What is the Internet?
The Internet is a vast, decentralized network of interconnected devices that communicate using a common set of rules called protocols. It enables information exchange through websites, emails, file transfers, and more.
How Does the Internet Work?
- Devices (computers, smartphones, IoT) connect via an Internet Service Provider (ISP).
- Data travels in packets through routers and networks.
- Each device has a unique IP address for identification.
- Protocols like HTTP, DNS, and TCP/IP govern communication.
Example: When you search for something on Google, your request is broken into packets, sent through multiple routers, processed by Google’s servers, and the response packets return to you.
Network Edge: End Systems, Access Networks, and Links
The network edge refers to devices and connections that allow users to access the Internet.
End Systems (Hosts)
These are devices connected to the Internet:
- Computers, smartphones, IoT devices
- Identified by unique IP addresses
- Communicate using protocols (HTTP, FTP, SMTP, etc.)
Access Networks
The network that connects end systems to the Internet:
- Wired (DSL, Fiber Optics, Ethernet) – Faster, reliable
- Wireless (Wi-Fi, Cellular 4G/5G, Satellite) – More flexible
Example: Your mobile data (5G) or home broadband (Fiber) is your access network.
Links
The physical connections that carry data:
- Fiber-optic cables (fast, long-distance communication)
- Copper cables (Ethernet) (local area networks)
- Wireless signals (Wi-Fi, Bluetooth, Satellite)
Network Core: Packet Switching, Circuit Switching, and Network Structure
The network core is the backbone of the Internet that enables efficient data transfer.
Packet Switching vs. Circuit Switching
| Feature | Packet Switching | Circuit Switching |
| Method | Data is broken into packets | Dedicated path is reserved |
| Efficiency | More efficient, used in the Internet | Less efficient, used in telephony |
| Example | Email, web browsing | Traditional telephone calls |
Example: The Internet uses packet switching, where messages are divided into packets and sent independently. In contrast, a telephone call uses circuit switching, where a dedicated line is established.
Network Structure
The Internet follows a hierarchical structure with different levels of Internet Service Providers (ISPs):
- Tier-1 ISPs – Global providers (e.g., AT&T, Tata Communications)
- Tier-2 ISPs – Regional providers connecting Tier-1 and local ISPs
- Tier-3 ISPs – Local providers offering home/business connections
Delay, Loss, and Throughput in Networks
Types of Delays
- Processing Delay – Time to examine packet headers at routers.
- Queuing Delay – Time packets wait in a queue before forwarding.
- Transmission Delay – Time taken to push a packet onto the link.
- Propagation Delay – Time taken for a packet to travel physically.
Example: A slow website load might be due to high queuing delay at a busy router.
Packet Loss
Occurs when packets are dropped due to congestion or errors, requiring retransmission.
Example: During video calls, lost packets cause buffering or glitches.
Throughput
The rate at which data is successfully transmitted (measured in Mbps/Gbps).
Example: A 100 Mbps broadband connection means you can download 100 megabits per second.
Protocol Layers & Service Models
To manage complexity, networks use a layered architecture.
OSI Model (7 Layers) vs. TCP/IP Model (4 Layers)
| OSI Model | TCP/IP Model | Function |
| Physical | Network Interface | Physical connections (Wi-Fi, Ethernet) |
| Data Link | Error detection, MAC addresses | |
| Network | Internet | Routing (IP addresses) |
| Transport | Transport | Reliable data transfer (TCP, UDP) |
| Session | Establishing and managing connections | |
| Presentation | Encryption, data format conversion | |
| Application | Application | User services (HTTP, FTP, DNS, SMTP) |
Common Protocols
- HTTP/HTTPS – Web browsing
- DNS – Converts domain names to IP addresses
- SMTP/IMAP/POP3 – Email protocols
- TCP/UDP – Data transport
Networks Under Attack: Security
Common Cybersecurity Threats
- DoS/DDoS Attacks – Overloading a server to crash it.
- MITM (Man-in-the-Middle) – Intercepting communications.
- Phishing & Malware – Fraudulent emails, malicious software.
Security Measures
- Encryption (AES, SSL/TLS, VPNs) – Protects data.
- Firewalls & Intrusion Detection Systems (IDS) – Blocks unauthorized access.
- Multi-Factor Authentication (MFA) – Adds security layers.
Example: HTTPS encrypts data, preventing MITM attacks.
History of Computer Networks
1960s:
- ARPANET (the first network) is developed by the US Department of Defense.
1970s:
- TCP/IP protocol is introduced.
- Ethernet is invented, enabling local networks.
1980s:
- The Domain Name System (DNS) is introduced.
- Personal computers gain popularity.
1990s:
- The World Wide Web (WWW) is invented by Tim Berners-Lee.
- ISPs grow, making the Internet publicly accessible.
2000s – Present:
- Cloud computing, 5G, AI-driven networks emerge.
