The Open Systems Interconnection protocols are a family of information exchange standards developed jointly by the
ISO
The International Organization for Standardization (ISO ; ; ) is an independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries.
Me ...
and the
ITU-T
The International Telecommunication Union Telecommunication Standardization Sector (ITU-T) is one of the three Sectors (branches) of the International Telecommunication Union (ITU). It is responsible for coordinating Standardization, standards fo ...
. The standardization process began in 1977.
While the seven-layer
OSI model
The Open Systems Interconnection (OSI) model is a reference model developed by the International Organization for Standardization (ISO) that "provides a common basis for the coordination of standards development for the purpose of systems inter ...
is often used as a reference for teaching and documentation, the protocols originally conceived for the model did not gain popularity, and only
X.400,
X.500, and
IS-IS
Intermediate System to Intermediate System (IS-IS, also written ISIS) is a routing protocol designed to move information efficiently within a computer network, a group of physically connected computers or similar devices. It accomplishes thi ...
have achieved lasting impact. The goal of an open-standard protocol suite instead has been met by the
Internet protocol suite
The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suite are ...
, maintained by the
Internet Engineering Task Force
The Internet Engineering Task Force (IETF) is a standards organization for the Internet standard, Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster ...
(IETF).
Overview
The OSI
protocol
Protocol may refer to:
Sociology and politics
* Protocol (politics)
Protocol originally (in Late Middle English, c. 15th century) meant the minutes or logbook taken at a meeting, upon which an agreement was based. The term now commonly refers to ...
stack is structured into seven conceptual layers. The layers form a hierarchy of functionality starting with the physical hardware components to the user interfaces at the software application level. Each layer receives information from the layer above, processes it and passes it down to the next layer. Each layer adds encapsulation information (
header) to the incoming information before it is passed to the lower layer. Headers generally include address of source and destination, error control information, protocol identification and protocol parameters such as flow control options and sequence numbers.
Layer 1: physical layer
This layer deals with the physical plugs, sockets, electrical/optical specifications and the required
line code
In telecommunications, a line code is a pattern of voltage, current, or photons used to represent digital data transmission (telecommunications), transmitted down a communication channel or written to a storage medium. This repertoire of signal ...
s.
The physical layer includes the medium over which the digital signals are transmitted. It can be
twisted pair
Twisted pair cabling is a type of communications cable in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted balanced ...
,
coaxial cable
Coaxial cable, or coax (pronounced ), is a type of electrical cable consisting of an inner Electrical conductor, conductor surrounded by a concentric conducting Electromagnetic shielding, shield, with the two separated by a dielectric (Insulat ...
,
optical fiber
An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at ...
,
wireless
Wireless communication (or just wireless, when the context allows) is the transfer of information (''telecommunication'') between two or more points without the use of an electrical conductor, optical fiber or other continuous guided transm ...
, or other transmission media.
Layer 2: data link layer
The
data link layer
The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer p ...
packages raw bits from the physical layer into
frames
A frame is often a structural system that supports other components of a physical construction and/or steel frame that limits the construction's extent.
Frame and FRAME may also refer to:
Physical objects
In building construction
*Framing (con ...
(logical, structured packets for data). It is specified i
ITU-T Rec. X.212 [ISO/IEC 8886/nowiki>">SO/IEC 8886">ITU-T Rec. X.212
[ISO/IEC 8886
/nowiki>br>ITU-T Rec. X.222
and others. This layer is responsible for transferring frames from one host to another. It might perform error checking. This layer further consists of two sublayers: MAC
Mac or MAC may refer to:
Common meanings
* Mac (computer), a line of personal computers made by Apple Inc.
* Mackintosh, a raincoat made of rubberized cloth
* Mac, a prefix to surnames derived from Gaelic languages
* McIntosh (apple), a Canadi ...
and Logical link control">LLC
A limited liability company (LLC) is the United States-specific form of a private limited company. It is a business structure that can combine the pass-through taxation of a partnership or sole proprietorship with the limited liability of a ...
/nowiki>].