2021 · Paper 1

Complete GATE CSE 2021 Paper 1 overview, original pages and practice · Timed previous-paper practice

Questions 55–57 of 65. Imported answers require review unless explicitly marked reviewed.

Question 45

Open question

CSMSQ2 marksNeeds review

Consider two hosts



and



connected through a router



. The maximum transfer unit (MTU) value of the link between



and



is 1500 bytes, and between



and



is 820 bytes. A TCP segment of size 1400 bytes was transferred from



to



through



, 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



. Which of the following statements is/are correct?

Your answerSelect all correct options. You can choose more than one.

A.

Two fragments are created at



and the IP datagram size carrying the second fragment is 620 bytes.

B.

If the second fragment is lost,



will resend the fragment with the IP identification value 0x1234.

C.

If the second fragment is lost,



is required to resend the whole TCP segment.

D.

TCP destination port can be determined by analysing only the second fragment.

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Question 46

Open question

CSMSQ2 marksNeeds review

Consider the following pseudocode, where S is a semaphore initialized to 5 in line#2 and counter is a shared variable initialized to 0 in line#1. Assume that the increment operation in line#7 is not atomic.

int counter = 0;

Semaphore S = init(5);

void parop(void)

{



wait(S);



wait(S);



counter++;



signal(S);



signal(S);

} If five threads execute the function parop concurrently, which of the following program behavior(s) is/are possible?

Your answerSelect all correct options. You can choose more than one.

A.

The value of counter is 5 after all the threads successfully complete the execution of parop.

B.

The value of counter is 1 after all the threads successfully complete the execution of parop.

C.

The value of counter is 0 after all the threads successfully complete the execution of parop.

D.

There is a deadlock involving all the threads.

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Question 47

Open question

CSMSQ2 marksNeeds review

Consider a dynamic hashing approach for 4-bit integer keys:

There is a main hash table of size 4.

The 2 least significant bits of a key is used to index into the main hash table.

Initially, the main hash table entries are empty.

Thereafter, when more keys are hashed into it, to resolve collisions, the set of all keys corresponding to a main hash table entry is organized as a binary tree that grows on demand.

First, the 3rd least significant bit is used to divide the keys into left and right subtrees.

To resolve more collisions, each node of the binary tree is further sub-divided into left and right subtrees based on the 4th least significant bit.

A split is done only if it is needed, i.e., only when there is a collision. Consider the following state of the hash table.



Which of the following sequences of key insertions can cause the above state of the hash table (assume the keys are in decimal notation)?

Your answerSelect all correct options. You can choose more than one.

A.

5, 9, 4, 13, 10, 7

B.

9, 5, 10, 6, 7, 1

C.

10, 9, 6, 5, 13

D.

9, 5, 13, 6, 10, 14

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