TCP/IP model

From Wikipedia
Anon


The TCP/IP model or Internet reference model, sometimes called the DoD model (DoD, Department of Defense) 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, and the structure of the Internet is still closely reflected by the TCP/IP model.

The original TCP/IP reference model consists of 4 layers, but has according to some authors evolved into a 5-layer model, where the lowest layer (the network access layer) is split into a physical layer and a datalink layer. 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 five-layer presentations as teaching aids, 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.

An updated IETF architectural document even contains a section entitled: "Layering Considered Harmful". Emphasizing layering as the key driver of architecture is not a feature of the TCP/IP model, but rather of OSI. Much confusion comes from attempts to force OSI-like layering onto an architecture that minimizes their use.