3c. Networks and Communications

Question 1

Name 5 types of broadband connection

Answer 1

ADSL, cable, wireless, leased line, satellite

Question 2

What does ADSL stand for?

Answer 2

Asymmetric digital subscriber line

Question 3

Describe an ADSL connection

Answer 3

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.

Question 4

What is a cable internet connection?

Answer 4

Uses fibre optic. Can be provided by cable television companies.

Question 5

Describe wireless internet connection.

Answer 5

Since 3G, it has become more popular. Enables users to be able to connect to the internet whilst not at home.

Question 6

What is a leased line connection?

Answer 6

Exists between two locations as direct connection. They must be installed especially, so expensive. Symmetric stream.

Question 7

What does symmetric mean?

Answer 7

Same amount of upstream bandwidth as downstream bandwidth.

Question 8

What is one way satellite broadband?

Answer 8

Uses a satellite connection for downloading data from the internet, but uses a modem and telephone line for uploading data.

Question 9

What is two way satellite broadband?

Answer 9

Allows both downloading and uploading through the satellite connection. Asymmetric as downstream has a higher bandwidth than upstream.

Question 10

A cellular telephone network consists of a number of components that enable mobile communication to take place, such as:

Answer 10

Mobile stations (a mobile phone), a mobile phone mast, a mobile switching center, a base station controller and a public switched telephone network.

Question 11

What is a mobile switching center?

Answer 11

This controls all the calls taking place on the mobile phone network.

Question 12

What is a base station controller?

Answer 12

This manages the communication between Base Station Transceivers (a mobile phone mast) and the mobile switching center.

Question 13

What is a public switched telephone network?

Answer 13

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.

Question 14

When a phone call is placed from a mobile phone to a landline phone, a number of actions take place, such as:

Answer 14

1. 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).

Question 15

When a phone call is made to a mobile phone, the following actions take place:

Answer 15

1. 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.

Question 16

What is a satellite phone?

Answer 16

Looks similar to a mobile, but connects to satellites orbiting the earth instead of land based station transceivers. THey cover the whole glove.

Question 17

What are the two types of satellite’s for satellite phones?

Answer 17

Low Earth orbit and Geosynchronous earth orbit.

Question 18

What is a low earth orbit satellite?

Answer 18

Orbit Earth approximately twice every hour, so global coverage is always available.

Question 19

What is a geosynchronous earth orbit?

Answer 19

35,000km above earth. There is a latency (delay) in calls. They remain in a fixed position.

Question 20

What can satellite phones do?

Answer 20

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.

Question 21

What is GPS used for commonly?

Answer 21

Sat nav in cars.

Question 22

How does GPS work?

Answer 22

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.

Question 23

How is a weather satellite used?

Answer 23

Can monitor weather patterns across the globe. Most commonly used to view photographs taken of cloud formations which can then predict the weather.

Question 24

How do weather satellites work?

Answer 24

Either in geostationary orbit (fixed position above the equator) or polar orbiting. 850km above earth.

Question 25

How is satellite television used?

Answer 25

Lets viewers watch more channels than available through aerial. Sky uses the Astra satellite system.

Question 26

What are free to air channels?

Answer 26

Do not require a subscription and so can be viewed by anybody who has a satellite dish and set top box.

Question 27

What does TCP/IP stand for?

Answer 27

Transmission control protocol/internet protocol. It defines how signals are sent across the internet and enables internet users to communicate with each other.

Question 28

What is SMTP?

Answer 28

Simple mail transfer protocol. This governs the sending of emails so that a device will be able to send successfully an email to another device.

Question 29

What is PPP?

Answer 29

Point to point protocol. This sets standards for how two computers that are connected directly to each other should communicate.