TCP/IP Model

The TCP/IP model or Internet reference model, sometimes called the DoD model (DoD stands for the Department of Defense) or the ARPANET reference model, is a layered abstract description for communications and computer network protocol design. It was created in the 1970s by DARPA for use in developing the Internet's protocols. The structure of the Internet is still closely reflected by the TCP/IP model.

The original TCP/IP reference model consists of 4 layers. However, no IETF standards-track document has accepted a five-layer model, probably since physical layer and data link layer protocols are not standardized by IETF. IETF documents deprecate strict layering of all sorts. Given the lack of acceptance of the five-layer model by the body with technical responsibility for the protocol suite, it is not unreasonable to regard the occasional five-layer presentation as a teaching aid, making it possible to talk about non-IETF protocols at the physical layer.

This model was developed before the OSI Reference Model, and the Internet Engineering Task Force (IETF), which is responsible for the model and protocols developed under it, has never felt obligated to be compliant with OSI. While the basic OSI model is widely used in teaching, OSI, as presented as a seven-layer model, does not reflect real-world protocol architecture (RFC 1122) as used in the dominant Internet environment.