Chapter 2 Definitions

Question 1

Define data packet

Answer 1

A small part of a message/data that is transmitted over a network; after transmission all the data packets are reassembled to form the original message/data

Question 2

Define packet header

Answer 2

The part of the data packet that contains the IP addresses of the sender and receiver, and includes the packet number which allows reassembly of the data packets

Question 3

Define cyclic redundancy check (CRC)

Answer 3

An error checking method in which all the 1-bits in the data packet payload are added and the total is stored in the packet trailer; the same calculation is repeated at the receiving station

Question 4

Define payload

Answer 4

The actual data being carried in a data packet

Question 5

Define node

Answer 5

Stages in a network that can receive and transmit data packets; routers are nodes in communication networks

Question 6

Define packet switching

Answer 6

A method of transmission in which a message is broken into many data packets which can then be sent along pathways independently of each other

Question 7

Define router

Answer 7

A device that enables data packets to be moved between different networks

Question 8

Define real time streaming

Answer 8

The transmission of data over a network for live events where the data is sent as soon as it is received or generated

Question 9

Define hopping/hop number

Answer 9

A number in a data packet header used to stop data packets that never reach their destination from ‘clogging up’ the data paths/routes

Question 10

Define simplex

Answer 10

Data that can be sent on one direction only

Question 11

Define half-duplex

Answer 11

Data that can be sent in both directions but not at the same time

Question 12

Define full-duplex

Answer 12

Data that can be sent in both directions at the same time (simultaneously)

Question 13

Define serial data transmission

Answer 13

Sending data down one channel at a time

Question 14

Define parallel data transmission

Answer 14

Sending data down several channels/wires several bits at a time

Question 15

Define skewed (data)

Answer 15

Data that arrives at the destination with the bits no longer synchronised

Question 16

Define universal serial bus (USB)

Answer 16

A type of serial data transmission which has become the industry standard for connecting computers to devices via a USB port

Question 17

Define parity check

Answer 17

A method used to check if data has been transferred correctly; it makes use of even parity or odd parity

Question 18

Define parity bit

Answer 18

A bit added to a byte of data in the most significant bit position; this ensures that the byte follows the correct even parity or odd parity protocol

Question 19

Define parity block

Answer 19

A horizontal and vertical parity check on a block of data being transmitted

Question 20

Define parity byte

Answer 20

An extra byte of data sent at the end of a parity block; it is composed of the parity bits generated from a vertical parity check of the data block

Question 21

Define checksum

Answer 21

A verification method used to check if data transferred has been altered or corrupted; calculated from the block of data of data being sent; the checksum value is sent after each data block

Question 22

Define automatic repeat request (ARQ)

Answer 22

A method of checking transmitted data for errors; it makes use of acknowledgement and timeout to automatically request re-sending of data if the time interval before positive acknowledgement is too long

Question 23

Define acknowledgement

Answer 23

A message sent to the receiver indicating that data has been received correctly (used in the ARQ error detection method)

Question 24

Define timeout

Answer 24

The time interval allowed to elapse before an acknowledgement is received (in the ARQ error detection method)

Question 25

Define echo check

Answer 25

A method used to check if data has been transferred correctly; data is sent to a receiver and then immediately sent back to the sender; the sender then checks if the received data matches the sent data

Question 26

Define check digit

Answer 26

An additional digit appended to a number to check if the entered number is error-free; check digit is a data entry check and not a data transmission check

Question 27

Define eavesdropper

Answer 27

Another name for a hacker who intercepts data being transmitted on a
wired or wireless network

Question 28

Define encryption

Answer 28

The process of making data meaningless using encryption keys; without the correct decryption key the data cannot be decoded (unscrambled)

Question 29

Define plaintext

Answer 29

The original text/message before it is put through an encryption algorithm

Question 30

Define ciphertext

Answer 30

Encrypted data that is the result of putting a plaintext message through an encryption algorithm

Question 31

Define encryption algorithm

Answer 31

A complex piece of software that takes plaintext and generates an
encrypted string known as ciphertext

Question 32

Define symmetric encryption

Answer 32

A type of encryption in which the same encryption key is used both
to encrypt and decrypt a message

Question 33

Define asymmetric encryption

Answer 33

A type of encryption that uses public keys and private keys to
ensure data is secure

Question 34

Define public key

Answer 34

A type of encryption key that is known to all users

Question 35

Define private key

Answer 35

A type of encryption key which is known only to the single computer/user

Question 36

Define quantum computer

Answer 36

A computer that can perform very fast calculations; it can perform
calculations that are based on probability rather than simple 0 or 1 values; this gives a quantum computer the potential to process considerably more data than existing computers