1.3.4 The Internet as a Collection of Networks

The internet is a worldwide collection of interconnected computer networks. Rather than being one single network owned by one organisation, it is made up of many smaller networks connected together so that devices on different networks can communicate.

Data may travel across several different networks before reaching its destination. Devices communicating over the internet use IP addresses so that data can be sent to the correct destination.

For example, a web server that hosts a website has an IP address that can be used to locate it. However, numerical IP addresses are difficult for people to remember, so websites are normally accessed using more memorable text-based addresses.

A URL (Uniform Resource Locator) is the address used to locate a resource on the web. It usually contains a domain name, which identifies the website or domain being accessed. For example, in “https://www.example.org/page”, example.org is the domain name, while https://www.example.org/page is the complete URL.

Although people use the URL, the computer still needs the corresponding IP address of the web server before it can make contact. Finding this IP address is the role of DNS.

The Domain Name Service (DNS) is made up of multiple Domain Name Servers that work together to match domain names to their corresponding IP addresses. This allows users to enter memorable domain names such as www.example.org instead of needing to remember numerical IP addresses.

The Domain Name Service works as follows:

1. When a user enters a URL into a browser, the device needs to find the IP address associated with its domain name. A request is sent to a Domain Name Server.
2. If that server has the required record, it returns the matching IP address. If it does not, other Domain Name Servers can be queried until the correct address is found.
3. Once the IP address has been returned to the user's device, the browser can contact the appropriate web server and request the required webpage or other resource.
4. If no matching IP address can be found, the requested website cannot be located and an error may be returned.

Hosting is the provision of internet-connected server resources so that data, services or applications can be made available to users over the internet. A company that provides these facilities is known as a hosting provider.

Hosting companies operate servers, often within large data centres, that remain connected to the internet so users can access the hosted content when required. Different types of hosting may be used for different purposes, such as:

• hosting websites;
• storing files;
• providing email services;
• hosting online applications;
• running game or media services.

Hosting providers may charge customers for server space, storage, bandwidth or other services, although some services may provide limited capacity free of charge.

A web server is a computer connected to the internet that stores website files and provides web content when it is requested. The user's device acts as a client. The web browser requests resources from the web server, and the server sends the requested resources back.

Web browsers and web servers communicate using protocols such as HTTP or HTTPS. These protocols are explored in Lesson 1.3.7 Network Protocols. The server processes the request and sends the required webpage files or other web resources back to the client, where the browser displays them to the user.

This follows the client-server model explored in Lesson 1.3.2 Network Types; the browser requests a resource and the web server provides it.

Website owners can operate their own web servers, but many use a web hosting provider instead. The hosting provider stores the website files on its servers and keeps those servers connected to the internet so that visitors can access the site.

Cloud computing means using storage, applications or processing resources provided by remote servers and accessed over the internet, rather than relying only on resources stored locally on the user's device.

The cloud is not one single place. Cloud services run on networks of servers located in data centres, and users may not know the physical location of the server storing or processing their data.

Cloud services can provide:

• storage, such as storing and synchronising files;
• applications, which can be accessed and used over the internet rather than being installed and run entirely on the user's local device;
• processing power, where remote servers perform computational work for the user.