OSI Layers

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, proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.

* Application layer supports application and end-user processes. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.

* Presentation layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa.

* Session layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end.

* Transport layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.

* Network layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node.

* Data Link layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization.

* Physical layer conveys the bit stream - electrical impulse, light or radio signal through the network at the electrical and mechanical level.