OSI vs TCP/IP model

Both are layered reference models for network communication.

   OSI (7 layers)          TCP/IP (4 layers)
  Application  ─┐
  Presentation  ├────────▶  Application
  Session      ─┘
  Transport    ────────▶  Transport
  Network      ────────▶  Internet
  Data Link    ─┐
  Physical     ─┘──────▶  Network Access (Link)

Similarities

1. Both use a layered architecture, where each layer provides services to the layer above and uses the one below.
2. Both have application, transport, and network layers with similar functions.
3. Both use packet switching (not circuit switching).
4. Both rely on encapsulation: each layer adds its own header as data moves down.
5. Both are used to describe networking and to develop compatible, interoperable protocols.
6. Layer functions are independent, so one layer can change without affecting the others.

Differences

Basis	OSI model	TCP/IP model
Full form	Open Systems Interconnection	Transmission Control Protocol / Internet Protocol
Developed by	ISO (1984)	US Department of Defense (ARPANET)
Layers	7	4 (sometimes shown as 5)
Nature	Generic, protocol-independent reference model	Protocol-specific model built around TCP/IP
Approach	Vertical: model first, protocols later	Horizontal: protocols first, model later
Session and presentation	Separate layers	Merged into the application layer
Transport layer	Connection-oriented service only, for reliability	Both TCP (reliable) and UDP (unreliable)
Network layer	Supports both connection-oriented and connectionless	Connectionless (IP) only
Service, interface, protocol	Clearly separated concepts	Not clearly separated
Reliability of design	Well defined, but complex and rarely used in practice	Simple, practical, and the standard of the Internet
Protocols	Fit in after the model was made	Built first, e.g. HTTP, FTP, TCP, UDP, IP
Usage	Mainly for teaching and reference	Actually used in networks