What is "encapsulation"

Encapsulation \En*cap`su*la"tion\, n. (Physiol.) The act of inclosing in a capsule; the growth of a membrane around (any part) so as to inclose it in a capsule.

1859, "act of surrounding with a capsule," noun of action from encapsulate. Figurative use by 1934.

n. 1 The act of enclosing in a capsule; the growth of a membrane around (any part) so as to enclose it in a capsule. 2 (label en programming object-oriented) Grouping together an object’s ‘state’ (its data) and the operations that may alter or interrogate it (its methods).Huw Collingbourne, ''The Book of Ruby'', ''‘Encapsulation’ or ‘Information Hiding’?'', page 140 3 (label en networking) The process of arrange data into packets that can be transmitted using a given protocol.

1. n. the condition of being enclosed (as in a capsule); "the encapsulation of tendons in membranous sheaths"

2. the process of enclosing (as in a capsule)

Encapsulation may refer to:

In programming languages, encapsulation is used to refer to one of two related but distinct notions, and sometimes to the combination thereof:

• A language mechanism for restricting direct access to some of the object's components.
• A language construct that facilitates the bundling of data with the methods (or other functions) operating on that data.

Some programming language researchers and academics use the first meaning alone or in combination with the second as a distinguishing feature of object-oriented programming, while other programming languages which provide lexical closures view encapsulation as a feature of the language orthogonal to object orientation.

The second definition is motivated by the fact that in many OOP languages hiding of components is not automatic or can be overridden; thus, information hiding is defined as a separate notion by those who prefer the second definition.

The features of encapsulation are supported using classes in most object-oriented programming languages, although other alternatives also exist.

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.

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

During encapsulation, each layer builds a protocol data unit (PDU) by adding a header (and sometimes trailer) containing control information to the PDU from the layer above. For example, in the Internet protocol suite, the contents of a web page are encapsulated with an HTTP header, then by a TCP header, an IP header, and, finally, by a frame header and trailer. The frame is forwarded to the destination node as a stream of bits, where it is decapsulated (or de-encapsulated) into the respective PDUs and interpreted at each layer by the receiving node.

The result of encapsulation is that each lower layer provides a service to the layer or layers above it, while at the same time each layer communicates with its corresponding layer on the receiving node. These are known as adjacent-layer interaction and same-layer interaction, respectively.

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 both the OSI model and TCP/IP suite of protocols.