The 7 Layers of the Osi Model

The 7 Layers of the OSI Model
Last updated: March 03, 2008

The OSI, or Open System Interconnection, model defines a networking framework for implementing protocols in seven layers. Control is passed from one layer to the next, starting at the application layer in one station and proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.
|Application |This layer supports application and end-user processes. Communication partners are identified, |
|(Layer 7) |quality of service is identified, user authentication and privacy are considered, and any |
| |constraints on data syntax are identified. Everything at this layer is application-specific. This|
| |layer provides application services for file transfers, e-mail, and other network software |
| |services. Telnet and FTP are applications that exist entirely in the application level. Tiered |
| |application architectures are part of this layer. |
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|Presentation |This layer provides independence from differences in data representation (e.g., encryption) by |
|(Layer 6) |translating from application to network format, and vice versa. The presentation layer works to |
| |transform data into the form that the application layer can accept. This layer formats and |
| |encrypts data to be sent across a network, providing freedom from compatibility problems. It is |
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