CN Data Link Layer

Question 21

A 2 km long broadcast LAN has 10⁷ bps bandwidth and uses CSMA/CD. The signal travels along the wire at 2 × 10⁸ m/s. What is the minimum packet size that can be used on this network?

• 50 bytes

• 100 bytes

• 200 bytes

• None of these

Question 22

Host A is sending data to host B over a full duplex link. A and B are using the sliding window protocol for flow control. The send and receive window sizes are 5 packets each. Data packets (sent only from A to B) are all 1000 bytes long and the transmission time for such a packet is 50 µs. Acknowledgement packets (sent only from B to A) are very small and require negligible transmission time. The propagation delay over the link is 200 us. What is the maximum achievable throughput in this communication?

• A
• B
• C
• D

Question 23

In serial data transmission, every byte of data is padded with a ‘0’ in the beginning and one or two ‘I’ s at the end of byte because

• Receiver is to be synchronized for byte reception
• Receiver recovers lost ‘0’ and ‘1’s from these padded bits
• Padded bits are useful in parity computation
• None of these

Question 24

Consider a LAN with four nodes S1, S2, S3 and S4. Time is divided into fixed-size slots, and a node can begin its transmission only at the beginning of a slot. A collision is said to have occurred if more than one node transmit in the same slot. The probabilities of generation of a frame in a time slot by S1, S2, S3 and S4 are 0.1, 0.2, 0.3 and 0.4, respectively. The probability of sending a frame in the first slot without any collision by any of these four stations is _________.

• 0.462
• 0.711
• 0.5
• 0.652

Question 25

Suppose that the stop-and-wait protocol is used on a link with a bit rate of 64 kilobits per second and 20 milliseconds propagation delay. Assume that the transmission time for the acknowledgment and the processing time at nodes are negligible. Then the minimum frame size in bytes to achieve a link utilization of at least 50% is _________.

• 160
• 320
• 640
• 220

Question 26

Consider a CSMA/CD network that transmits data at a rate of 100 Mbps (10⁸ bits per second) over a 1 km (kilometre) cable with no repeaters. If the minimum frame size required for this network is 1250 bytes, what is the signal speed (km/sec) in the cable?

• 8000
• 10000
• 16000
• 20000

Question 27

Which one of the following statements is FALSE?

• Packet switching leads to better utilization of bandwidth resources than circuit switching.
• Packet switching results in less variation in delay than circuit switching.
• Packet switching requires more per packet processing than circuit switching
• Packet switching can lead to reordering unlike in circuit switching

Question 28

Consider a simplified time slotted MAC protocol, where each host always has data to send and transmits with probability p = 0.2 in every slot. There is no backoff and one frame can be transmitted in one slot. If more than one host transmits in the same slot, then the transmissions are unsuccessful due to collision. What is the maximum number of hosts which this protocol can support, if each host has to be provided a minimum through put of 0.16 frames per time slot?

• 1
• 2
• 3
• 4

Question 29

Which of the following statements is TRUE about CSMA/CD  

• IEEE 802.11 wireless LAN runs CSMA/CD protocol
• Ethernet is not based on CSMA/CD protocol
• CSMA/CD is not suitable for a high propagation delay network like satellite network
• There is no contention in a CSMA/CD network

Question 30

Which of the following statements is FALSE regarding a bridge?

• Bridge is a layer 2 device
• Bridge reduces collision domain
• Bridge is used to connect two or more LAN segments
• Bridge reduces broadcast domain