# Data Link Layer

 Question 1
Consider a 100 Mbps link between an earth station (sender) and a satellite (receiver) at an altitude of 2100 km. The signal propagates at a speed of $3 \times 10^8$ m/s. The time taken (in milliseconds, rounded off to two decimal places) for the receiver to completely receive a packet of 1000 bytes transmitted by the sender is
 A 15.06 B 54.25 C 7.08 D 4.25
GATE CSE 2022   Computer Network
Question 1 Explanation:
 Question 2
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 (=$10^6$ 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 ______________
 A 180 B 160 C 135 D 115
GATE CSE 2021 SET-2   Computer Network
Question 2 Explanation:
 Question 3
Consider the cyclic redundancy check (CRC) based error detecting scheme having the generator polynomial $X^3+X+1$. Suppose the message $m_4m_3m_2m_1m_0=11000$ is to be transmitted. Check bits $c_2c_1c_0$ are appended at the end of the message by the transmitter using the above CRC scheme. The transmitted bit string is denoted by $m_4m_3m_2m_1m_0c_2c_1c_0$. The value of the checkbit sequence $c_2c_1c_0$ is
 A 101 B 110 C 100 D 111
GATE CSE 2021 SET-2   Computer Network
Question 3 Explanation:
 Question 4
Consider the sliding window flow-control protocol operating between a sender and a receiver over a full-duplex error-free link. Assume the following:

The time taken for processing the data frame by the receiver is negligible.
The time taken for processing the acknowledgement frame by the sender is negligible.
The sender has infinite number of frames available for transmission.
The size of the data frame is 2,000 bits and the size of the acknowledgement frame is 10 bits.
The link data rate in each direction is 1 Mbps ($= 10^6$ bits per second).
One way propagation delay of the link is 100 milliseconds.

The minimum value of the sender's window size in terms of the number of frames, (rounded to the nearest integer) needed to achieve a link utilization of 50% is _____________
 A 82 B 51 C 44 D 65
GATE CSE 2021 SET-1   Computer Network
Question 4 Explanation:
 Question 5
Assume that a 12-bit Hamming codeword consisting of 8-bit data and 4 check bits is $d_8d_7d_6d_5c_8d_4d_4d_3d_2c_4d_1c_2c_1$, where the data bits and the check bits are given in the following tables:

Which one of the following choices gives the correct values of x and y?
 A x is 0 and y is 0 B x is 0 and y is 1 C x is 1 and y is 0 D x is 1 and y is 1
GATE CSE 2021 SET-1   Computer Network
Question 5 Explanation:
 Question 6
Consider the following two statements.

S2: Destination MAC address of an ARP request is a broadcast address.

Which one of the following choices is correct?
 A Both S1 and S2 are true B S1 is true and S2 is false C S1 is false and S2 is true D Both S1 and S2 are false
GATE CSE 2021 SET-1   Computer Network
Question 6 Explanation:
 Question 7
Consider that 15 machines need to be connected in a LAN using 8-port Ethernet switches. Assume that these switches do not have any separate up link ports. The minimum number of switches needed is ___________.
 A 2 B 3 C 4 D 5
GATE CSE 2019   Computer Network
Question 7 Explanation:
 Question 8
Suppose that in an IP-over-Ethernet network, a machine X wishes to find the MAC address of another machine Y in its subnet. Which one of the following techniques can be used for this?
 A X sends an ARP request packet to the local gateway's IP address which then finds the MAC address of Y and sends to X B X sends an ARP request packet to the local gateway's MAC address which then finds the MAC address of Y and sends to X C X sends an ARP request packet with broadcast MAC address in its local subnet D X sends an ARP request packet with broadcast IP address in its local subnet
GATE CSE 2019   Computer Network
Question 8 Explanation:
 Question 9
StationA uses 32 byte packets to transmit messages to Station B using a sliding window protocol. The round trip delay between A and B is 80 ms and the bottleneck bandwidth on the path between A and B is 128 kbps. What is the optimal window size that A should use?
 A 20 B 40 C 160 D 320
ISRO CSE 2018   Computer Network
Question 9 Explanation:
 Question 10
________ can detect burst error of length less than or equal to degree of the polynomial and detects burst errors that affect odd number of bits.
 A Hamming Code B CRC C VRC D None of the above
ISRO CSE 2018   Computer Network
Question 10 Explanation:
There are 10 questions to complete.

### 11 thoughts on “Data Link Layer”

1. Question number 37, it suld be 46.4 microseconds not miliseconds. Please correct it

• Thank you for your suggestion. We have updated it.

2. question 10: options should be in Bps not bps

3. Sorry question no:42

• Thank you for your suggestion. We have updated it.

4. For the question no: 40 The answer have to be 25%. Please do correct it.

• Thank you MOUNIKA DASA,
We have updated the answer.

5. In Qestion no 13 data is missing
propagation speed of link is ( 2×10^8 meter per second ) not millisecond please correct it.