Like most networking software, TCP/IP is modelled in layers. This layered representation leads to the term protocol stack, which refers to the stack of layers in the protocol suite. It can be used for positioning (but not for functionally comparing) the TCP/IP protocol suite against others, such as Systems Network Architecture (SNA) and the Open System Interconnection (OSI) model.

Functional comparisons cannot easily be extracted from this, as there are basic differences in the layered models used by the different protocol suites. By dividing the communication software into layers, the protocol stack allows for division of labour, ease of implementation and code testing, and the ability to develop alternative layer implementations.

Layers communicate with those above and below via concise interfaces. In this regard, a layer provides a service for the layer directly above it and makes use of services provided by the layer directly below it. For example, the IP layer provides the ability to transfer data from one host to another without any guarantee to reliable delivery or duplicate suppression. Transport protocols such as TCP make use of this service to provide applications with reliable, in-order, data stream delivery.
Figure 2 shows how the TCP/IP protocols are modelled in four layers.

These layers include:

• Application layer
• Transport layer
• Internetwork layer
• Network interface layer