|  | 1.1 | The OSI Model
| 1.1.2 | The OSI model layer functions
Each layer of the seven-layer OSI reference model serves a specific function. The functions are defined by the OSI and can be used by any network products vendor. - The layers are: Application -- The application layer provides network services to user applications. For example, a word processing application is serviced by file transfer services at this layer. Presentation -- This layer provides data representation and code formatting. It ensures that the data that arrives from the network can be used by the application, and it ensures that the information sent by the application can be transmitted on the network. Session -- This layer establishes, maintains, and manages sessions between applications. Transport -- This layer segments and reassembles data into a data stream. TCP is one of the transport layer protocols used with IP. Network -- This layer determines the best way to move data from one place to another. Routers operate at this layer. You will find the IP (Internet Protocol) addressing scheme at this layer. Data Link -- This layer prepares a datagram (or packet) for physical transmission across the medium. It handles error notification, network topology, and flow control. This layer uses Media Access Control (MAC) addresses. Physical -- This layer provides the electrical, mechanical, procedural, and functional means for activating and maintaining the physical link between systems. This layer uses physical media such as twisted-pair, coaxial, and fiber-optic cable.