The TCP/IP reference model

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In contrast with OSI, the TCP/IP community did not spend a lot of effort defining a detailed reference model; in fact, the goals of the Internet architecture were only documented after TCP/IP had been deployed [Clark88]. 1122, which defines the requirements for Internet hosts, mentions four different layers. Starting from the top, these are :

• an Application layer
• a Transport layer
• an Internet layer which is equivalent to the network layer of our reference model
• a Link layer which combines the functionalities of the physical and datalink layers of our five-layer reference model

Besides this difference in the lower layers, the TCP/IP reference model is very close to the five layers that we use throughout this document.