chapter 4 - digital communication // edexcel igcse ict (9-1)

advantages of wired connections

- cost: cables are cheap if purchasing for a small number of devices. - speed: faster than wireless. - stability: less affected by interference than wireless. - security: most secure.

advantages of wireless connections

- cost: no need to buy cables, however you may need a wireless access point for multiple connections. - safety: none (some may be worried about radiation). - portability: portable within signal range. - mess: tidy - maintenance: none

benefits of satellite communication

- due to the large number of satellites, the system is always available. - it cannot be affected by power shortages.

disadvantages of wired connections

- safety: risk of tripping over cables. - portability: not portable as limited by connecting cables. may need signal boosted if connection is longer than 100 meters. - mess: can look untidy if lots of cables are used. - maintenance: using ports and cables continuously over a long period of time may damage them.

satellite: GPS

- satellite communications are used for GPS. - navigation aids make use of GPS signals (which are sent from a network of 24 satellites orbiting the earth) to calculate the exact location of a device. - a view of only 4 satellites is required to calculate an accurate location, but usually a device will be within view of about 12 satellites.

disadvantages of satellite communication

- satellite signals do not pass through solid objects, so they will not work in areas with tall buildings or in tunnels. - signals can be affected by atmospheric weather conditions (such as heavy rain & snow).

disadvantages of LAN

- security measures are needed as it is more prone to attacks than a standalone computer. - additional hardware means that there is more that could go wrong. - access to data and peripherals can be slow depending on network traffic. - expensive: LANs require maintenance to ensure that software is up to date, upgrades and backups which can be costly.

disadvantages of wireless connection

- speed: slower than wired. - stability: affected by interference and obstacles. - security: less secure than wired connection because it is easier to intercept a wireless signal.

factors affecting speed and volume of data transfer: transfer method

- wireless methods work on limited numbers of frequencies. - copper cables carry more frequencies than wireless, so cabled methods can have more bandwidth available to them than wireless methods.

broadcast communication: digital radio

DAB (Digital Audio Broadcasting) is used in Europe and Asia Pacific. it is broadcasted in the same way as DVB but provides more radio stations and can carry text data (e.g. time, name of the station, details of music) that DAB receivers can display.

broadcast communication: digital television

DVB-T (Digital Video Broadcasting - Terrestrial) is a method of DVB where transmitters are based on earth. to receive broadcasts transmitted by DVB-T, viewers can use the same antenna that they use to receive analogue broadcasts. - HDTV is an example of DVB-T2.

types of wired connections and their uses

HDMI (digital video connections), S/PDIF (digital audio connections), minijack (personal headphones), USB (storage transfer), ethernet (networking).

types of networks

LAN, PAN, MAN, WAN

LAN

Local Area Network. it connects digital devices that are in a small geographical area (like a building or a group of buildings close to each other).

MAN

Metropolitan Area Network. it is a network that covers a larger geographic area such as a city or community; used to connect computers in libraries & government agencies etc.

PAN

Personal Area Network. it is a group of connected devices that are all near an individual user (e.g. smartwatch to phone that is already connected to a laptop or speaker). - devices in a PAN can be connected to each other directly or through an access point. - WPAN: Wireless Personal Area Network.

WAN

Wide Area Network. it is a network that spreads over a large geographical area. it is often used to connect different buildings owned by national and international businesses. the internet is an example of a WAN. - WANs often use connectivity provided by third-party telecommunications companies to link LANs together through the internet. - they have slower transfer speeds than LANs because of their wider reach.

copper cable

a cable that sends data using electrical signals, which are conducted through copper wires.

fibre optic cable

a cable that sends data using light signals.

Internet Service Provider (ISP)

a company that provides access to customers to the internet for a monthly fee.

how is video streamed?

all of the data doesn't need to be downloaded before playback can start. a portion of the video data is stored temporarily in an area of memory called buffer. data worth a few seconds in first downloaded, then more data is downloaded to fill up the buffer while those few seconds are playing.

buffer

an area of memory used to temporarily store data, especially when streaming video.

broadband networks

broadband networks provide fast access to the internet through a connection to an Internet Service Provider (ISP). they use the fibre optic cable or copper cable network.

wired connection

cables are used to communicate via a wired connection. they use electrical signals. - some are used for multiple purposes such as USB. - others only meet one particular need, such as ethernet.

satellite: television - how is a video signal broadcasted?

digital television is broadcasted by DVB (Digital Video Broadcasting) - an example of a DVB is a DVB-S. - a video signal from the broadcaster is transmitted using a large antenna on earth to the satellite, which then broadcasts the signal back to earth. an antenna on a satellite TV viewer will receive the signal and send it to a set-top box to be decoded and sends it to a TV.

what would happen if the latency is high?

if the bandwidth is adequate, the game will play smoothly. if the latency is high, the events in a game will lag and will not seem responsive to the player's commands. in live television, high latency will result in a delay between real-time events and the video being received for playback.

types of wired connections: ethernet

it allows users to connect to wired networks. as its technology develops, the speed at who'd data can be transferred between devices is improved. ethernet cables can be 100m long before the signals start to lose quality.

how can we avoid the buffer from becoming empty?

it can be avoided by downloading the data constantly into the buffer, filling it up at a rate faster than it is being emptied.

advantages of LAN

it can secure its devices with the use of firewalls, antivirus software and other security features to prevent unauthorised access. it allows users on the network to share resources such as printers and other peripherals.

wireless connections: bluetooth

it is a type of wireless connectivity that lets devices connect over short distances. it cannot carry as much data as wifi and need to be paired with each other. - they are used to transfer small files and connect devices (e.g. smartphones and laptops) to peripherals (earphones, keyboards, etc).

types of wired connections: USB

it is a very common connection type and has been through multiple revisions to allow faster data transfer speeds as digital devices become more complex in their features and functionality.

wireless connections: wifi

it is a wireless technology used to connect devices to a network. that network itself can be connected to the internet so that the devices connected to the wifi network can connect to it.

network

it is formed when two or more computers are connected

device-to-device communication (and examples)

it is the direct connection of devices to each other using wired or wireless methods. examples: wired, minijack (used for analogue audio signals in portable devices), USB, HDMI (to transmit video and audio data), bluetooth

wireless connection: near-field communication (NFC)

it uses close proximity RFID (Radio Frequency Identification) chips. NFC is used in smartphones, payments cards and travel cards.

factors affecting speed and volume of data transfer: interference

other electromagnetic signals can interfere with wired and wireless signals. - electromagnetic fields from wireless devices (routers, fridges & microwave ovens) cause interference.

satellite communication - uses

satellite transmit data to and recieve data from digital devices (which use antennae to receive the radio signals that satellites transmit). uses: GPS, television, telephone, military.

what are the ways in which digital devices communicate?

satellite, broadcast, wired, wireless

speed of data transfer and latency

speed of data transfer also depends on latency. latency is the delay in time that it takes to send data between devices.

latency

the amount of time it takes to send data between devices.

domain

the name used to identify a web server.

define bandwidth

the number of bits that carried by a connection in one second.

tethering

the process of connecting a host device (e.g. smartphone or tablet).that uses a mobile broadband connection with one or more devices to share the broadband connection. mobile phone network provides can enable or disable it as part of the service agreement.

how is speed affected by bandwidth?

the speed at which devices can transfer data depends on the bandwidth of the connection. a connection with a large bandwidth can carry a large amount of data. this is because a higher bandwidth means that more data can be transferred per second, making uploads and downloads faster. (purpose: multiplayer online gaming, high-definition video streaming).

factors affecting speed and volume of data transfer: distance

the strength of a wired or wireless signal is reduced as the distance that it has to travel is increased.

frequency

the waveband at which a radio signal is transmitted.

wireless connections: infra-red (IR)

these signals cannot carry much data and only have a short range. transmitters must have a clear line of sight to receivers to allow the signal to travel in a straight line without being blocked. these signals are also affected by sunlight. - used in remote control devices such as TV remotes.

wireless connections: 3G & 4G

they are sometimes referred to as mobile broadband. they are used to provide internet access to smartphones and tablets when a mobile signal is not available. G stands for 'generation'.

how can cabled connections be protected by interference?

they can be shielded by wrapping them in a thin layer of metal.

mobile broadband networks

they provide high-speed wireless connectivity using 3G or 4G technology to connect to the mobile phone network, which acts as the user's ISP.

the 4 factors that affect data speed and volume of data transfer

transfer method (wired or wireless), interference, blockages, distance.

broadcast communication: analogue television & radio

transmitters broadcast television and radio signals that are received by a viewer's antenna, which sends a signal through a wire to the television or radio receiver, which converts it into images and audio.

factors affecting speed and volume of data transfer: blockages

walls and furniture reduce the strength of wireless signals, which reduces the available bandwidth.

types of wireless connections

wifi, bluetooth, 3G & 4G, infra-red (IR), near-field communication (NFC).

how can latency be identified?

you can 'ping' a domain to identify latency. pinging a domain sends a packet of data to a server, which immediately sends it back to the originating device - this is the 'ping time', which is the amount of time that it takes for the packet of data to make its return trip back to the originating device.