3.5.1 Computer Networks

• When two or more computers/devices are connected together through a communication medium, allowing them to exchange data, share resources and communicate, we have a computer network.
• Often a computer network conforms to the server / client model.
• Examples of networks could include:
  • Mobile Phones/Devices using Bluetooth (PAN).
  • Bourne Grammar School using wired or wireless (LAN).
  • The Internet (WAN).

• The largest and most famous Wide Area Network (WAN) in the World is the Internet. This is a collection of inter-connected networks (LANs).
• The Internet is a Worldwide collection of computers/devices and networks, not owned or managed by any one group of people. Anyone can access the Internet using either wired or wireless connections.
• The World Wide Web (WWW) - Is a collection of html documents and web pages that are all linked to each other using hyperlinks. Sir Tim Berners-Lee invented the WWW in 1989.
• Websites are stored on web servers connected to the Internet, and each website has a unique web address (IP Address), so that it can be accessed. All information on the WWW is stored as HTML documents known as web pages.
• Web Pages can be accessed using a program called a Web Browser such as Google Chrome, Firefox or Safari.

• Let's define some of those terms:
  • Communication Media refers to the connection between computers. This could be standard copper cable (normally Cat5e or 6), Fibre Optic cable or Wireless Radio.
  • Resources are devices such as printers or storage devices, that computers on the network have shared access to.
  • Servers are just another computer. They may sometimes be very high-powered if the service they are providing is computationally hard (such as serving millions of web-pages or performing advanced modelling) or they can be tiny devices such as a Raspberry Pi (serving media over a home network).
  • Clients are computers that use the services provided by the server.

• Computer networks allows computers and devices to be connected together to share data. This includes:
  • Computer to computer communications.
  • Computers communicating with devices such as printers, a mouse and a keyboard.
  • Mobile phone networks.
  • Smart Devices (Televisions, Digital Assistants, Fridges, iKettles, iToasters, wearable tech, Smart Home Devices etc..)
  • Tablets amd media players downloading/streaming videos and music and playing them through external devices such as speakers and digital projectors.

Personal Area Networks (PANs)

Local Area Networks (LANs)

Wide Area Networks (WANs)

In order to connect to a network, a computer device needs some hardware and also software that allows it to communicate with each other.

• A Network Interface Card (NIC) is a component that connects a device to a network. It formats the data sent into the required format according to the protocols (rules) of the network. NICs can exist for both wired and wireless connections.

• Switch – Switches connect devices on a LAN. Switches receive data (in units called frames) from one device and transmit this data to the device on the network with the correct MAC address. They build up a table of MAC addresses on the network.

• Routers – Are responsible for transmitting data between networks – They’re always connected to at least two different networks. Routers have a crucial role on the Internet, directing data (in units called packets) to their destination. They are used in homes and offices to connect the LAN to the Internet.

• MAC Address (Media Access Control) – Every device needs a unique identifier so that it can be found on a network that allow data to be sent to the correct component. They are unique to the device and cannot be changed. MAC addresses are 48 bits in length and are usually displayed as a 12-digit hexadecimal number.

In order for a network to communicate, it requires a form of transmission media. The two ways that network devices communicate over a network are either by cable or radio waves (Wired or Wireless).

• Ethernet Cables – The most common Ethernet cables are CAT5e and CAT6, they containing four pairs of copper wires that are twisted together to reduce internal interference. Data is sent as electrical currents.
• Fibre Optic Cables - Uses glass (or plastic) threads (fibres) to transmit data. A fibre optic cable consists of a bundle of glass threads, each of which is capable of transmitting messages modulated onto light waves. Pulses of light are generated by a light emitting diode (LED) or a laser.

• Wireless (Wi-Fi) Wireless Fidelity – Like mobile phones and TVs, wireless networks use radio waves to transmit data. Microwaves are a type of radiowave that consist of electromagnetic radiation travelling in waves with a frequency higher that 1 gigahertz (1GHz to 300GHz per second). Data is transmitted across the network in frequency bands of between 2.4 and 5GHz.
• The bands are split into numbered channels that each cover a small frequency range. They also use different Wi-Fi spectrums for example; 802.11b, 802.11g and 802.11n.

• There are many different ways of configuring hardware on a computer network. The two main topologies are
  • Bus

• Star