# Computer Network

 Question 1
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      Data Link Layer
Question 1 Explanation:
 Question 2
Consider a computer network using the distance vector routing algorithm in its network layer. The partial topology of the network is shown below. The objective is to find the shortest-cost path from the router R to routers P and Q. Assume that R does not initially know the shortest routes to P and Q. Assume that R has three neighboring routers denoted as X, Y and Z. During one iteration, R measures its distance to its neighbors X, Y, and Z as 3, 2 and 5, respectively. Router R gets routing vectors from its neighbors that indicate that the distance to router P from routers X, Y and Z are 7, 6 and 5, respectively. The routing vector also indicates that the distance to router Q from routers X, Y and Z are 4, 6 and 8 respectively. Which of the following statement(s) is/are correct with respect to the new routing table o R, after updation during this iteration?
[MSQ]
 A The distance from R to P will be stored as 10 B The distance from R to Q will be stored as 7 C The next hop router for a packet from R to P is Y D The next hop router for a packet from R to Q is Z
GATE CSE 2021 SET-2      Network Layer Protocol
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      Data Link Layer
Question 3 Explanation:
 Question 4
Consider the three-way handshake mechanism followed during TCP connection establishment between hosts P and Q. Let X and Y be two random 32-bit starting sequence numbers chosen by P and Q respectively. Suppose P sends a TCP connection request message to Q with a TCP segment having SYN bit =1, SEQ number =X, and ACK bit =0. Suppose Q accepts the connection request. Which one of the following choices represents the information present in the TCP segment header that is sent by Q to P?
 A SYN bit =1, SEQ number =X+1, ACK bit =0, ACK number =Y, FIN bit =0 B SYN bit =0, SEQ number =X+1, ACK bit =0, ACK number =Y, FIN bit =1 C SYN bit =1, SEQ number =Y, ACK bit =1, ACK number =X+1, FIN bit =0 D SYN bit =1, SEQ number =Y, ACK bit =1, ACK number =X, FIN bit =0
GATE CSE 2021 SET-2      Transport Layer Protocol
Question 4 Explanation:
 Question 5
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      Data Link Layer
Question 5 Explanation:
 Question 6
Consider two hosts P and Q connected through a router R. The maximum transfer unit (MTU) value of the link between P and R is 1500 bytes, and between R and Q is 820 bytes.
A TCP segment of size 1400 bytes was transferred from P to Q through R, with IP identification value as 0x1234. Assume that the IP header size is 20 bytes. Further, the packet is allowed to be fragmented, i.e., Don't Fragment (DF) flag in the IP header is not set by P.
Which of the following statements is/are correct?
[MSQ]
 A Two fragments are created at R and the IP datagram size carrying the second fragment is 620 bytes. B If the second fragment is lost, R will resend the fragment with the IP identification value 0x1234. C If the second fragment is lost, P is required to resend the whole TCP segment. D TCP destination port can be determined by analysing only the second fragment.
GATE CSE 2021 SET-1      Transport Layer Protocol
Question 6 Explanation:
 Question 7
A TCP server application is programmed to listen on port number P on host S. A TCP client is connected to the TCP server over the network.
Consider that while the TCP connection was active, the server machine S crashed and rebooted. Assume that the client does not use the TCP keepalive timer. Which of the following behaviors is/are possible?
[MSQ]
 A If the client was waiting to receive a packet, it may wait indefinitely. B The TCP server application on S can listen on P after reboot. C If the client sends a packet after the server reboot, it will receive a RST segment. D If the client sends a packet after the server reboot, it will receive a FIN segment.
GATE CSE 2021 SET-1      Transport Layer Protocol
Question 7 Explanation:
 Question 8
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      Data Link Layer
Question 8 Explanation:
 Question 9
Consider the following two statements.

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      Data Link Layer
Question 9 Explanation:
 Question 10
Checksum field in TCP header is
 A ones complement of sum of header and data in bytes B ones complement of sum of header, data and pseudo header in?16?bit words C dropped from IPv6 header format D better than md5 or sh1 methods
ISRO CSE 2020      Transport Layer Protocol
Question 10 Explanation:

There are 10 questions to complete.

### 1 thought on “Computer Network”

1. Question 60 is wrongly tagged here, it belongs to object oriented programming. 