Provides means for the application process (users) to access the OSI environment.

Provides independence to the application processes for different data representation (syntax).

Provides means to organize and to synchronize the dialogue and to manage the data exchange. Provides means to establish, maintain and terminate a session.

Provides transparent and reliable transfer of data between the higher layers. Provides functions as end-to-end flow control and error correction.

Provides to the higher layers independence from routing and relay consideration associated with the establishment and operation of a given network connection. Provides means to establish, maintain, and terminates network connections.

Provides functional and procedural means for reliable transfer of data over the physical link.

Provides mechanical, electrical, functional and procedural means to activate, maintain, and de-activate physical connections for bit transmission over the physical medium.