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2025-08-02Security Fundamentals5 min read

TCP/IP Model

How the TCP/IP Model's four layers map to the OSI Model's seven — and why this practical, DARPA-built framework became the real backbone of the internet while OSI stayed largely theoretical.

TCP/IP was created by the U.S. Department of Defense (DARPA) in the 1970s for the ARPANET project (predecessor of the Internet).

The OSI Model was designed first but it remained theoretical. The TCP/IP Model, on the other hand, was created practically and became the real backbone of the Internet.

The layers of TCP/IP

Unlike the OSI Model, it consists of 4 layers namely:

  1. Application Layer.
  2. Transport layer.
  3. Network layer.
  4. Network Access layer.

If we are familiar with the OSI Model, it is easy to understand these and compare TCP/IP Model with the OSI Model.

OSI Model vs. TCP/IP Model

TCP/IP LayerCorresponding OSI Layer(s)
ApplicationApplication, Presentation, Session
TransportTransport
NetworkNetwork
Network AccessData Link, Physical

Application Layer

The Application Layer is the top layer of the TCP/IP model and closest to the user. Apps like web browsers, email clients or file sharing tools works on this layer. It acts like a bridge between software and the lower layers of the network.

Protocols of the Layer:

  • HTTP
  • FTP
  • DNS
  • SMTP
  • DHCP

Transport layer

The layer is responsible for delivering data reliably, safely, completely and in a right order.

Protocols of the Layer:

TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are the two main protocols here.

TCP is called connection oriented protocol while UDP is known as connection less protocol.

TCP is used when data must be correct and complete. It checks for errors, resends missing pieces and keeps everything in order. On the other hand, UDP (User Datagram Protocol) is faster but doesn't guarantee delivery. It is useful for things like live video or online games where speed matters more than perfect accuracy.

Network layer

Network layer is responsible for data routing. It means finding the best path for data to travel across different networks. It stores the IP addresses and, when data is transmitted from a node on one LAN to a node on a different LAN, the Network Layer is used.

Protocols of the Layer:

  • Internet Protocol (IP) — Responsible for packet addressing and routing.
  • Internet Control Message Protocol (ICMP) — Responsible for error reporting and diagnostics.
  • Address Resolution Protocol (ARP) — Responsible for mapping IP address to MAC address with a LAN.
  • Other protocols: IPsec, RARP and IGMP.

Network Access Layer

The bottom layer of the suit where actual physical connection between devices on the same LAN, such as Ethernet.

When a hosts or routers IP process chooses to send an IP packet to a different router or host, that host or router then uses the Network Access layer details to send that packet to the next host or router.

Protocols and Technologies:

  • Ethernet — most widely used protocol for wired networks which uses MAC addresses to identify devices.
  • MAC — Not a protocol, but control rules that manage who can transmit data on shared channels.
  • Point-to-Point Protocol (PPP) — Used for direct communication between two nodes and supports authentication, encryption and compression.

The TCP/IP framework is the digital nervous system of the internet — a living, breathing system that supports everything from websites and emails to gaming and streaming.

Whether you're defending networks, building applications or just curious about how things work — learning TCP/IP will give you superpowers.