The Internet (OCR GCSE Computer Science)

What is the Internet?

• The Internet is a collection of networks spanning the whole world
• The Internet is the most well-known Wide Area Network (WAN)
• The Internet is used to provide connectivity and is different from the World Wide Web, which is the collection of webpages you access via a web browser

How does the Internet work?

• In your home, you have a router 
• Inside your router is a modem which allows you to connect to your Internet Service Provider (ISP) via a telephone line or fibre optic
• An ISP is connected to a database called a Domain Name System (DNS)
• This results in other routers also connecting together, forming a large interconnection of multiple networks
  • Servers
  • Other routers
  • Other LANs
  • These routers are also connected to
• All of these inter-connected networks are known as The Internet

What is a domain name system?

• The Domain Name System (DNS) can be thought of as the Internet's equivalent to a phone book
• It is essentially a directory of domain names and is used to translate human-readable domain names to the numeric  IP addresses that computers use
• When you type a URL into your browser, the DNS translates the domain name into its associated IP address so your computer can connect to the server hosting the website
• Without DNS, we would have to remember the IP address of every site we want to visit
• When a domain is newly registered, or a server changes its IP address, the DNS record for that domain needs to be updated in what's known as DNS propagation

How does DNS work?

1. URL Entry: The user enters the URL (web address) of a website into the web browser
2. DNS Query: The web browser sends a query to a DNS server (usually hosted by your ISP) to translate the URL into an IP address
3. DNS Resolver: The DNS resolver checks its cache to see if it has the IP address for the requested domain. If not, it sends the request to the DNS root servers
4. Root Server Query: The root server directs the resolver to a Top-Level Domain (TLD) server (like .com, .org) based on the extension of the URL
5. TLD Server Query: The TLD server then provides the resolver with the IP address of the domain's authoritative DNS server
6. Retrieve IP Address: DNS server responds with the IP address for the requested domain
7. Request the Web Page: The web browser sends an HTTP or HTTPS request to the IP address it received
8. Server Response: The server at the given IP address processes the request and sends back the data for the web page (HTML, CSS, JavaScript, etc.)
9. Render the Web Page: The web browser renders the received data into the web page that you see

What are web servers?

• Web servers are dedicated servers that store web pages/websites and other resources
• They have a dedicated IP address to ensure that users can access them 24/7
• The most common web servers in use are
• Hosting websites
• Dealing with client requests

What are clients?

• Clients are end-users who make requests of web servers
• For example, a client requests a webpage such as www.savemyexams.com
  • The user will request the website by typing in the URL into their web browser
  • The request will be sent to their local ISP DNS
  • The DNS will return the IP address of that URL: 104.18.1.107
  • The client machine will then send a GET request to the web server
  • Save My Exams webserver will then return the webpage/resource to the client's web browser
  • More details about this process are above under the heading of 'DNS'

What is hosting?

• Hosting is the storing of websites, files and other content on servers
• The servers need to be accessible by potentially thousands of users and they need to be available 24/7
• The servers must be reliable and secure from any form of attack
• The IP address for the server must remain the same so that users can access the website whenever they want
• Servers are set up with the single purpose of serving these files in this manner and in a safe and secure way

What is the cloud?

• The cloud is a collection of servers which are used to store data, applications and files over the internet
• There are a number of advantages and disadvantages to use ‘The Cloud’ or cloud storage

Advantages & disadvantages of the cloud

Advantages	Disadvantages
Content in the cloud can be accessed anytime and from anywhere	Accessing content and software is only possible when the user has an internet connection
Users can use any device to access their content	Expanding capacity can become expensive if using it across a business
Users have a large storage capacity available to them	Vulnerable to security threats such as data leaks and photo leaks
Low cost / free to set up and use	It is not thoroughly clear to users who is the owner of the data once it is uploaded to a cloud service
Responsibility for backups and security is with the cloud service provider
Users can easily collaborate

Summary of learning

Keyword	Definition
Internet	A collection of LANs connected together spanning the whole world (WAN)
LAN	A collection of computers connected in a small geographical area using its own hardware
WAN	A collection of LANs connected together
DNS	Domain Name System: A directory of domain names (URLs) and their corresponding IP addresses
URL	Uniform Resource Locator: The web address typed into a web browser
ISP	Internet Service Provider: the company that provides internet services to you