Computer Science | The internet and the world wide web

Hello Future Computer Scientist! Understanding the Internet

Welcome to the most relevant chapter of modern computing: The Internet and the World Wide Web!
This section will help you understand how data travels globally, how your devices find information, and the essential rules (protocols) that make communication possible. Don't worry if this seems tricky at first; we will break down the entire global network into simple, manageable steps, using plenty of real-world examples!

Section 1: The Internet vs. The World Wide Web (WWW)

1.1 What is the Internet?

The Internet is the massive, global network of interconnected computer networks.
Think of it as the physical infrastructure: the cables, the routers, the satellites, and all the devices connected together. It’s the highway system for data.

1.2 What is the World Wide Web (WWW)?

The World Wide Web is the collection of documents (web pages) and other resources accessed via the Internet. It uses specific protocols (like HTTP) and addressing systems (like URLs).
Analogy: If the Internet is the library building and its wiring, the World Wide Web is the collection of books and resources inside the library.

Key Takeaway: The Internet is the hardware connection; the Web is the information (the content) accessed through that connection.

Section 2: How Data Travels – Packet Switching

2.1 What is Packet Switching?

When you send an email, load a video, or download a file, that large piece of data is not sent as one single chunk. It is broken down into small, manageable pieces called packets. This process is called packet switching.

Why do we use packets?

• Efficiency: Small packets can travel faster and take different, less congested routes.
• Error Management: If one packet is lost or corrupted, only that small piece needs to be resent, not the whole file.

2.2 The Journey of a Packet (Step-by-Step)

Imagine mailing a giant, fragile puzzle. You break it into 10 smaller, labeled boxes.

1. Segmentation: The data (e.g., a photo) is split into many small packets.
2. Addressing (The Header): Each packet is given a header. This header contains vital information:
   • The sender's IP address.
   • The recipient's IP address.
   • The total number of packets (e.g., "1 of 10").
   • The sequence number (e.g., "Packet 3").
3. Routing: Packets are sent across the Internet. Routers read the destination IP address on the header and decide the best path for that packet to travel. Different packets might take completely different routes!
4. Reassembly: Once all packets arrive at the destination computer, the data is checked using the sequence numbers (e.g., "1 of 10," "2 of 10," etc.) and reassembled into the original file. If a packet is missing, the recipient requests that specific packet be resent.

Section 3: Internet Addressing

For data to travel correctly, every device must have a unique address. There are several types of addresses used on the network.

3.1 IP Addresses (Internet Protocol Address)

An IP Address is a unique numerical label assigned to every device connected to a computer network that uses the Internet Protocol for communication.

Think of an IP address as your device's mailing address or phone number on the Internet.

• Format: They currently come in two main versions:
  • IPv4: Four numbers separated by dots (e.g., 192.168.1.1).
  • IPv6: A much longer alphanumeric address needed because we ran out of IPv4 addresses!
• Dynamic vs. Static IP: Most home devices get a Dynamic IP (it changes sometimes). Servers and crucial network equipment use a Static IP (it never changes).

3.2 MAC Addresses (Media Access Control Address)

The MAC Address is a unique identifier hard-coded into the hardware (specifically the network interface card, or NIC) of your device by the manufacturer.

Think of a MAC address as the physical serial number of your network card. It operates at a local level (LAN) and does not change.

Did you know? While IP addresses change when you move networks (like taking your laptop from home to school), the MAC address stays the same forever.

3.3 URLs and DNS (The Internet Phonebook)

Uniform Resource Locator (URL)

A URL is the human-readable address you type into your browser (e.g., https://www.google.com). People find URLs easy to remember, but computers only understand numbers (IP addresses). This is where the DNS comes in.

Domain Name System (DNS)

The DNS acts as the Internet's directory or phonebook.

The DNS Process:

1. You type the URL www.example.com into your browser.
2. Your computer sends a request to a DNS server (like looking up a name in a phonebook).
3. The DNS server looks up the domain name and returns the corresponding IP Address (e.g., 104.28.14.99).
4. Your computer now uses that IP address to connect directly to the correct server.

Memory Aid: Domain Name System = The Internet's Directory or Name Searcher.

Section 4: Essential Network Protocols (The Rules)

A protocol is simply a set of agreed-upon rules or standards that allow different devices and systems to communicate with each other effectively. They are essential for every task on the internet.

4.1 Core Internet Protocols (TCP/IP)

The entire internet relies on a suite of protocols, primarily TCP/IP.

• IP (Internet Protocol): Deals with addressing and routing the packets (like the addressing on the envelopes).
• TCP (Transmission Control Protocol): Deals with ensuring the packets are delivered reliably, in the correct order, and that any lost packets are resent. TCP guarantees delivery.

4.2 Web Access Protocols

HTTP (HyperText Transfer Protocol)

HTTP is the protocol used to transfer web pages (hypertext documents) between a web server and a web client (your browser). It is the foundation of the WWW.

HTTPS (HyperText Transfer Protocol Secure)

HTTPS is the secure version of HTTP. It uses SSL/TLS encryption (Secure Sockets Layer / Transport Layer Security) to scramble the data transferred between your browser and the server.
Always look for HTTPS! If you see a padlock icon in the address bar, it means your connection is secure, which is vital for passwords and bank details.

4.3 File Transfer Protocol (FTP)

FTP is the protocol used specifically for transferring computer files between a client and a server on a network.
It is often used when web developers upload files to their website server.

4.4 Email Protocols

Sending and receiving emails requires three primary protocols:

1. SMTP (Simple Mail Transfer Protocol): Used to send emails from the client to the server, and between mail servers. SMTP sends the message out.
2. POP3 (Post Office Protocol version 3): Used to retrieve emails from the mail server. The main feature is that it typically downloads the email and deletes it from the server (it acts like a physical post box you empty).
3. IMAP (Internet Message Access Protocol): Used to retrieve emails. It leaves the email on the mail server. This means you can access the same email from multiple devices (e.g., phone, laptop, tablet).

Section 5: Cloud Computing

5.1 What is the Cloud?

Cloud computing is the delivery of computing services—including servers, storage, databases, networking, software, and analytics—over the Internet ("the cloud").
Basically, instead of storing everything on your own hard drive or running software locally, you access those resources hosted remotely on large servers owned by a third-party provider.

5.2 Key Cloud Services

You probably use the cloud every day!

• Cloud Storage: Storing files online (e.g., Google Drive, OneDrive, Dropbox).
• Cloud Software (SaaS - Software as a Service): Accessing applications via a web browser (e.g., online word processors, web-based email).
• Processing Power: Businesses using remote servers to run complex calculations without needing expensive local hardware.

5.3 Advantages of Using the Cloud

• Accessibility: Data can be accessed anywhere in the world, on any device, with an internet connection.
• Backup and Recovery: Data is backed up automatically by the provider, reducing the risk of data loss.
• Cost Efficiency: Users often pay only for the resources they use (subscription models).
• Scalability: Resources (storage, processing power) can be easily increased or decreased based on demand.

Key Takeaway: The cloud shifts the responsibility for hardware maintenance and software updates from the user to the service provider.

Chapter Summary: Key Concepts Review

To master this chapter, ensure you know the difference between:

• The Internet (physical network) and the WWW (content).
• How Packet Switching enables data transmission.
• The role of IP Addresses (numerical location) and DNS (translating names to numbers).
• The protocols for securing communication (HTTPS) and handling email (SMTP, POP3, IMAP).

Great job making it through this essential section! The better you understand these underlying rules, the better you understand how the digital world works. Keep reviewing those protocols!