Structure of the Internet (Edexcel GCSE Computer Science)

Structure of the Internet

What is the Internet?

• The Internet is a global network of networks

• 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 (1) 

• Inside your router is a modem which allows you to connect to your Internet Service Provider (ISP) via a telephone line or fibre optic

• The ISP is connected to a database called a Domain Name System (DNS) (2)

• This results in other routers also connecting together, forming a large interconnection of multiple networks

• Before sending, internet data is split in to packets, each packet contains a header with:

  • Receivers IP address (3)

  • Senders IP address (3)

• The principal high-speed data transmission routes between networks is called the internet backbone

1. What is a router?

• The router is responsible for forwarding data packets between different networks

• The router selects the best route for data packets to take

• The router connects networks together, local area networks (LAN) to the wider internet which is a type of wide area network (WAN)

• The router can manage and prioritise data traffic, which can help to keep connections stable

• The router will assign IP addresses to the devices on the network

2. What is a domain name system (DNS)?

• 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

3. What is an IP address?

• An IP (Internet Protocol) address is a unique identifier used when sending or receiving data packets over the Internet (WAN)

• IP addresses are dynamic, they can change

• A packet header contains the senders IP to make it possible to deliver data to the right device

• A packet header also contains the receivers IP, this is to ensure the receiver can send a message to confirm a packets arrival or send reply data

• A device connecting to a network will be given an IP address, if it moves to a different network then the IP address will change

IPv4

• Internet Protocol version 4 is represented as 4 blocks of denary numbers between 0 and 255, separated by full stops

• Each block is one byte (8 bits), each address is 4 bytes (32 bits)

• IPv4 provides over 4 billion unique addresses (2³²), however, with over 7 billion people and countless devices per person, a solution was needed

IPv6

• Internet Protocol version 6 is represented as 8 blocks of 4 hexadecimal digits, separated by colons

• Each block is 2 bytes (16 bits), each address is 16 bytes (128 bits)

• IPv6 could provide over one billion unique addresses for every person on the planet (2¹²⁸)