3c. Networks and Communications Flashcards
Name 5 types of broadband connection
ADSL, cable, wireless, leased line, satellite
What does ADSL stand for?
Asymmetric digital subscriber line
Describe an ADSL connection
When a range of frequencies are used on an existing copper telephone line to provide a broadband connection to the internet. More frequencies are allocated to downstream bandwidth as it is used more for downloading. Can use telephone line at same time. Local AM radio stations can cause interference. Used mainly in homes.
What is a cable internet connection?
Uses fibre optic. Can be provided by cable television companies.
Describe wireless internet connection.
Since 3G, it has become more popular. Enables users to be able to connect to the internet whilst not at home.
What is a leased line connection?
Exists between two locations as direct connection. They must be installed especially, so expensive. Symmetric stream.
What does symmetric mean?
Same amount of upstream bandwidth as downstream bandwidth.
What is one way satellite broadband?
Uses a satellite connection for downloading data from the internet, but uses a modem and telephone line for uploading data.
What is two way satellite broadband?
Allows both downloading and uploading through the satellite connection. Asymmetric as downstream has a higher bandwidth than upstream.
A cellular telephone network consists of a number of components that enable mobile communication to take place, such as:
Mobile stations (a mobile phone), a mobile phone mast, a mobile switching center, a base station controller and a public switched telephone network.
What is a mobile switching center?
This controls all the calls taking place on the mobile phone network.
What is a base station controller?
This manages the communication between Base Station Transceivers (a mobile phone mast) and the mobile switching center.
What is a public switched telephone network?
When a call is being made from one phone company to another mobile phone company or to a landline, it needs to go through the PSTN.
When a phone call is placed from a mobile phone to a landline phone, a number of actions take place, such as:
- The caller dials the landline number from the mobile phone 2. A call request is sent by microwaves to the base station transceiver for the cell the mobile phone is currently connected to. 3. This request is passed to the Mobile Switching Center 4. The MSC checks the callers status (if there is enough credit, if the number dialled is allowed) 5. The MSC then connects the call through the public switched telephone network and allocates a frequency to the mobile station (the phone).
When a phone call is made to a mobile phone, the following actions take place:
- The MSC receives a request for a call to a mobile phone number. 2. The MSC identifies within its actives database which BSC the phone is connected to. 3. The request is passed to that BSC. 4. The request to dial the number is then broadcast through all the BSTs under the control of the BSC. 5. The mobile phone being called receives the request and tells the BST. 6. The call is then connected by the MSC using a frequency allocated to voice calls.
What is a satellite phone?
Looks similar to a mobile, but connects to satellites orbiting the earth instead of land based station transceivers. THey cover the whole glove.
What are the two types of satellite’s for satellite phones?
Low Earth orbit and Geosynchronous earth orbit.
What is a low earth orbit satellite?
Orbit Earth approximately twice every hour, so global coverage is always available.
What is a geosynchronous earth orbit?
35,000km above earth. There is a latency (delay) in calls. They remain in a fixed position.
What can satellite phones do?
Communicate in remote areas (expeditions in the Antarctic or at sea), after natural disasters where the phone network may be unavailable, communication by people who want to avoid their calls being tapped.
What is GPS used for commonly?
Sat nav in cars.
How does GPS work?
24 Satellites in orbit. Each orbits Earth twice a day - always at least 4 in line of sight. A GPS receiver will look for communication from at least three satellites and use a method called ‘trilateration’ to calculate the distance to each satellite.
How is a weather satellite used?
Can monitor weather patterns across the globe. Most commonly used to view photographs taken of cloud formations which can then predict the weather.
How do weather satellites work?
Either in geostationary orbit (fixed position above the equator) or polar orbiting. 850km above earth.
