CN Data Link Layer

Question 31

A network with CSMA/CD protocol in the MAC layer is running at 1 Gbps over a 1 km cable with no repeaters. The signal speed in the cable is 2 x 10⁸ m/sec. The minimum frame size for this network should be 

• 10000 bits
  

• 10000 bytes
  

• 5000 bits
  

• 5000 bytes
  

Question 32

A channel has a bit rate of 4 kbps and one-way propagation delay of 20 ms. The channel uses stop and wait protocol. The transmission time of the acknowledgement frame is negligible. To get a channel efficiency of at least 50%, the minimum frame size should be  

• 80 bytes
• 80 bits
• 160 bytes
• 160 bits

Question 33

In a TDM medium access control bus LAN, each station is assigned one time slot per cycle for transmission. Assume that the length of each time slot is the time to transmit 100 bits plus the end-to-end propagation delay. Assume a propagation speed of 2 x 10⁸ m/sec. The length of the LAN is 1 km with a bandwidth of 10 Mbps. The maximum number of stations that can be allowed in the LAN so that the throughput of each station can be 2/3 Mbps is

• 3
• 5
• 10
• 20

Question 34

Consider the following message M = 1010001101. The cyclic redundancy check (CRC) for this message using the divisor polynomial x⁵ + x⁴ + x² + 1 is :  

• 01110

• 01011

• 10101

• 10110

Question 35

A sender uses the Stop-and-Wait ARQ protocol for reliable transmission of frames. Frames are of size 1000 bytes and the transmission rate at the sender is 80 Kbps (1Kbps = 1000 bits/second). Size of an acknowledgement is 100 bytes and the transmission rate at the receiver is 8 Kbps. The one-way propagation delay is 100 milliseconds. Assuming no frame is lost, the sender throughput is __________ bytes/second.

• 2500
• 2000
• 1500
• 500

Question 36

In an Ethernet local area network, which one of the following statements is TRUE ?

• A station stops to sense the channel once it starts transmitting a frame.
• The purpose of the jamming signal is to pad the frames that are smaller than the minimum frame size.
• A station continues to transmit the packet even after the collision is detected.
• The exponential backoff mechanism reduces the probability of collision on retransmissions

Question 37

A network has a data transmission bandwidth of 20 × 10⁶ bits per second. It uses CSMA/CD in the MAC layer. The maximum signal propagation time from one node to another node is 40 microseconds. The minimum size of a frame in the network is _________ bytes. Note : This question was asked as Numerical Answer Type.

• 200
• 250
• 400
• 1200

Question 38

Consider a 128×10³ bits/second satellite communication link with one-way propagation delay of 150 milliseconds. Selective retransmission (repeat) protocol is used on this link to send data with a frame size of 1 kilobyte. Neglect the transmission time of acknowledgment. The minimum number of bits required for the sequence number field to achieve 100% utilization is ___________

• 2
• 4
• 6
• 8

Question 39

A 1Mbps satellite link connects two ground stations. The altitude of the satellite is 36,504 km and speed of the signal is 3 × 10⁸ m/s. What should be the packet size for a channel utilization of 25% for a satellite link using go-back-127 sliding window protocol? Assume that the acknowledgment packets are negligible in size and that there are no errors during communication.

• 120 bytes
• 60 bytes
• 240 bytes
• 90 bytes

Question 40

The minimum frame size required for a CSMA/CD based computer network running at 1 Gbps on a 200m cable with a link speed of 2 × 10⁸m/s is

• 125 bytes
• 250 bytes
• 500 bytes
• None of these