OSI Reference Model
The Open System Interconnection (OSI) Reference Model defines a networking framework for implementing protocols in seven layers. From top to bottom these layers include the Application, Presentation, Session, Transport, Network, Data-Link, and Physical Layers (the 7 layers of the OSI Model, 2008) as described in this paper.
Open Systems Interconnection -- Reference Model (OSI -- RM) explains the seven layers. At the very top of the OSI model is Layer 7, the Application Layer that interfaces directly to and performs common application services for application processes. These common services provide semantic conversion between associated application processes. Layer 6, the Presentation Layer, resolves syntactical differences in data representation within end-user systems. The Session Layer or Layer 5 manages the dialogue between end-user application processes. Layer 4, the Transport Layer, provides transparent transfer of data between end users. Layer 3, the Network Layer, provides the means of transferring variable length data sequences from a source to a destination via one or more networks. This layer performs network routing, flow control, segmentation / desegmentation, and error control functions. The Data Link Layer, Layer 2, provides the means to transfer data between network entities and to detect and possibly correct errors that may occur in the layer beneath it, the Physical Layer. This bottom layer is responsible for: establishment and termination of a connection to a communications medium; participation in the process where communication resources are effectively shared among multiple users and; conversion between the representation of digital data in user equipment and the corresponding signals transmitted over a communications channel.
Individual layers are not exposed to how the layers above and below them function; they only know how to pass data to them (the seven-layer Open Systems Interconnection Reference Model). Isolating network communications functions in this way minimizes the impact of changes on the entire protocol suite (the seven-layer Open Systems Interconnection Reference Model).
Bibliography
Open Systems Interconnection -- Reference Model (OSI -- RM). http://www.its.bldrdoc.gov/fs-1037/dir-025/_3680.htm
The 7 layers of the OSI Model (2008, March 3). Webopedia. http://www.webopedia.com/quick_ref/OSI_Layers.asp
The seven-layer Open Systems Interconnection Reference Model. http://www.citap.com/documents/tcp-ip/tcpip006.htm
