TCP/IP Protocol Suite (Internet Model)
Overview
The TCP/IP Model (originally developed by DARPA/DoD) is the practical protocol architecture that powers the modern Internet. Unlike the 7-layer theoretical Open Systems Interconnection (OSI) Model, the TCP/IP model condenses networking functionality into 4 functional layers.
The 4 Layers & OSI Mapping
| TCP/IP Layer | Corresponding OSI Layers | Key Protocols & Technologies |
|---|---|---|
| Application Layer | Application (L7), Presentation (L6), Session (L5) | HTTP, HTTPS, DNS, SSH, SMTP, TLS, RPC |
| Transport Layer | Transport (L4) | TCP, UDP, QUIC, SCTP |
| Internet Layer | Network (L3) | IPv4, IPv6, ICMP, IPsec, BGP, OSPF |
| Network Access Layer (Link) | Data Link (L2), Physical (L1) | Ethernet (802.3), Wi-Fi (802.11), MAC, ARP, Fiber/Cables |
Core Principles
- End-to-End Principle: Network core (routers) remains simple, doing only packet forwarding; intelligence and state are kept at the endpoints (hosts).
- Robustness Principle (Postel’s Law): “Be conservative in what you send, be liberal in what you accept.”
- Layer Independence: Application layer protocols operate identically whether running over Ethernet, Wi-Fi, or satellite.