U.G.C. NET Exam. Dec. 2020-June 2021 Paper II (COMPUTER SCIENCE & APPLICATIONS)

Total Questions: 100

91. Match List-I with List-II

Correct Answer: (a) A ‐ IV, B ‐ III, C ‐ I, D ‐ II
Solution:

Data Link Layer : pigybacking is sometimes referred to as "wi-fi squatting". The usual purpose of piggybacking is simply to gain free network access rather than any malicious intent, but it can slow down data transfer for legitimate users of network.
Transport Layer : Responsible for true end-to-end layer from source to destination. It is termed as and endto-end layer because it provides a point to point connection rather than hop to hop. It reliably deliver the services between the source-host and destination host.
Session Layer : is responsible for establishing managing, synchronizing and termination session between end-user application processes. It works as a dialog, controller. It allows the system to communicate in either. Half duplex or full duplex mode of communication. It is responsible for token management.
Network Layer :- subnet usage accounting : has accounting functions to keep track of frames forwarded by subnet intermediate systems, to produce billing information.

92. Given below are two statements

Statement I : Telnet, Ftp, Http are application layer protocol
Statement II: The Iridium project was planned to launch 66 low orbit satellites.
In light of the above statements, choose the correct answer from the options given below:

Correct Answer: (a) Both Statement I and Statement II are true
Solution:Both Statement I and Statement II are true

93. Which of the following statement is False?

Correct Answer: (e) *
Solution:

Packet– Switched networks move data in separate, small packets based on the destination address in each packet. When received, packets are reassembled in the proper sequence to make up the message.
Circuit- Switched networks : required dedicated pointto-point connections during calls.
• Packet switching leads to better utilization of bandwidth resources than circuit switching // Because data move in packets therefore better use of resources.
• Packet switching results in less variation in delay than circuit switching // Queueing delay flunctuation is more in packet switching as there is no dedicated path.
• Packet switching requires more per packet processing than circuit switching // All the info needs to be in packet as well as packet reassembling has to be done at end therefore more processing.
• Packet switching can lead to reordering unlike in circuit switching // because reassembling is done at destination, packing reordering might occur.

94. In Ethernet when Manchester coding is used, the bit rate is__________.

Correct Answer: (a) Half the baud rate
Solution:

In manchester encoding, 2 signals changes to represent a bit. So the baud rate = 2*bit rate so that bit rate is half the baud rate

95. The address of class B host is to be split into subnets with 6‐bit subnet number. What is the maximum number of the subnets and the maximum number of hosts in each subnet?

Correct Answer: (d) 62 subnets and 1022 hosts
Solution:

In class B

96. In electronic mail, which of the following protocols allows the transfer of multimedia?

Correct Answer: (d) MIME
Solution:

IMAP :- is for the retrieval of emails and SMTP is for the sending of emails. That means IMAP talks to both the client and server to get emails, and SMTP talks only to servers to send emails.
POP3/IMAP :- Post office protocol (POP) is an application layer Internet standard protocol used by local e-mail clients to retrieve email from a remote server over a TCP/IP connection. Virtually all modern e-mail clients and servers support POP3, and it along with IMAP (Internet Message Access Protocols) are the two most prevalent Internet standard protocols for email retrieval, with IMAP (Internet Message Access Protocol) are the two most prevalent Internet standard protocols for emails retrieval, with many webmail service provides such as Google mail, Microsoft mail and Yahoo!
MIME :- MIME stands for multipurpose Internet mail Extensions. It is used to extend the capabilities of Internet e-mail protocols such as SMTP. The MIME protocols allows the users, to exchange various types of digital content such as pictures, audio, video, and various types of documents and files in the e-mails.

97. A message is encrypted using public key cryptography to send a message from sender to receiver. Which one of the following statements is True?

Correct Answer: (a) Sender encrypts using receiver's public key
Solution:

In Public key cryptography, both sender and receiver generate a pair of keys, – public key and private key. Public keys are known globally. suppose A is sender and B is the receiver. So, A has 3 keys :
1. Public key of A (everyone knows)
2. Private key of A (only A knows)
3. Public key of B (Everyone knows)
And B also has 3 keys :
1. Public key of B (Everyone knows)
2. Private key of B (only B knows)
3. Public key of A (Everyone knows)
•Anything that is encrypted using public key of A can be decrypted only using private key of A. • Anything that is encrypted using private key of A can be decrypted only using public key of A. • Anything that is encrypted using public key of B can be decrypted only using private key of B. • Anything that is encrypted using private key of B can be decrypted only using public key of B. Now A wants to send a secret message to B. so for encryption : A has following 3 options :
1- Public key of A (Everyone knows) : So for decryption B needs - Private key of A - only A knows it. So, B will not be able to decrypt it.
2. Private key of A (only A knows) So, for decryption B needs - public key of A - Everyone known it. So everyone can decrypt it. So it is of no use.
3. Public key of B (Everyone knows) : So, for decryption B needs - private key of B - only B knows it. So only B will able to decrypt it (That's what we want) So for providing security. Sender encrypts using receiver's public key and Receiver decrypts using his own.
So, connect option is (A) sender encrypts using receiver's public key.

98. Which of the following statements are true?

A. Frequency division multiplexing technique can be handled by digital circuits.
B. Time division multiplexing technique can be handled by analog circuits
C. Wavelength division multiplexing technique is used with optical fiber for combining two signals.
D. Frequency division multiplexing technique can be applied when the bandwidth of a link is greater than the bandwidth of the signals to be transmitted.
Choose the correct answer from the options given below:

Correct Answer: (b) C and D only
Solution:C and D only

99. Which of the following statements are true?

A. X.25 is connection-oriented network
B. X.25 doesn't support switched virtual circuits.
C. Frame relay service provides acknowledgements.
D. Frame relay service provides detection of transmission errors.
Choose the correct answer from the options given below:

Correct Answer: (a) A and D only
Solution:A and D only

100. Let G(x) be the generator polynomial used for CRC checking. The condition that should be satisfied by the G(x) to catch all errors consisting of an odd number of inverted bits is:

Correct Answer: (a) (x+1) is factor of G(x)
Solution:(x+1) is factor of G(x)