2 Data transmission Flashcards
What is data broken down into when transmitted?
Packets
What are the different sections of a data packet?
Packet header, payload, trailer
What does the packet header contain?
Destination address, packet number, originators address
What is the payload of a packet? How is the data overall transmitted?
The actual data being transmitted. The data is broken into many small units and sent as the payload in each packet
What is the trailer (footer) of a packet?
Contains marker to indicate it is the end of the packet, and the data for any error detection systems used
What are the addresses in the packet header of a packet (type)? What is this type of address?
Normally internet protocol (IP) addresses, unique address given to a device when it is connected to a network
What is packet switching?
A method of transmitting data across a network, each packet able to take an individual pathway across the network to the destination
What is a router and what does it do in packet switching?
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
What is a network?
Computers and devices joined together using cables or wireless technology
What are the different types of data transmission methods?
Serial, parallel (number of wires); simplex, half-duplex, full-duplex (direction of data transmission)
What is serial data transmission and where might it be used?
A transmission method where data is sent one bit at a time down a single wire, suitable for transmission over long distances
What are the advantages and disadvantages of serial data transmission?
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)
What is parallel data transmission and where might it be used?
A transmission method where data is sent multiple bits at a time down multiple wires, suitable for transmission over shorter distances, approximately 5 metres
What are the advantages and disadvantages of parallel data transmission?
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
What is simplex data transmission and where might it be used?
Transmission method where data is transmitted in single direction only, used when connecting a keyboard to computer
What is half-duplex data transmission and where is it used?
Transmission method where data is transmitted it both directions, but only one direction at a time, Wi-Fi uses half-duplex data transmission
What is full-duplex data transmission?
Transmission method where data is transmitted in both directions simultaneously, used in telephones
What is the universal serial bus (USB)?
An industry standard used to transmit data
What is a USB port?
A socket which is part of a device or computer that enables a USB cable or USB device to be inserted
What is a USB cable?
A type of transmission media that uses the USB method to transmit data, can be used to connect devices
What is a USB connection?
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
What is a USB device?
A device that plugs into a USB port on a computer and transmits data using a USB connection
What are the advantages and disadvantages of the USB interface?
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
What is ethernet?
A type of connection that can be used to transmit data within a network
What are error detection methods?
Procedures used to detect errors in data so actions can be taken to correct them
What are some error detection methods?
Parity check, checksum, echo check, automatic repeat request (ARQ), check digit
What is a parity check and how does it work?
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
What is a checksum and how does it work?
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
What is an echo check?
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
What is an automatic repeat request and its ways of operating?
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
How does the positive acknowledgement method of an automatic repeat request (ARQ) work?
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
How does the negative acknowledgement method of an automatic repeat request (ARQ) work?
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
What is a check digit and how does it work?
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
What is encryption?
A method of securing data for storage or transmission that scrambles it and makes it meaningless
What is plain and cipher text, and how is the latter generated?
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
What are the two main methods of encryption?
Symmetric and asymmetric encryption
What is symmetric encryption?
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
How does asymmetric encryption work?
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
