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Computer Science: Unit 2: Data Transmission: Part 1: Data Transmission, Error Checking
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- 1How do computers hold data?In binary form, using on/off switches.
- 2What does each signal represent? What can computers turn this binary data into?One bit of data
Computers can turn this binary data into a stream of on/off signals which can be transmitted which can be sent from one place to another. - 3What can signals be in the form of? and how do they travel? What are these known as?Electrical pulses - that travel down metal/copper cables
Pulses of light- that travel down a fiber-optic cable
Wireless signals- using radio frequency
Infrared- by radiation
These are known as transmission medium - 4What are transmission medium?The system that carries signals
- 5What is the definition of Data transmission?The movement of data (bits) between at least 2 digital devices.
- 6BandwidthThe amount of data that can be carried at one time
- 7Long-distance TransmissionWhen a computer sends a signal to another computer.
- 8Short-distance TransmissionWhen the different parts of a single computer sends signals to each other.
- 9Simplex Communications give an exampleCommunications that go one way only
eg: listening to the radio - 10Duplex Communications give an exampleCommunications that go both ways
eg: phone communications - 11Half-duplex Communications give exampleCommunications that go both ways, but each sides have to take turns
eg: a walkie talkie - 12What do cables do?Cables connect devices together and signals are sent along the cable
- 13What are the 3 main types of cables?Twisted pair cable
Coaxial cable
Fiber-optic cable - 14What are twisted pair cable, what are the signals sent as and what are the advantages and disadvantages?Two thin copper wires are twisted together. The signals are sent as electricity.
Adv. least expensive cable, flexible and easy to install
Dis. Can be effected by electrical interference and aren't suitable for long distance. - 15What are Coaxial cables, what are the signals sent as and what are the advantages and disadvantages?A thicker metal cable protected by a layer of insulation.The signals are sent as electricity.
Adv. resists electrical interference's
Dis. more expensive than twisted pair cable and isn't as flexible. - 16What are Fiber-optic cables, what are the signals sent as and what are the advantages and disadvantages?(most modern type of cable) This is a cable made of stands of transparent plastic wound together.
They transmit signals as pulses of light
Adv. unaffected by electrical interference, suitable for long-distance
Dis. somewhat expensive - 17What is Serial Transmission and what are the advantages and disadvantages?The 8 bits are sent one after another. It is used for long distance connections. Wireless is always serial.
adv. most reliable method, they are sent one after another and arrive in the same order as sent
dis. can take longer cause bits sent one at a time. - 18What is Parallel Transmission and what are the advantages and disadvantages?The 8 bits are sent down 8 different wires. They all arrive at the same time.
Used for short-distance
Adv. quicker as all go together
Dis. more risk of error eg: if wires are different lengths arrive at different times and is why only used short distances. - 19What is the speed of data measured in?Bits Per Second
bps - 20What is the Baud rate?Rate at which the signals change
- 21What is the Baseband?One signal (bit) is sent one at a time down a serial connection
- 22When can serial be faster than parallel?With higher bandwidths, more than 1 bit can be coded in a signal, increasing the bit rate.
- 23How do you calculate the bit rate of channel?bit rate of channel = baud rate * number of bits per signal
- 24What is Skew?The problem that signals in parallel cables travel at different speeds so they arrive at different times, jumbling the data
- 25What are Computer Data Ribbons (known as Parallel ATA cables) used for?used inside the computer to connect components and drives
use 8,16 or 32 bits sent down separate lines. - 26What does IC stand for?Integrated Circuits
- 27What are Integrated Circuits?known as a 'chip', an IC is made of a semiconductor material named silicon. The silicon layer assembles millions or billions of tiny resistors, transistors sending data in parallel. Its a collection of microscopic electronic circuits. Many of the ICs are stuck onto a board called a motherboard. They are linked by wired connections by parallel data buses.
- 28What is a Data bus?a short distance connection that transmits data inside the computer. Can be serial or parallel.
- 29BusTransmits data inside the computer
- 30What is a Parallel data bus and what are the advantages and disadvantages?used to connect the parts of the processor
adv. Parallel transmission is fast, so it makes the computer work fast
dis. Needs more wires so takes up very limited space inside the IC or the circuit board. - 31What are Peripherals? What are some examples? Where and how do they connect?are the devices connected to the computer
eg: mouse keyboard, screen
They must be connected to the central processor of the computer. Buses are used to connect the peripherals to the processor - 32What are the ways to join a peripheral to the processor? give the examplespermanent wiring eg: keyboard to laptop
a plug in cable eg: a monitor
a wireless connection eg: a wireless mouse
A bus is needed to complete the connection - 33Why is a serial bus mostly used to connect a peripheral to the processor?Peripherals are slower than the processor so a fast connection isn't important. A serial bus is mostly used as it is fast enough, less expensive and uses less room
- 34What does a USB stand for and what is it? What is a USB port?Universal Serial Bus
a common standard for connecting peripherals. The USB port is a socket where a USB cable can be plugged in. - 35What are Transmission Errors?Sometimes data isn't transmitted correctly. They can have serious effects because the data will be wrong. To reduce error, we put systems in to check data for errors when it's transmitted, detecting any errors and correcting them.
- 36What are some causes of Error in Transmission Errors?mistakes in preparing the data
failures of equipment or transmission medium*
external interference
synchronization issues
power surges
wear and tear on the cables or connectors* - 37What are the Types of Error/Effects in Transmission Errors?Some bits are lost from the data stream
Extra bits may be added to the data stream
2 bits might swap around - 38What is Transcription error?An error when copying data from one form to another
eg: typing it in - 39What is Transposition error?Two data items swap position
- 40What does ARQ stand for?Automatic Repeat ReQuest
- 41What is ARQ?The transmitter sends some data (called packet). When the receiver gets the data packet it checks for errors. If there is no errors, the receiver will send an acknowledgement. If the transmitter doesn't receive an acknowledgement it sends the data again. TIME OUT is when the transmitter stops trying to send packets (the time limit)
- 42What are some Error Checking Methods 4Parity bits
Check digits
Check sums
Automatic Repeat ReQuest (ARQ) - 43What do Parity bits used for?Used to spot errors in data. Cannot correct errors but if it finds an error it can ask for a repeat transmission.
- 44What is parity?a description of a number as odd or even
- 45What will parity spot?When a bit has been lost from the signal
When a bit has changed value
(turns to opposite parity) - 46How does parity work?Before the data is sent, the transmitter counts how many 1s there are in each byte. One bit is used as a parity bit. Sometimes the parity bit is part of the byte, sometimes its sent after. It can be odd or even parity. Both computers must agree which parity to use before transmission
- 47What errors will Parity bit not spot?When 2 bits have been lost
When 2 bits have swapped positions
(number of bits stays the same) - 48What is Check Digit?a single digit added to the end of a transmitted number. It's used to check errors. It is worked out from the denary values transmitted.
- 49How do you calculate Check Digit? simple wayAdd up all the digits in the number.
Divide by 10 and find the remainder (mod 10) remainder has to be a digit of 10
(some people use mod11) - 50What are the problems of Check Digit?can't identify transposition error
- 51What are other methods of calculating Check digit to avoid error? What is the advantages and disadvantages of these?The digits in different positions are multiplied by different values. Then the numbers are added together and then:
1. Luhn method- every second digit is multiplied by 2 and the total must be an exact multiple of 10
2. ISBN-10- every digit is multiplied by its position, the check digit is the total mod11.
Adv. can identify transposition errors
dis. are more complex= more time - 52How does Checksum work?The transmitter add up the total of a group of numbers and then sends the total along with the numbers.
The receiver works out the total and compares it to the transmitters total.
The 2 totals should match, if they don't the data has to be re-sent.
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- (Unit 2) Computer Science GCSE Fichas sobre Computer Science: Unit 2: Data Transmission: Part 1: Data Transmission, Error Checking, creado por HRYN red el 14/11/2019.
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