1. Physical layer - Deals with physical attachment to communications lines.

2. Data link layer -  Provides transfer and control of data over communications lines, error correction, etc.

3. Network layer -  Adds destination switching, routing, and relaying functions and presents them independently of the network in use.

4. Transport layer - Provides user-to-user services, including multiplexing, to make the most effective use of network facilities. It enhances the quality of service.

5. Session layer - Controls the dialogue between users and supports synchronisation of their activity.

6. Presentation layer -  Allows for the selection of the representation of data, resolving differences between systems.

7. Application layer -  Provides the interface to user applications and common services, such as file transfer and terminal support.