Introduction to Internet Technologies
An overview of the fundamental concepts, protocols, and services that make the modern Internet work.
1. What Is the Internet?
| Aspect |
Description |
| Definition |
A global network of interconnected computers and devices that communicate using standardized protocols. |
| Scope |
Over 5 billion devices, spanning personal gadgets, servers, IoT sensors, and industrial systems. |
| Core Idea |
“Any‑to‑any” communication: any device can reach any other device (subject to routing, firewalls, etc.). |
2. Key Building Blocks
| Layer (OSI / TCP‑IP) |
Main Function |
Typical Protocols / Technologies |
| Physical |
Transmission of raw bits over a medium |
Ethernet (copper/fiber), Wi‑Fi (802.11), Cellular (LTE/5G), Satellite |
| Data Link |
Framing, error detection, MAC addressing |
Ethernet (IEEE 802.3), Wi‑Fi (IEEE 802.11), PPP |
| Network |
Routing packets across multiple links |
IP (IPv4, IPv6), ICMP, ARP |
| Transport |
End‑to‑end reliability & flow control |
TCP, UDP, SCTP |
| Application |
User‑level services & data formats |
HTTP/HTTPS, FTP, SMTP, DNS, TLS/SSL, WebSocket, MQTT |
The TCP‑IP model collapses the OSI layers into four practical layers (Link, Internet, Transport, Application).
3. Core Internet Protocols
3.1 Internet Protocol (IP)
- IPv4: 32‑bit address space (≈4.3 billion addresses). Uses dotted‑decimal notation (e.g., 192.0.2.1).
- IPv6: 128‑bit address space (≈3.4×10³⁸ addresses). Uses colon‑hex notation (e.g., 2001:db8::1).
- Functions: Addressing, packet fragmentation/reassembly, routing.
3.2 Transmission Control Protocol (TCP)
- Connection‑oriented, reliable byte‑stream service.
- Features: three‑way handshake, sequence numbers, acknowledgments, retransmission, flow control (window), congestion control (e.g., Reno, CUBIC).
3.3 User Datagram Protocol (UDP)
- Connectionless, best‑effort delivery.
- Low overhead, used for latency‑sensitive traffic (DNS, VoIP, video streaming, gaming).
3.4 Hypertext Transfer Protocol (HTTP/HTTPS)
- HTTP: Application‑layer request/response protocol for web resources.
- HTTPS: HTTP over TLS/SSL, providing encryption, integrity, and authentication.
3.5 Domain Name System (DNS)
- Distributed hierarchical database that maps human‑readable domain names to IP addresses.
- Key record types: A, AAAA, CNAME, MX, TXT, SRV.
3.6 Simple Mail Transfer Protocol (SMTP) & POP/IMAP
- SMTP: Pushes email from client to server and between mail servers.
- POP3 / IMAP: Pull email from server to client; IMAP supports server‑side folder management.
3.7 Secure Transport (TLS/SSL)
- Provides encryption, authentication, and data integrity for any TCP‑based application.
- Handshake establishes symmetric keys; certificates bind public keys to domain names.