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TCP/IP is a set of protocols that evolved from the US Defense Advanced Research Projects Agency (DARPA) in the 1970s and was intended for use among researchers who wished to share computers across multiple universities. TCP/IP was the predecessor to the Internet and is still the predominant set of protocols used in the Internet today. The success of TCP/IP is largely attributed to the creation of the TCP/IP standards based on practical experience and on looser TCP/IP standards. The TCP/IP standards were developed through the Internet Engineering Task Force (IETF), and are less rigid than those outlined in the OSI model. TCP/IP standards are described in depth in Request for Comment (RFC) documents.

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<tcp-ip example model>Below is a figure depicting how the TCP/IP protocol suite fits into the OSI model:

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The follow figure demonstrates the use of TCP/IP from application-to-application across a network:

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Note how the web browser and TCP on the end hosts traverse the entire network, while IP and Ethernet are utilized twice – once on each side of the router. The TCP/IP protocol suite is often referred to as a "stack", where each layer is pushed or popped as necessary in order to traverse each network.

Data Link Layer

• access to physical medium
• error recovery and flow control between hosts on the same subnet
• various protocols e.g. Ethernet

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Internetwork Layer

• routing and forwarding of packets
• various protocols e.g. IPv4, IPv6, BGP, RIP

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These standards can be subdivided into Logical Link Control (LLC) and Media Access Control (MAC). The figure below shows how these categorizations fit into the OSI model:

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Media Access Control (MAC)

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The MAC sublayer controls access to a medium that is shared by several entities. It is designed to balance fairness and efficiency and includes link layer addressing and error detection (in the form of a checksum).

Logical Link Control (LLC)

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The LLC sublayer is a point-to-point link layer protocol that resides above the MAC sublayer and the shared medium. LLC abstracts away from higher layers the contention that can be present when using a shared medium. It provides three types of service to higher layers:

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Each network protocol has both control information and data. The control information is typically implemented as a header with the data following this header. The data is often referred to as the payload of the header.

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Note that some protocols also use a trailer at the payload of the header.<figure for header + payload>end of the payload, such as Ethernet, which includes a trailing checksum.

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When a network protocol belonging to a higher layer is implemented and placed within the data or payload of a lower layer network protocol, the higher layer protocol is said to be encapsulated within the lower layer. As such, a network protocol, if encapsulated is both a payload and a header + data. It is the payload of the layer below it and it is itself a network protocol with separate header and data.

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