CN Data Link Layer

Question 111

Consider a network using the pure ALOHA medium access control protocol, where each frame is of length 1,000 bits. The channel transmission rate is 1 Mbps (=10⁶ bits per second). The aggregate number of transmissions across all the nodes (including new frame transmissions and retransmitted frames due to collisions) is modelled as a Poisson process with a rate of 1,000 frames per second. Throughput is defined as the average number of frames successfully transmitted per second. The throughput of the network (rounded to the nearest integer) is ______________ .

• 130 to 140
• 140 to 150
• 120 to 130
• 100 to 110

Question 112

Consider the cyclic redundancy check (CRC) based error detecting scheme having the generator polynomial X³+X+1. Suppose the message m₄m₃m₂m₁m₀ = 11000 is to be transmitted. Check bits c₂c₁c₀ are appended at the end of the message by the transmitter using the above CRC scheme. The transmitted bit string is denoted by m₄m₃m₂m₁m₀c₂c₁c₀. The value of the checkbit sequence c₂c₁c₀ is

• 101
• 110
• 100
• 111

Question 113

Consider a link with packet loss probability of 0.2. What is the expected number of transmissions it would take to transfer 200 packets given that the stop and wait protocol is used?

• 125
• 250
• 225
• 150

Question 114

Assume that Source S and Destination D are connected through an intermediate router R. How many times a packet has to visit the network layer and data link layer during a transmission from S to D?

• Network layer – 4 times, Data link layer – 4 times
• Network layer – 4 times, Data link layer – 6 times
• Network layer – 2 times, Data link layer – 4 times
• Network layer – 3 times, Data link layer – 4 times

Question 115

An Ethernet frame that is less than the IEEE 802.3 minimum length of 64 octets is called

• Short frame

• Small frame

• Mini frame

• Runt frame

Question 116

Match the following:

• (1)

• (2)

• (3)

• (4)

Question 117

How many bytes of data can be sent in 15 seconds over a serial link with baud rate of 9600 in asynchronous mode with odd parity and two stop bits in the frame?

• 10,000 bytes
• 12,000 bytes
• 15,000 bytes
• 27,000 bytes