Computer Science for IGCSE & O level - Data Transmission (Section 13)
1
Which of the following is a critical step in the automatic repeat request (ARQ) process?
Απάντηση
(B)
The receiver sends an acknowledgement to the sender if the data is successfully received.
2
What is the objective of an echo check in data communication?
Απάντηση
(B)
To verify that the data has been received correctly.
3
In the context of packet switching, what does the term 'node' refer to?
Απάντηση
(C)
A router in the network.
4
What is the role of the private key in asymmetric encryption?
Απάντηση
(C)
To decrypt data that has been encrypted with the corresponding public key
5
What does 'ciphertext' refer to in the context of data security?
Απάντηση
(C)
The encrypted form of the message.
6
What is the biggest disadvantage of parity checks?
Απάντηση
(B)
They can only detect some types of errors.
7
In odd parity, if a data byte is 11001100, what is the value of the parity bit?
Απάντηση
(A)
0
8
Which of the following is a purpose of a public key in asymmetric encryption?
Απάντηση
(C)
Shared with anyone who wants to send encrypted messages.
9
Which of the following is an example of symmetric-key cryptography?
Απάντηση
(B)
AES
10
What type of data transmission mode is used in a standard telephone call?
Απάντηση
(C)
Full-duplex
11
What is the main advantage of symmetric encryption?
Απάντηση
(A)
High speed.
12
What is the key benefit of using a digital signature?
Απάντηση
(C)
Non-repudiation and message authenticity
13
Which of the following uses the calculated value which is a sum of values of data, the receiving computer also calculates the value from the block of data and compares the values?
Απάντηση
(C)
Checksum
14
What is 'plaintext' in the context of cryptography?
Απάντηση
(C)
The original, unencrypted data.
15
Which of the following is a characteristic of packet switching?
Απάντηση
A
C
16
Which of the following is an example of a block-level error detection method?
Απάντηση
(D)
All of the above
17
Which of the following is a function of a check digit?
Απάντηση
(B)
To detect errors during transmission.
18
What are the functionalities of ARQ?
Απάντηση
A
B
C
19
Which key is primarily used to verify the sender's identity in the digital signature process using asymmetric encryption?
Απάντηση
(A)
The public key
20
Which mode of transmission is used in a CB radio?
Απάντηση
(B)
Half-duplex
21
In a data transmission system, what is the function of parity checking?
Απάντηση
(B)
To identify errors that may occur during transmission.
22
What is the purpose of a check sum in data transmission?
Απάντηση
(B)
To detect errors in the data during transmission
23
In the ISBN-13 example, what is the function of the check digit?
Απάντηση
(B)
To ensure the ISBN number is valid.
24
What is the role of the sender in automatic repeat request (ARQ)?
Απάντηση
(B)
To retransmit data if an error is detected.
25
What is the primary function of a 'hash' function?
Απάντηση
(B)
To create a unique 'fingerprint' of the data.
26
In encryption, which of the following is the term used to describe the message before it is encrypted?
Απάντηση
(B)
Plaintext
27
Which of the following is the correct name for a form of encryption in which both the sender and the recipient use the same key to encrypt and decrypt?
Απάντηση
(A)
Symmetric key encryption
28
How is the original data sequence restored when using packet switching?
Απάντηση
(B)
Using sequence numbers in the header.
29
Which type of encryption is known for its speed and simplicity?
Απάντηση
(B)
Symmetric encryption
30
What does the term 'node' refer to within the context of packet switching?
Απάντηση
(C)
A router or other intermediary device.
31
What is the main method used by ARQ to ensure reliable data transmission?
Απάντηση
(C)
Retransmission of data.
32
Which error detection method does not rely on the addition of extra bits to the original data?
Απάντηση
(B)
Checksum
33
In a network, what is the role of a 'router'?
Απάντηση
(A)
To connect multiple networks together.
34
What is the primary objective of encrypting data?
Απάντηση
(B)
To make data unreadable to unauthorized users.
35
What are the essential components of a data packet?
Απάντηση
A
B
C
36
What security goal is achieved through encryption?
Απάντηση
(A)
Confidentiality
37
Which is the purpose of the sequence number in the header of a packet?
Απάντηση
(C)
To ensure packets are reassembled in the correct order.
38
What does ARQ stand for in the context of data transmission?
Απάντηση
(C)
Automatic Repeat Request
39
What is the primary purpose of symmetric key encryption?
Απάντηση
(C)
To encrypt data using a single key
40
In data transmission, what is the primary function of a 'checksum'?
Απάντηση
(C)
To check for errors that might occur during transmission.
41
Which method is used to verify the integrity of data during transmission?
Απάντηση
(C)
Checksums
42
For what purpose are check digits used?
Απάντηση
(B)
Error detection during data entry or scanning.
43
In even parity, if a data byte has three 1s, what will the parity bit be?
Απάντηση
(B)
1
44
What is a characteristic of asymmetric encryption?
Απάντηση
(B)
It uses a key pair (public and private).
45
Who should have access to the private key in asymmetric encryption?
Απάντηση
(C)
The receiver of the encrypted message.
46
What is a key characteristic of the term 'ciphertext'?
Απάντηση
(C)
It is unreadable without the correct key.
47
How does a checksum help in data integrity?
Απάντηση
(C)
By verifying that the data hasn't been altered during transmission.
48
What is the core concept behind an echo check?
Απάντηση
(B)
To verify data accuracy.
49
What happens if the sender receives a negative acknowledgement (NAK) in ARQ?
Απάντηση
(B)
The data is retransmitted.
50
In symmetric encryption, what does the term 'key' refer to?
Απάντηση
(A)
A secret code used to encrypt and decrypt the data.
