Unit 2: Physical and Data Link Layers - Practice Quiz

1 Which component of a data communication system sends the data?

2 What is a protocol in data communication?

3 Which guided medium consists of pairs of insulated copper wires twisted together?

4 Which transmission medium carries data as pulses of light?

5 Which unguided transmission medium commonly requires a line-of-sight path?

6 Which technology uses electromagnetic waves to transmit data without a physical cable?

7 What is the gradual loss of signal strength during transmission called?

8 What does bandwidth commonly describe in a communication channel?

9 What is the basic unit of data handled by the data link layer?

10 What is the main purpose of flow control at the data link layer?

11 What is the purpose of error detection in data communication?

12 Which method asks the sender to transmit data again after an error is detected?

13 What can a standard Hamming code do when a single-bit error occurs?

14 Where are parity bits commonly placed in a Hamming codeword?

15 What does CRC stand for?

16 In CRC, what is appended to the original data before transmission?

17 In even parity, what must the total number of bits be?

18 Which type of error can a single parity bit reliably detect?

19 How is a checksum generally used by a receiver?

20 What does a checksum mainly help detect?

21 A sender transmits an file over a link. Assuming bytes and ignoring all delays except transmission delay, how long does transmission take?

22 A full-duplex link is rated at . What transmission capability does this rating provide?

23 Two buildings in an industrial area must be connected using a high-speed cable. The route passes close to heavy electrical machinery and the buildings have different ground potentials. Which medium is most suitable?

24 Which design feature of twisted-pair cable primarily reduces crosstalk and externally induced electromagnetic noise?

25 A terrestrial microwave link must connect two stations separated by a long distance with a hill between them. Which change is most likely to make the link reliable?

26 What is the approximate wavelength of a radio signal with frequency , assuming a propagation speed of ?

27 A signal passes through an amplifier with a gain of and then through two cable sections with losses of and . What is the net gain?

28 A channel has bandwidth and a signal-to-noise ratio of . Using Shannon capacity, what is its approximate maximum data rate?

29 A -byte packet is sent over a link spanning . If the propagation speed is , what is the total transmission-plus-propagation delay?

30 A stop-and-wait protocol sends frames with a transmission time of . The one-way propagation delay is , and acknowledgment transmission time is negligible. What is the approximate link utilization?

31 In an alternating-bit stop-and-wait protocol, a receiver gets another frame with the same sequence number as the previously accepted frame. What should the receiver normally do?

32 A Go-Back-N protocol uses a -bit sequence number field. What is the largest sender window that avoids ambiguity after sequence numbers wrap around?

33 A codeword is protected by one even-parity bit. During transmission, exactly two bits of the complete codeword are inverted. What will the parity check indicate?

34 A block code has a minimum Hamming distance of . Which capability does the code have?

35 How many parity bits are required for a Hamming code containing data bits and capable of correcting one-bit errors?

36 In a Hamming code using even parity, parity bits occupy positions , , and . If data bits are placed in positions , , , and , what is the resulting codeword from position to ?

37 A sender uses the CRC generator for the dataword . What remainder is obtained after appending three zeros and performing modulo-2 division?

38 A CRC generator polynomial has degree and includes both its highest-degree and constant terms. Which burst errors are guaranteed to be detected?

39 Using an -bit one's-complement checksum, what checksum is produced for the two words and ?

40 When verifying a one's-complement checksum, a receiver adds all received data words and the checksum using end-around carry. Which result indicates that no error was detected?

41 A node begins transmitting a -byte frame over a Mbps link of length km. The propagation speed is m/s, and processing and queuing delays are negligible. How long after transmission begins does the last bit arrive at the destination?

42 A modem transmits -QAM symbols at kbaud. Exactly one of every transmitted symbols is a pilot symbol carrying no user data. Ignoring all other overhead, what is the net user bit rate?

43 A lossless transmission line is terminated by a purely resistive load. What fraction of the incident power is delivered to the load?

44 A step-index optical fiber has core radius and numerical aperture . At wavelength , which conclusion follows from its normalized frequency ?

45 A free-space radio link changes its carrier frequency from GHz to GHz while distance, transmit power, and dimensionless antenna gains remain unchanged. By approximately how much does the received power change?

46 Using the approximate line-of-sight formula , what is the maximum direct-path distance between antennas of heights m and m?

47 A noiseless signaling scheme uses distinct signal levels over a kHz channel. The actual channel has an SNR of dB. Considering both Nyquist and Shannon limits, what is the highest theoretical data rate?

48 A transmitter outputs dBm. The path includes a dB cable loss, an dBi transmitting antenna, an dB propagation loss, and an dBi receiving antenna. If receiver noise power is dBm, what is the received SNR?

49 A stop-and-wait protocol sends -byte frames over a Mbps link with a one-way propagation delay of ms. ACK transmission time, processing time, and errors are negligible. What is the sender's link utilization?

50 In an alternating-bit protocol, the receiver correctly accepts frame , but its ACK is lost. The sender times out and retransmits frame . What must the receiver do?

51 Frames use a -bit sequence number field. To avoid ambiguity after sequence-number wraparound, what are the maximum sender-window sizes for Go-Back-N and Selective Repeat, respectively?

52 A block code has minimum Hamming distance . If a received word may contain two unknown bit errors plus erasures whose positions are known, what is the largest for which correction is guaranteed?

53 Using a Hamming code with even parity, parity bits at positions , , and , and data bits placed in positions , , , and , what codeword is produced?

54 In a SECDED Hamming code, a received word has a nonzero Hamming syndrome, but the overall parity check indicates even parity. Assuming at most two bits were altered, how should the decoder classify the result?

55 A message has data bits. What is the minimum number of check bits required to construct a SECDED code using Hamming parity bits plus one overall parity bit?

56 The dataword is protected by the CRC generator . What remainder is appended to the dataword?

57 A CRC uses generator polynomial . Which error-detection guarantee is valid for every protected frame?

58 A block uses even two-dimensional parity with one parity bit per row and one per column. Which data-bit error pattern can pass both sets of parity checks undetected?

59 Using an -bit one's-complement checksum with end-around carry, what checksum is generated for the words , , and ?

60 A checksum is computed solely as the one's-complement sum of fixed-size data words, with no position-dependent fields. Which corruption is guaranteed to preserve the checksum?