Sunday, October 10, 2010
Open System Interconnection Reference Model
The Open System Interconnection (OSI) reference model describes how information from a software application in one computer moves through a network medium to a software application in another computer. The OSI reference model is a conceptual model composed of seven layers, each specifying particular network functions. The model was developed by the International Organization for Standardization (ISO) in 1984, and it is now considered the primary architectural model for intercomputer communications. The OSI model divides the tasks involved with moving information between networked computers into seven smaller, more manageable task groups. A task or group of tasks is then assigned to each of the seven OSI layers. Each layer is reasonably self-contained so that the tasks assigned to each layer can be implemented independently. This enables the solutions offered by one layer to be updated without adversely affecting the other layers. The following list details the seven layers of the Open System Interconnection (OSI) reference model:
•Layer 7—Application
•Layer 6—Presentation
•Layer 5—Session
•Layer 4—Transport
•Layer 3—Network
•Layer 2—Data link
•Layer 1—Physical
Note A handy way to remember the seven layers is the sentence "All people seem to need data processing." The beginning letter of each word corresponds to a layer.
•All—Application layer
•People—Presentation layer
•Seem—Session layer
•To—Transport layer
•Need—Network layer
•Data—Data link layer
•Processing—Physical layer
Figure 1-2 illustrates the seven-layer OSI reference model.
Figure 1-2 The OSI Reference Model Contains Seven Independent Layers
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