Open System Interconnection Reference Model

TheOpen 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, eac hi 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 involve d wrth 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 withou t 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—

Sess i on

Layer 4—

Transport

Layer 3—

Network

Layer 2—

Data link

Layer 1—

A hi andy way to remember the seven layers is the sentience "All pe ople seem to need delta processing." The beginning letter of each word cor responds t o a layer.

• People— Presen tation la yer r Se em— Ses sion layer

• Processing— Physical layer

Figure 1-2 illustrates the seven-layer OSI reference model.

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