Unit 3: Data link layer - Practice Quiz

1 What is a single-bit error in data communication?

2 What is a burst error?

3 Which technique adds one extra bit to make the number of 1s even or odd?

4 What is the main purpose of a checksum?

5 What is the main purpose of framing at the data link layer?

6 Which method uses special characters to mark the beginning and end of a frame?

7 Which data link layer protocol is commonly associated with point-to-point communication?

8 Which protocol is commonly used for communication on a traditional shared Ethernet network?

9 What is the purpose of flow control?

10 What is the purpose of error control?

11 In Stop-and-wait ARQ, what does the sender normally do after sending a frame?

12 What usually happens when a Stop-and-wait ARQ frame is not acknowledged?

13 In Go-back-N ARQ, what does the sender do after detecting a lost frame?

14 How many frames can a Go-back-N sender transmit before receiving acknowledgments?

15 What is a key feature of Selective Repeat ARQ?

16 In Selective Repeat ARQ, can the receiver store correctly received out-of-order frames?

17 What is the main purpose of a multiple access control protocol?

18 Which method allows a device to transmit when it has data, without a fixed transmission schedule?

19 Which controlled-access method gives permission to transmit by passing a special token?

20 Which channelization technique divides a channel into separate frequency bands?

21 The transmitted bit sequence is 10110010, but the receiver obtains 11110110. If bit positions are counted from the left, how should this error be classified?

22 A Hamming code must protect 11 data bits and correct any single-bit error. What is the minimum number of parity bits required?

23 Using CRC, the dataword 1101 is divided by the generator 1011. What codeword should be transmitted?

24 In a byte-oriented framing protocol, FLAG marks frame boundaries and ESC is the escape byte. How is the payload [A, FLAG, ESC, B] transmitted after byte stuffing?

25 A bit-oriented protocol inserts a 0 after every sequence of five consecutive 1s in the payload. What is the stuffed form of 01111110?

26 An HDLC station needs to acknowledge received frames and advertise its readiness without carrying user data. Which type of HDLC frame should it use?

27 Frames of 1000 bits are sent over a 1 Mbps link with a one-way propagation delay of 3 ms. Ignoring acknowledgment transmission time, what is the maximum utilization with a sliding window of four frames?

28 A frame takes 2 ms to transmit, and the one-way propagation delay is 8 ms. If acknowledgment transmission time is negligible, what is the approximate utilization of Stop-and-Wait ARQ?

29 In Stop-and-Wait ARQ, a receiver accepts frame 0, but its acknowledgment is lost. When frame 0 arrives again after the sender times out, what should the receiver do?

30 A Go-Back-N ARQ protocol uses 3-bit sequence numbers. What is the largest permitted sender window size?

31 In Go-Back-N ARQ, frames 4, 5, 6, and 7 are sent, but frame 4 is lost. Frames 5, 6, and 7 reach the receiver. Which frames are retransmitted after timeout?

32 A Selective Repeat ARQ implementation uses 3-bit sequence numbers. What is the maximum safe sender window size?

33 In Selective Repeat ARQ, frame 4 is lost while frames 5 and 6 arrive correctly. What action is normally taken?

34 Before transmitting data, stations use designated mini-slots to request future transmission slots. Which multiple-access category best describes this method?

35 A large number of stations use Slotted ALOHA under ideal conditions. What is the maximum normalized throughput of the channel?

36 A 10 Mbps CSMA/CD network has a maximum one-way propagation delay of . Ignoring other delays, what minimum frame length is needed to detect a worst-case collision?

37 In a polling-based network, a primary station sequentially invites secondary stations to transmit. Which issue most directly reduces the reliability of this arrangement?

38 A token-passing network detects that the token has been lost because no station has transmitted for a specified interval. What recovery action is required?

39 A 1.2 MHz link is divided into four equal FDM channels with three 20 kHz guard bands between adjacent channels. What bandwidth is available to each data channel?

40 In a synchronous CDMA system, station A uses the chip code . Which code is orthogonal to A's code?

41 A 12-bit dataword is transmitted as 101100111010, but the receiver obtains 101000011010. Which characterization is most accurate?

42 A CRC system uses generator polynomial of degree . Which condition guarantees that every burst error of length at most is detected?

43 For a binary Hamming code that corrects one-bit errors and uses an additional overall parity bit, what is the strongest standard guarantee?

44 A byte-oriented protocol uses the flag byte 7E and escape byte 7D. Under byte stuffing, a payload contains 7D 7E 7D. What byte sequence is transmitted between the flags?

45 In a reliable full-duplex data-link protocol using piggybacked acknowledgments, a receiver has an acknowledgment pending but no outbound data. What is the principal design trade-off?

46 A receiver advertises a window of 5 frames, while the sender's congestion or protocol window permits 8 frames. Ignoring network-layer congestion control, how many additional unacknowledged frames may the sender legally transmit?

47 A stop-and-wait link has frame transmission time , one-way propagation delay , and ACK transmission time . With no losses and negligible processing time, what is the sender utilization?

48 In alternating-bit ARQ, a sender retransmits a frame after its ACK is lost. The receiver has already delivered that frame. Which mechanism prevents duplicate delivery?

49 With -bit sequence numbers, what is the maximum sender window size for Go-back-N ARQ if the receiver accepts only the next in-order frame?

50 A Go-back-N sender transmits frames 0 through 5. Frame 2 is lost, but frames 3 through 5 arrive. If cumulative ACKs identify the next expected frame, what ACK information should the receiver repeatedly provide?

51 A Selective Repeat protocol uses -bit sequence numbers. To avoid ambiguity between old and new frames after sequence-number wraparound, what is the largest safe sender window?

52 In Selective Repeat, frames 4, 5, and 7 arrive while frame 6 is lost. Which receiver behavior is correct?

53 A shared channel has offered load under pure ALOHA and slotted ALOHA. Which comparison is correct at their respective maximum-throughput points?

54 In nonpersistent CSMA, a station senses a busy channel. Which action best describes the protocol?

55 For CSMA/CD, a sender must detect a collision before finishing transmission of the minimum-size frame. If the maximum round-trip propagation delay is , what condition is required?

56 In a token-passing network, a station fails while holding the token. Which recovery issue must the protocol address?

57 A reservation-based controlled-access protocol uses one reservation bit per station per cycle. If 10 stations participate and 4 reserve transmission, what is the principal efficiency trade-off?

58 In FDMA, adjacent users are separated by guard bands. If each user requires bandwidth and each guard band requires width , how much spectrum is required for users arranged contiguously?

59 A TDMA system assigns each of 8 users a slot in every frame. If each slot carries 1000 bits and each frame lasts 2 ms, what is the per-user data rate, ignoring guard time?

60 In ideal synchronous CDMA, two users employ spreading codes and . Which property allows the receiver to separate their simultaneous transmissions by correlation?