What is the TCP/IP model?

The TCP/IP model (also called the Internet model) is a practical 4-layer framework that describes how data is transmitted over the Internet. It is the basis of all modern networking. The layers are: Application Layer (corresponds to OSI layers 5-7 — HTTP, HTTPS, FTP, SMTP, DNS, SSH), Transport Layer (corresponds to OSI layer 4 — TCP and UDP, port numbers), Internet Layer (corresponds to OSI layer 3 — IP, ICMP, routing), and Network Access Layer (corresponds to OSI layers 1-2 — Ethernet, Wi-Fi, MAC addresses). Unlike OSI, TCP/IP is not just a theoretical model — it was built from the protocols that actually power the Internet, developed by DARPA in the 1970s.