Computers can be linked together to share resources or communicate with other users. A group of linked computers is called a network. Computer networks can be small or large and extend over a small area or a large area. If you had a couple of computers at home, you could link them together. A college or training centre might have their computers linked together. A local area network (LAN) is the name given to a network that extends over a limited area like a training centre, college or office building. A wide area network (WAN) is the name given to, funnily enough, a network that extends over a wide geographical area. A company based in several locations will have their computers linked together in a WAN. Here's a simplified WAN made up of 4 different LANs
This wide area network is composed of four local area networks. In the local area network, the computers are linked to each other. In the wide area network, the local area networks are connected to each other. The individual Local Area Networks might be in Tipperary/Laois/Kilkenny/Waterford or Ireland/Scotland/Belgium/Spain. Wide area networks don't need to be in the same country, or even the same continent.
There are a variety of ways to link computers. These are the most common
- Bluetooth - for very small LANs where devices are close together, Bluetooth can be used. Bluetooth is a wireless technology standard that uses ultra-high frequency (UHF) radio waves to exchange information between devices. Bluetooth isn't very powerful, so the devices need to be near each other
- Ethernet - Ethernet cables look like thick telephone cables. They connect computers to boxes called hubs or switches which send information in the form of electrical signals from computer to computer.
- Optical Fibre - like Ethernet, optical fibre cables connect computers to hubs and switches. Optical fibres transmit light rather than electricity and can transfer information much faster than Ethernet cables.
- WiFi - WiFi, like Bluetooth, uses radio waves to exchange information between devices. The radio waves used called S band and C band and are much more powerful than Bluetooth's UHF, hence WiFi networks don't need devices to be close to each other.
Networks can be closed or open - they can have connections to other networks. A college or training centre might have a network (a LAN) that connects together all of the computers in that location. That network might be connected to other sites through a WAN. The WAN might then be connected to the Internet.
Client/Server and Peer to Peer
In some networks, all devices are connected to a server, a computer that performs services (server - services) for other computers on the network. The server might store a lot of information that will used by other computers in the network. This type of network is called a client/server network. The computers that use the server all called clients.
In other networks all the computers might store information accessed by other computers, this is called a peer-to-peer network. Most networks however operate on the client/server model.
The Internet is a super-network - a network of networks, which consists of a worldwide network of computer networks joined together and communicating and sharing information using a series of standardised methods and rules. The Internet originated in work done for the US Department of Defence in the 1960s on the sharing of information between different computers. It's grown a little since then.
The World-Wide Web, or just the web is usually what we mean when we say "The Internet", but the web is only part of the Internet. The World-Wide Web is a collection of documents, images, videos, apps and other resources accessed through apps called "web browsers" or simply "browsers" which are discussed on another page. Information on the World-Wide Web is accessed using a set of rules for communicating between computers called the Hypertext Transfer Protocol. All you need to know though is that the Internet is more than the web!
A set of rules called the Internet Protocol (IP) controls how computers communicate with each other and transfer information across the Internet.
Email (again, discussed on another page) is an important communications service available via the Internet, which allows the sending of documents, images and other file types as attachments.
File sharing is another use of the Internet. It's fairly easy to send transfer large amounts of data across the Internet. Files can be sent directly via email, transferred from one device to another using a standard called "File Transfer Protocol (FTP)" or stored in the "the cloud" and can be accessed using a web browser or by dedicated apps.
An intranet is a computer network for sharing information, documents, collaboration tool and computing services within an organisation, usually inaccessible to anyone outside of the organisation. An intranet is like a private version of the Internet (intra = within, inter = between) and uses the same standards and rules as the Internet.
Each computer in a network has an IP address to identify it. IP stands for Internet Protocol, which is the standard or set of rules for governing how information is communicated across computer networks. Every computer's IP address is unique and can be thought of as the equivalent of a house address (or Eircode!) or telephone number. In version four of the Internet Protocol (IPv4), an IP address consists of four numbers separated by full-stops. This site's IP address is 63.32.285.201
The individual numbers can go from 0 to 255. This means there are potentially 256 x 256 x 256 x 256 unique IP addresses which is nearly 4.3 billion addresses. Because some number are reserved for special purposes (like Intranets and home networks), there's fewer than that available, and as the number of computers connected to the Internet continues to grow, the numbers will all be used up.
To address this, a new IP address system is being put in place - called Internet Protocol 6 (IPv6). IPv6 addresses use numbers and letters, for example 2001:0db8:0001:0000:0000:0ab9:C0A8:0102 IPv6 has 340,282,366,920,938,463,463,374,607,431,768,211,456 different addresses. Like IPv4, some of these will be reserved for special purposes, but otherwise should last for a while.
- Image: LAN/WAN https://upload.wikimedia.org/wikipedia/commons/7/72/Wan1.jpg Attribution: Mdnz27 / CC BY-SA 4.0