# Internet
The Internet is a global system of interconnected computer networks that use the TCP/IP protocol suite to communicate. It originated from ARPANET (1969), a U.S. Department of Defense research project led by [[Vint Cerf]] and [[Bob Kahn]], who developed TCP/IP. The Internet is not a single network but a "network of networks"—millions of private, public, academic, business, and government networks linked by electronic, wireless, and optical technologies. It provides the infrastructure for services including the [[World Wide Web]], email, file transfer (FTP), and streaming.
The Internet's design is fundamentally decentralized—there is no central authority or single point of control. This architecture enabled explosive growth and resilience. Key principles include packet switching (data split into packets routed independently), end-to-end design (intelligence at endpoints, not the network), and open standards maintained by organizations like IETF. The Internet transformed commerce, communication, media, and society, connecting billions of people and devices worldwide. It is often confused with the [[World Wide Web]], which is actually one application layer running on top of Internet infrastructure.
## Internet Architecture
```
┌─────────────────────────────────────────────────────────────┐
│ INTERNET PROTOCOL STACK │
├─────────────────────────────────────────────────────────────┤
│ │
│ APPLICATION LAYER │
│ ┌────────────────────────────────────────────────────┐ │
│ │ HTTP, HTTPS, FTP, SMTP, DNS, SSH, etc. │ │
│ └────────────────────────────────────────────────────┘ │
│ │ │
│ ▼ │
│ TRANSPORT LAYER │
│ ┌────────────────────────────────────────────────────┐ │
│ │ TCP (reliable) │ UDP (fast, unreliable) │ │
│ └────────────────────────────────────────────────────┘ │
│ │ │
│ ▼ │
│ INTERNET LAYER │
│ ┌────────────────────────────────────────────────────┐ │
│ │ IP (Internet Protocol) - addressing & routing │ │
│ └────────────────────────────────────────────────────┘ │
│ │ │
│ ▼ │
│ NETWORK ACCESS LAYER │
│ ┌────────────────────────────────────────────────────┐ │
│ │ Ethernet, Wi-Fi, Fiber, etc. │ │
│ └────────────────────────────────────────────────────┘ │
│ │
└─────────────────────────────────────────────────────────────┘
```
## Key Concepts
| Concept | Description |
|---------|-------------|
| **TCP/IP** | Protocol suite for Internet communication |
| **Packet switching** | Data split into packets, routed independently |
| **IP address** | Unique numerical identifier for devices |
| **DNS** | Translates domain names to IP addresses |
| **Router** | Forwards packets between networks |
| **ISP** | Internet Service Provider—connects users |
## Timeline
| Year | Event |
|------|-------|
| 1969 | ARPANET launched (4 nodes) |
| 1971 | First email sent (Ray Tomlinson) |
| 1973 | TCP/IP development begins (Cerf, Kahn) |
| 1983 | ARPANET adopts TCP/IP ("flag day") |
| 1985 | DNS introduced |
| 1989 | [[World Wide Web]] proposed |
| 1991 | Internet opened to commercial use |
| 1993 | Mosaic browser; Web goes mainstream |
| 1995 | NSFNET decommissioned; full commercialization |
| 1998 | Google founded; ICANN created |
| 2000s | Broadband, mobile Internet |
| 2010s | Internet of Things, cloud computing |
## Internet vs World Wide Web
| Aspect | Internet | World Wide Web |
|--------|----------|----------------|
| **What** | Global network infrastructure | Information system on Internet |
| **Protocol** | TCP/IP | HTTP/HTTPS |
| **Invented** | 1969 (ARPANET) | 1989 (Berners-Lee) |
| **Analogy** | Roads and highways | Cars and trucks on roads |
| **Services** | Email, FTP, Web, VoIP, etc. | Websites, web apps |
## Core Protocols
| Protocol | Layer | Purpose |
|----------|-------|---------|
| **IP** | Internet | Addressing and routing |
| **TCP** | Transport | Reliable, ordered delivery |
| **UDP** | Transport | Fast, connectionless |
| **HTTP/HTTPS** | Application | Web content transfer |
| **DNS** | Application | Name resolution |
| **SMTP/IMAP** | Application | Email |
| **FTP** | Application | File transfer |
## Design Principles
| Principle | Description |
|-----------|-------------|
| **Decentralization** | No central control point |
| **End-to-end** | Intelligence at edges, dumb network |
| **Packet switching** | Efficient, resilient data transfer |
| **Open standards** | Anyone can implement protocols |
| **Layered architecture** | Each layer independent |
| **Best effort** | No guaranteed delivery (TCP adds reliability) |
## Key Figures
| Person | Contribution |
|--------|--------------|
| [[Vint Cerf]] | Co-invented TCP/IP, "Father of Internet" |
| [[Bob Kahn]] | Co-invented TCP/IP |
| [[Tim Berners-Lee]] | Invented World Wide Web |
| J.C.R. Licklider | Visionary, "Intergalactic Network" |
| Leonard Kleinrock | Packet switching theory |
| Ray Tomlinson | Invented email |
| Paul Baran | Distributed networks concept |
## Governance
| Organization | Role |
|--------------|------|
| **IETF** | Protocol standards (RFCs) |
| **ICANN** | Domain names, IP addresses |
| **W3C** | Web standards |
| **Internet Society** | Policy, education |
| **Regional Internet Registries** | IP address allocation |
## Internet Services
| Service | Protocol | Purpose |
|---------|----------|---------|
| **World Wide Web** | HTTP/HTTPS | Hypertext documents |
| **Email** | SMTP, IMAP, POP3 | Electronic mail |
| **File Transfer** | FTP, SFTP | File sharing |
| **Streaming** | RTSP, HLS | Video/audio |
| **VoIP** | SIP, RTP | Voice calls |
| **Messaging** | Various | Real-time chat |
## Statistics (approximate)
| Metric | Value |
|--------|-------|
| **Users** | 5+ billion (60%+ of world population) |
| **Websites** | 1.9+ billion |
| **Connected devices** | 15+ billion (IoT) |
| **Daily emails** | 300+ billion |
| **Data per day** | 400+ exabytes |
## References
- Cerf, V. & Kahn, R. (1974). "A Protocol for Packet Network Intercommunication"
- https://www.internetsociety.org/internet/history-internet/
- https://en.wikipedia.org/wiki/Internet
## Related
- [[World Wide Web]]
- [[TCP IP]]
- [[Hypertext Transfer Protocol (HTTP)]]
- [[Vint Cerf]]
- [[Tim Berners-Lee]]
- [[Uniform Resource Locator (URL)]]