Computer networks

• a group or system of interconnected people or things.
  Oxford Dictionary

• Pair up with someone in the class and think about the video you have just seen.

• Think of three points that you have learned from this video. 

• Unfortunately, not everyone understands what the Internet is...

Examples of networks include:

• The school network

• Your home network

• Government networks

• Company networks

• Networks can become very, very large. For example, the Internet is one of the largest networks serving almost 4.4 billion users as of 2019.

• To be able to cope with this, rather than having a connection to each person’s individual computer, we use many smaller networks.

• For instance, in your home you will probably have a small WiFi network that allows you to connect to the Internet.

• Computers that are not on an network are called stand alone computers.

• Computer networks are made up of multiple computers which all communicate using agreed protocols.

• Each computer is given an IP address that allows the computer to uniquely identify itself.

There are two main type of network:

• Local Area Network (LAN) - E.g. your home network or the school network

• Wide Area Network (WAN) - E.g. The Internet

• A LAN covers a small area such as a single room or a building and is usually owned by an individual or single company.
• The school has a LAN that connects all of the computers within it together and on to a bigger network.

• A WAN covers a much larger area than a LAN. For example, a WAN may cover a whole country (e.g. BT or Sky Broadband) or a whole continent.
• The Internet is an example of a WAN.
• WANs are often made up of smaller LANs.

• There are two major formats of transmission media used to carry data:
  1. Wired (using a cable)
  2. Wireless (e.g. WiFi)
• We talk about bandwidth being the amount of data which can be carried over a transmission medium at the one time.
  

• Wired networks can be wired together using different cabling, ranging from standard copper cables to more advanced optical fibre cables.

• Allows sharing of data and files
• Allows access to data and files anywhere on the network
• Allows the sharing of devices such as printers (and saves money)
• Allows for easy communication between users
• Data can be easily backed up
• Allows files to be stored in one secure location and only accessed on request
  

• Cost – setting up a network can be expensive
  Managing a network can be difficult, especially as they get bigger.
• If the network goes down, all users may end up suffering the consequences and may not be able to access their files.
• Risk of hacking. Files on a network can be accessed remotely and if not secured correctly they could be stolen by a hacker.
  

Advantages of LANs:

• Allows sharing of expensive hardware
• Allows fast transmission of files
• Allows for reliable transfer of files
• Allows computers to share one Internet connection

Advantages of WANs:

• Allows data and files to be shared around the world
• Allows users to remotely access their computers
• Allows services such as ATMs (cash machines) to be connected directly to the bank’s network and accessed anywhere
• Allows companies who are in different countries or continents to communicate as if they were in the same building

The stages for sending data from one computer to another are:

• Data is requested from the host computer (sender) by the user’s computer (receiver). The receiver tells the sender what it wants and tells the sender it’s IP address.

• The sender packages the data into chunks or packets with the receiver’s IP address on them and sends them to the receiver at their IP address.

• The receiver waits for the packets from the sender and rebuilds the data into the file

• Firewalls are one of the most important forms of network security. A firewall checks incoming (and outgoing) packets before allowing them in or out of the network.
  They check that the packets are following a set of rules. They are also used to set rules about which application or system should receive the packets.

• Rules are created that take account of the following:

  • sender (source) IP address

  • receiver (destination) IP

  • address

  • port numbers

  • protocols