While the OSI model is a theoretical guide, the TCP/IP model is the practical suite of protocols underpinning today’s Internet. Originally developed in the 1970s by the U.S. Department of Defense, its design emphasizes resilience / networks stay up even when parts fail or are attacked.

TCP/IP Layers (Top ↓ Bottom)

Application Layer

• Encompasses OSI’s Session, Presentation & Application layers (5–7)
• Provides network services directly to applications
• Common protocols: HTTP, HTTPS, FTP, SMTP, IMAP, DNS, Telnet, SSH

Transport Layer

• Maps to OSI’s Transport (Layer 4)
• Ensures end‑to‑end data delivery, flow control & error checking
• Common protocols: TCP (reliable, connection‑oriented), UDP (unreliable, connectionless)

Internet Layer

• Corresponds to OSI’s Network (Layer 3)
• Handles logical addressing, routing & fragmentation
• Common protocols: IP (IPv4/IPv6), ICMP, IPSec, ARP (address resolution)

Link Layer

• Combines OSI’s Data Link & Physical (Layers 1–2)
• Manages framing, MAC addressing, and raw bit transmission on the local network segment
• Common technologies: Ethernet (802.3), Wi‑Fi (802.11), PPP, Frame Relay