Physical Layer - covers the physical interface between devices and the rules by which bits are passed from one to another.

Data Link Layer - attempts o make the physical link reliable and provides the means to activate, maintain, and deactivate the link.

Network Layer - provides for the transfer of information between end systems across

some sort communications network.

Transport Layer - provides a mechanism for the exchange of data between end system.

Session Layer - provides the mechanism for controlling the dialogue between applications in end systems.

Presentation Layer - defines the format of the data to be exchanged between applications and offers application programs a set of data transformation services.

Application Layer - provides a means for application programs to access the OSI environment.