Encapsulation (networking)

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Encapsulation sequence of user data in the TCP/IP protocol stack.

In computer networking, encapsulation is a method of designing modular communication protocols in which logically separate functions in the network are abstracted from their underlying structures by inclusion or information hiding within higher level objects.

For example (see illustration), the Internet is based upon the Internet Protocol Suite (TCP/IP) and most applications use either the User Datagram Protocol (UDP) or Transmission Control Protocol (TCP). In a typical scenario, user data is encapsulated in a UDP datagram to communicate with another application on another host by further encapsulation into IP to enable internetworking to remote sites. IP packets are transmitted within a Link Layer protocol (e.g., Ethernet) to the nearest router.

The physical layer is responsible for physical transmission of the data. Link encapsulation allows local area networking and IP provides global addressing of individual computers; UDP adds application or process selection, i.e., the port specifies the service such as a web or TFTP server.

In discussions of encapsulation, the more abstract layer is often called the upper layer protocol while the more specific layer is called the lower layer protocol. Sometimes, however, the terms upper layer protocols and lower layer protocols are used to describe the layers above and below IP, respectively.

Encapsulation is a characteristic feature of most networking models, including the OSI model, and TCP/IP.

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