TCP/IP Reference Model

The TCP/IP protocol suite was developed prior to the OSI model. The original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application. As shown in the following illustration, each layer of the TCP/IP model corresponds to one or more layers of the seven-layer Open Systems Interconnection (OSI) reference model proposed by the International Standards Organization (ISO).

OSI and TCP/IP layers

Protocols and networks in the TCP/IP model

Application

• Defines, TCP/IP application protocols, and how host programs interface with transport layer services to use the network.

Transport

• Provides communication session management between host omputers.

Internet

• Packages data into IP datagrams, which contain source and destination address information that is used to forward the datagrams between hosts and across networks. Performs routing of IP datagrams.

Host to Network Layer

• Specifies details of how data is physically sent through the network.

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