OCR ICT G063 Chapter 3

• within locally defined area
• connected by cables owned by company
• able to share local peripherals

• geographically remote
• external telecommunications
• connected by third party cables

• smaller part of a LAN or WAN in which only specific machines can see each other 
• machines can be added or removed from the virtual network without rewiring them 

connect computers together using telecommunications system. TCP/IP protocol

• world wide communication network
• connected by high speed data channels e.g. leased line
• TCP/IP protocol
• open network
• services open to public
• world wide access

communication system that is restricted and internal to an organisation

• internal communication 
• based on company LAN or WAN
• TCP/IP protocol
• closed network
• authorised members only 
• access oly from within organisation

access to an organisation's intranet.

• external personnel access intranet
• mobile phone network or VPN to connect
• TCP/IP protocol
• closed network
• authorised users only
• world wide but private access to intranet

network of workstations connected to server 

• centralised anti-virus management takes onus away from user  
• usernames and passwords required to access network higher level of security can be managed and maintained 
• all client workstations managed centrally so applications deployed using server and no user involvement 
• require lots processing power, memory and hard disks - expensive
• server fails - no access to any network resources
• network manager required to maintain complex structure of server

no server - each computer is a peer of another

• less expensive since no need for server
• simpler to set up as it requires less technical knowledge
• no reliance upon central server - if syetm fails only shared resources on that computer will be lost
• backup not centralised - greater responsibility on individual
• if peer unavailable - access to peripherals on the peer is lost
• data can be stored on any computer - data difficult to find

measure of capability of of a communication channel to transfer data. measured in bits per second

bottleneck - smallest bandwidth between user and place data being downloaded from

importance:

• large data transfer when needed quickly
• accessing real time content
• quick downloads

cables: 

• cheaper than optical
• shielded - reduce electromagnetic interference - used in high speeds networks with higher bandwidth
• prone to electrical interference
• limited to 100m
• unshielded - data packets lost

optical:

• high bandwidths available
  
• no electrical interference
• little loss of data
• where 100m+ cable required
• expensive to install

wireless:

• not require cables
  
• prone to being weakened from walls and furnishings 
• less bandwidth available

switch: number of ports into which connect cables to direct traffic to destination

hub: enables communication between devices in a LAN 

network interface card: connects device to network. MAC address uniquely identifies a computer on a network

repeater: a device used to link two cable segements, extends the range of the network

bridge: connects together two LANs

wap: allows you to send and receive wireless signals

router: stores addresses of devices connected to it and sends data packets to recipient devices

gateway: exit from one network, entrance into another

firewall: prevent unauthorised access to or from a network

infrared:

• inexpensive
• requires little power - suitable for battery controlled devices
• require line of sight 
• work at short distances only (10m max.)
• low bandwidth

fibre optic:

• high security - less diffcult to tap into
• greater capacity - more data exchanged simultaneously
• low loss of signal and no electrical interference - better quality data transmission
• cable more expensive than wire media
• damage to cable - entire cable needs re-laying
• physical disruption if cable needs to be housed underground

laser: two laser devices in direct line of sight each sends a beam to the other and can receive from another.

• wide bandwidth compared to infrared
• set up quickly
• beams travel 100s miles
• only work in line of sight
• atmospheric conditions cause interference

bluetooth: enable devices with 10m to exchange data with each other

• uses small amount of power - ideal for battery operated devices
• no line of sight required
• max range 10m
• low bandwidth

wireless communication: no physical connection as data is transmitted by electro magnetic waves

• no need for cables to connect
• device can work anywhere within range of wap
• sufficient bandwidth for most internet use
• client details accessible non compliance with DPA
  
• require additional hardware raising cost of installation
• other electronic equipment can interfere with signal

email:

• requires username and password to access
• can be sent from anywhere in the world
• can be picked up anywhere

fax:

• can be picked up by anyone in the location
• sent from anywhere in the world
• sent to a specific location

video conferencing:

• requires all individuals to be present
• uses high bandwidth- real time communication
• see and hear the recipient

instant messaging: 

• real time two way communication
• users set status to offline or available
• informal collaborative chat

• keep in touch at long distances
• share photos, info and interests
• meet new people
• bullying
• loss of privacy
• fake profiles
• employers check social media profile before hiring

benefits to businesses:

• improved search engine ranks
• visitors share links to business site
• engage with customers

ADSL: a range of frquencies used on copper line to provide broadband connection to internet

• asymmetric
• copper cable to connect
• sufficeint bandwidth - handle large volumes of data
• handle simultaneous data and audio streaming
• requires user to be ceratin distance from telephone exchange
• electrical interference on copper cable
• large contention ratio - not able to use full bandwidth

ADSL: cable

• fibre optic links - higher bandwidths
• asymmetric
• low contention ratio

ADSL: wireless

• asymmetric
• requires 3G or better signal- enable video calls + high bandwidth 

Leased line: direct connection between an organisation and outside location

• symmetric
• no contention ratios - bandwidth is guaranteed
• high bandwidth
• very expensive 

Satellite:

• remote areas where physical or wireless connections not available
• relies upon microwaves
• low bandwidth - low volumes of data sent
• line of sight required - may be obstacles in way
• limited bandwidth speed - video image quality poor with pauses
• latency delay between transmitting and receiving data - make real time communication difficult

One way satellite: downloading but telephone line used for uploading

Two way satellite: allows downloading and uploading. asymmetric. 

• coverage: SP global coverage whereas MP rely on proximity to terrestail base station masts
• size: SP larger and heavier than MP
• security: SP more secure since they bypass local telecoms systems whereas cell phones monitored more easily

Mobile phone:

• used anywhere with signal
• summon help in emergencies
• access to info on WWW
• limited battery life
• weak/no signal

Satellite phone:

• global coverage - even in remote areas
  
• avoid conversations being monitored
• latency
• high cost of calls

Low earth orbit: (iridium) only a few hundred km above Earth

• close to the ground - see earth in great detail (used by weather forecasters and scientists)
• need little power to transmit data - cheaper to launch
• very little time delay in data being sent and received - ideal for real time communication
• need a lot of them to recieve constant coverage over one spot

iridium has 66 satellites orbiting earth so global coverage is always available since as one moves out of sight the next one comes into line of sight.

Geosynchronous earth orbit: (thuraya) 1000s km above Earth

• delays experienced
  
• obstacles prevent communication

thuraya has 3 satellites orbiting earth at altiude of 35000km. covers Europe, Africa, Middle east and Australia

Geostationary: travels at right speed to keep above the same spot on Earth at all times.

• can only support limited number of satellites otherwise they interfere with each other
• time delays

Weather:

• geostationary- fixed position follow line of equator
• polar orbiting- orbit between North and South few 100 km above earth= high quality pics
• monitor weather in real time
• monitor events - fires and hurricanes
• monitor indirect events e.g. energy usage
• expensive to launch and operate
• limited life span
• not always accurate
• 'space junk' is a serious hazard for further missions

GPS/Satellite tracking: 

• recieve signal from satellite, minimum 4 satellited required, satellite transmits location and time, receiver times differences between satellite signals to determine position
• finds quickest routes - avoid traffic and road works
• accuracy +/- 30cm
• availble at any time
• atmospheric conditions affect accuracy
• maps not up to date
• obstructions to signal e.g. tall buildings

Television:

• DBS: transponders receive original television signal, amplify it to high power and send to customers on earth.
• 100s channels from same box
• received in remote areas
• encryption allows tv companies to charge for specialist channels
• line of sight required
• hardware and installation expensive
• subscription fees expensive

GPS/Satellite tracking: 

• recieve signal from satellite, minimum 4 satellited required, satellite transmits location and time, receiver times differences between satellite signals to determine position
• finds quickest routes - avoid traffic and road works
• accuracy +/- 30cm
• availble at any time
• atmospheric conditions affect accuracy
• maps not up to date
• obstructions to signal e.g. tall buildings

Television:

• DBS: transponders receive original television signal, amplify it to high power and send to customers on earth.
• 100s channels from same box
• received in remote areas
• encryption allows tv companies to charge for specialist channels
• line of sight required
• hardware and installation expensive
• subscription fees expensive

a set of rules that allow devices to work together

importance:

• devices purchased from different manufacturers can work together
• performance level guaranteed no need to test
• allow competiton between manufacturers giving better value for money

a standard set of rules that govern the exchange of data

• determine rules both devices are to use to ensure communication occurs without error
• detect and correct errors ensure mistakes do not have impact
• define how data transferred via an internationally agreed standard