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3k Cellular and Satellite phones
Descripción
A level, A2 (Chapter 3) IT Mapa Mental sobre 3k Cellular and Satellite phones, creado por Gladys Mba el 09/03/2017.
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ict
it
ocr
g063
alevel
chapter 3
a2
it
chapter 3
a level, a2
Mapa Mental por
Gladys Mba
, actualizado hace más de 1 año
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Gladys Mba
hace más de 7 años
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Resumen del Recurso
3k Cellular and Satellite phones
Cellular Phones
How it works
Mobile -> Landline
Caller dials number
Request sent to BST by microwaves
Request passed to MSC
MSC checks status of caller e.g. if there is credit to make the call, if dialled number is allowed (e.g. international numbers)
Call connected to PSTN and frequency for call allocated.
Receiving call
MSC receive request to call a number
MSC identifies which BSC the mobile is connected to
Request passed to BSC
Request to dail number broadcasted by all BST under the BSC
Mobile Phone receive requests. Call is connected
Moving Phone
Database stores all cell locations of moibles
Phone registers with new cell as it moves, database is update
If area is covered by 2 cell, phone registers with the strongest signal
Applications
Business, social, or emergencies.
Phone and video calls
SMS (text) and MMS (sound/video/image) messages
WWw
Email
Smart Phones with apps, such as music players, or games
Country is broken in regions called cells
Infrastructure
Mobile stations (MS) such as a mobile phone
Base Station Transceivers (BST) for each cell. e.g. mobile phone mast- Gives signal coverage to cell
Base Station Controller (BSC)- Manages communication between BSTs and a MSC
Mobile Switching Centre (MSC)- Controls all calls taking place on a telephone network
Public Switched Telephone Network (PSTN)- Transfers calls from one phone company to another
Advatanges
O- User isn't restricted to one place
O- Can be used to summon help in emergencies
O- Can be used for other activities due to apps
O- Text messages can be used by people with hearing/speaking impairments
O- can access the WWW
Disadvantages
X- Battery runs out
X- Weak signals makes conversations break or can't make conversation
X- Cyber bullying
X- Texting and driving can cause accidents
X- Can disturb events, such as films
Satellite Phones
How it works
Connects directly to satellites orbiting earth rather than land-based BST
Low earth orbit (LEO)
e.g. iridium
Many satellites at 900 km altitude
Orbit earth 2 times an hour to offer global coverage
Obstacles overcome as next satellite moves into line of sight
Geosynchronous Earth Orbit (GEO)
e.g Thuraya
A few satellites orbit at 35,000 km
X- latency in calls due to long distance
Satellites remain in fixed position above earth
X- Obstacles can prevent calls in certain locations
Making phone call
Number dialled from satellite phone
Request transmitted by microwaves to satellite in space
Request passed to other satellite using different frequency until it can be sent to correct satellite receiver on earth
Call connected through PSTN
Signal bounced back to satellite if call is to another satellite phone.
Applications
Advantage
Communication in remote areas/ countryside/ ships/ mountains
Less likely to get tapped as it doesn't go through PSTN
used by military
O- Global coverage
O- Now as small a mobile phones
O- Can be used when mobile phone system is unavailable.
Disadvantage
X- Expensive phone and call rate
X- limited battery life, hinders long expedition
X- Requires line of sight
X- Limited data transfer rates
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