Encapsulation (networking)

Encapsulation is the <a href="/facts/Computer_network/3w5RM99p">computer-networking</a> process of concatenating layer-specific <a href="/facts/Header_(computing)/DSbn3tM1">headers</a> or <a href="/facts/Trailer_(computing)/majbN4Ha">trailers</a> with a <a href="/facts/Service_data_unit/wJAHNtHm">service data unit</a> (i.e. a <a href="/facts/Payload_(computing)/zN2Pgfq6">payload</a>) for transmitting <a href="/facts/Information/3LdrzXtJ">information</a> over computer networks. Deencapsulation (or de-encapsulation) is the reverse computer-networking process for receiving information; it removes from the <a href="/facts/Protocol_data_unit/UJMVQEt9">protocol data unit</a> (PDU) a previously concatenated header or trailer that an underlying communications layer transmitted. 
Encapsulation and deencapsulation allow the design of modular <a href="/facts/Communication_protocols/5uady7cB">communication protocols</a> so to logically separate the function of each communications layer, and <a href="/facts/Abstraction_(computer_science)/hAnxmJle">abstract</a> the structure of the communicated information over the other communications layers. These two processes are common features of the computer-networking models and protocol suites, like in the <a href="/facts/OSI_model/oxN9Xhjz">OSI model</a> and <a href="/facts/Internet_protocol_suite/KNkxtSpw">internet protocol suite</a>. However, encapsulation/deencapsulation processes can also serve as malicious features like in the <a href="/facts/Tunneling_protocol/jKaT1Czc">tunneling protocols</a>.
The <a href="/facts/Physical_layer/WuATCrVw">physical layer</a> is responsible for physical transmission of the data, link encapsulation allows <a href="/facts/Local_area_network/edUDxJ6J">local area networking</a>, <a href="/facts/Internet_Protocol/Qq6VeEal">IP</a> provides global addressing of individual computers, and <a href="/facts/Transmission_Control_Protocol/WW4sPrt9">TCP</a> selects the process or application (i.e., the <a href="/facts/TCP_and_UDP_port/ygoHVKNC">TCP or UDP port</a>) that specifies the service such as a <a href="/facts/Web_server/A4GS6thA">Web</a> or <a href="/facts/Trivial_File_Transfer_Protocol/TslBlcvJ">TFTP</a> server.
For example, in the <a href="/facts/Internet_protocol_suite/KNkxtSpw">IP suite</a>, the contents of a web page are encapsulated with an <a href="/facts/HTTP_header/hEkcQe2f">HTTP header</a>, 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 <a href="/facts/Data_stream/57yDhBCd">stream</a> of <a href="/facts/Bit/S972NSaD">bits</a>, where it is decapsulated 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.

Encapsulation (networking) open-in-new

Encapsulation (networking)