Describe the layers of OSI reference model.

OSI Model: Open system interconnection a model of communication between co-operating devices. It defines seven layer architecture of communication.

Figure: The OSI layers

Application layer: Application layer provides access to the OSI environment for users and also provides distributed information services.

Presentation layer: Presentation layer provides independence to the application processes from differences in data representation.

Session layer: Session layer provides the control structure for communication between applications, establishes, manages and terminates connections between co-operating applications.

Transport layer: Transport layer provides reliable, transparent transfer of data between end points provides end-to-end error recovery and flow control.

Network layer: Provides upper layers with independence from the data transmission and switching technologies used to connect systems, responsible for establishing, maintaining and terminating connections.

Data link layer: Data link layer provides for the reliable transfer of information across the physical link sends blocks of data with the necessary synchronization, error control and flow control.

Physical layer: Concerned with transmission of unstructured bit stream over physical medium; deals with the mechanical, electrical, functional and procedural characteristics to across the physical medium.