2 Data transmission

Question 1

What is data broken down into when transmitted?

Answer 1

Packets

Question 2

What are the different sections of a data packet?

Answer 2

Packet header, payload, trailer

Question 3

What does the packet header contain?

Answer 3

Destination address, packet number, originators address

Question 4

What is the payload of a packet? How is the data overall transmitted?

Answer 4

The actual data being transmitted. The data is broken into many small units and sent as the payload in each packet

Question 5

What is the trailer (footer) of a packet?

Answer 5

Contains marker to indicate it is the end of the packet, and the data for any error detection systems used

Question 6

What are the addresses in the packet header of a packet (type)? What is this type of address?

Answer 6

Normally internet protocol (IP) addresses, unique address given to a device when it is connected to a network

Question 7

What is packet switching?

Answer 7

A method of transmitting data across a network, each packet able to take an individual pathway across the network to the destination

Question 8

What is a router and what does it do in packet switching?

Answer 8

A network component which examines a data packet to obtain its destination address and then decides which pathway to send the packet along to reach this address

Question 9

What is a network?

Answer 9

Computers and devices joined together using cables or wireless technology

Question 10

What are the different types of data transmission methods?

Answer 10

Serial, parallel (number of wires); simplex, half-duplex, full-duplex (direction of data transmission)

Question 11

What is serial data transmission and where might it be used?

Answer 11

A transmission method where data is sent one bit at a time down a single wire, suitable for transmission over long distances

Question 12

What are the advantages and disadvantages of serial data transmission?

Answer 12

Should arrive in order, lower chance of data skewed; less chance of interference; cheaper; transmission slower; additional data needed to indicate transmission start and stop (start bit and stop bit)

Question 13

What is parallel data transmission and where might it be used?

Answer 13

A transmission method where data is sent multiple bits at a time down multiple wires, suitable for transmission over shorter distances, approximately 5 metres

Question 14

What are the advantages and disadvantages of parallel data transmission?

Answer 14

Transmission quicker; many devices use parallel transmission internally, no need to convert to serial transmission to transmit across network; bits don’t arrive in order, higher chance of skewed; more chance of interference and error in data; more expensive

Question 15

What is simplex data transmission and where might it be used?

Answer 15

Transmission method where data is transmitted in single direction only, used when connecting a keyboard to computer

Question 16

What is half-duplex data transmission and where is it used?

Answer 16

Transmission method where data is transmitted it both directions, but only one direction at a time, Wi-Fi uses half-duplex data transmission

Question 17

What is full-duplex data transmission?

Answer 17

Transmission method where data is transmitted in both directions simultaneously, used in telephones

Question 18

What is the universal serial bus (USB)?

Answer 18

An industry standard used to transmit data

Question 19

What is a USB port?

Answer 19

A socket which is part of a device or computer that enables a USB cable or USB device to be inserted

Question 20

What is a USB cable?

Answer 20

A type of transmission media that uses the USB method to transmit data, can be used to connect devices

Question 21

What is a USB connection?

Answer 21

Collective name for using a USB cable plugged into a USB port to transfer data, special type of connection designed to transmit data at high speeds

Question 22

What is a USB device?

Answer 22

A device that plugs into a USB port on a computer and transmits data using a USB connection

Question 23

What are the advantages and disadvantages of the USB interface?

Answer 23

Simple interface, less error in devices likely to be made; speed relatively high; USB interface is universal standard; connections after first shouldn’t need download of drivers; connection can power a device; USB cable length limited, normally to 5 metres; speed not as high as other connection types like ethernet

Question 24

What is ethernet?

Answer 24

A type of connection that can be used to transmit data within a network

Question 25

What are error detection methods?

Answer 25

Procedures used to detect errors in data so actions can be taken to correct them

Question 26

What are some error detection methods?

Answer 26

Parity check, checksum, echo check, automatic repeat request (ARQ), check digit

Question 27

What is a parity check and how does it work?

Answer 27

A type of error detection method that adds an additional parity bit to each byte to create odd or even sum of 1s, (depends on odd or even parity check used), if device finds byte with number of 1s different from parity check, it knows error has occurred

Question 28

What is a checksum and how does it work?

Answer 28

An error detection method which performs a calculation on data to create checksum value, added to data and value calculated from received data, two values compared, if different, an error has occurred and been detected

Question 29

What is an echo check?

Answer 29

An error detection method where receiving device transmits received data back to sending device, which compares data. If data sent and received doesn't match, error has occurred and is detected

Question 30

What is an automatic repeat request and its ways of operating?

Answer 30

An error detection method where acknowledgement whether data is received correctly or not, and timeout, a period of time set and used to wait for an acknowledgement to be received, are used, ARQ can operate using a positive or negative acknowledgement method

Question 31

How does the positive acknowledgement method of an automatic repeat request (ARQ) work?

Answer 31

The receiving device sends a positive acknowledgement back to sender when no errors detected, next data packet send; if sender doesn't receive positive acknowledgement in time, timeout occurs and sender keep resending data packet until positive acknowledgement received or a limit reached

Question 32

How does the negative acknowledgement method of an automatic repeat request (ARQ) work?

Answer 32

If receiving device detects errors, negative acknowledgement sent back to sender, after which sender resends data packet, if sender doesn't receive negative acknowledgement within set timeframe, next data packet sent

Question 33

What is a check digit and how does it work?

Answer 33

An error detection method used for data entry, check digit value previously calculated and stored with data, check digit recalculated when data is entered, if check digits don't match, data entered is incorrect

Question 34

What is encryption?

Answer 34

A method of securing data for storage or transmission that scrambles it and makes it meaningless

Question 35

What is plain and cipher text, and how is the latter generated?

Answer 35

Data before encryption is plain text, an encryption key is an algorithm which is used to scramble the data and make it meaningless, the result being cipher text

Question 36

What are the two main methods of encryption?

Answer 36

Symmetric and asymmetric encryption

Question 37

What is symmetric encryption?

Answer 37

Plain text is encrypted into cipher text using encryption key, cipher text and encryption key are separately sent to receiving device, which uses same key to decrypt cipher text back into plain text

Question 38

How does asymmetric encryption work?

Answer 38

Plain text encrypted into cipher text using public key, cipher text transmitted to receiving device, cipher text decrypted using a private key, cnanot be decrypted using the public key