difficulty: Moderate Reference: Stop-and-Wait ARQ Stop-and-wait ARQ uses ___________ type of data flow. a. full simplex b. half complex c. full duplex d. half duplex e. full complex Answer: D Difficulty: Moderate Reference: Stop-and-Wait ARQ 38. 39. 40. 41. With __________ ARQ, the sender pauses for a response from the receiver to alter each message or packet of data. a. open window b. halt and be recognized (HBR) c. sliding window d. stop and wait e. continuous Answer: D Difficulty: Moderate Reference: Stop-and-Wait ARQ With __________ ARQ, the sender immediately sends the next message or packet of data. a. continuous b. immediate c. open window d. stop-and-wait e. halt and be recognized (HBR) Answer: A Difficulty: Moderate Reference: Continuous ARQ ______________ controls errors by detecting and correcting them at the receiving end without retransmission of the original message. a. Hamming code b. Huffman encoding c. Front end processing d. Wave division multiplexing e. Hub polling Answer: A Difficulty: Moderate Reference: How Forward Error Correction Works Asynchronous transmission: a. is used to transmit each character simultaneously with all other characters b. has a pre-determined, fixed time between sending characters c. is typically used on multipoint half duplex circuits d. uses a continuous series of start bits as an idle signal e. is also known as start-stop transmission Answer: E Difficulty: Moderate Reference: Asynchronous Transmission 42. 43. 44. 45. 46. Which of the following is not a type of synchronous protocol? a. SDLC b. VT100 c. HDLC d. Ethernet e. PPP Answer: B Difficulty: Moderate Reference: Synchronous Transmission Synchronous transmission: a. cannot be used on multipoint circuits b. is used to send one character at a time c. uses start bits before each character to be sent d. uses stop bits after each character to be sent e. is used to transmit a “frame” or “packet” of data at a time Answer: E Difficulty: Moderate Reference: Synchronous Transmission Which of the following is true about the data link protocol, SDLC: a. It is a client-server protocol developed by Compaq in 1996 b. It is a byte-count-oriented protocol c. It uses a special bit pattern called a flag at the beginning and end of every frame (or packet) d. It uses a contention media access control protocol e. It does not have a problem with transparency Answer: C Difficulty: Moderate Reference: Synchronous Data Link Control Which of the following is true about the data link protocol, Ethernet (IEEE 802.3)? a. it is not very popular b. it is a bit-oriented protocol c. it uses block check characters for error detection d. newer version permits jumbo frames e. it uses parity bits for error detection Answer: D Difficulty: Moderate Reference: Ethernet Which of the following is true about the data link protocol, PPP? a. it is commonly used in WANs b. it is a bit-oriented protocol c. it uses block check characters for error detection d. it was developed in the 1970s e. it uses parity bits for error detection Answer: A Difficulty: Moderate Reference: Data Link Protocols 47. 48. 49. 50. In communication protocols, _________ are used to convey the user’s meaning. a. information bits b. overhead bits c. stop bits d. start bits e. flag bits Answer: A Difficulty: Moderate Reference: Transmission Efficiency _________________ is defined as the total number of information bits divided by the total number of bits in the transmission. a. Asynchronous rate b. Protocol percentage c. Throughput d. Transmission Rate of Information Bits e. Transmission efficiency Answer: E Difficulty: Moderate Reference: Transmission Efficiency Calculating the actual throughput of a data communication network is: a. not normally required for synchronous networks because they are so fast b. complex because many factors affect throughput c. simple because packet size is the primary factor affecting throughput d. not needed for satellite-based networks e. far less complicated if the system operates on a contention basis Answer: B Difficulty: Easy Reference: Transmission Efficiency TRIB, an acronym that relates to throughput, stands for: a. Throughput Reduction of Information Barriers b. Transmission Rate of Information Bits c. Throughput Rate of Iso-synchronous Bytes d. Transmission Regulation for Inverse-multiplexing Bands e. Trellis-coded Regulation of Information Bits Answer: B Difficulty: Moderate Reference: Transmission Efficiency