Networking - The TCP/IP Five-Layer Model

The OSI seven-layer model is a useful way to think about how network protocols cooperate, but most real-world networks are built using the protocol suite commonly called TCP/IP. The TCP/IP model is usually described in terms of five layers:

Application (Layer 5)
Transport (Layer 4)
Network (Layer 3)
Data Link (Layer 2)
Physical (Layer 1)

Just as with the OSI model, each TCP/IP layer has its own responsibilities and communicates with the corresponding layers on other systems. The names and number of layers are different, but the underlying ideas are very similar.

In broad terms:

The Physical and Data Link layers describe how bits and frames move across a single link,
The Network layer describes how packets move from one network to another,
The Transport layer describes how complete conversations move between processes on different hosts, and
The Application layer describes the services that users and programs actually see.

The remainder of this section introduces each of the TCP/IP layers and relates them to the OSI model. We will start at the bottom with layer 1, the Physical Layer.

Nah, I want to skip ahead:

Introduction
Physical (Layer 1)
Data Link (Layer 2)
Network (Layer 3)
Transport (Layer 4)
Application (Layer 5)
Conclusion