OSI Layers

7. Application
6. Presentation
5. Session
4. Transport
3. Network
2. Data Link
1. Physical

the OSI model is an open seven-layer model. each layer performs a different function in the exchange of data between different systems. it's successful because each layer build on the activity of the preceding layer. lower layers are considered subordinate to upper layers. within a system a layer can communicate only with the layer immediately above or immediately below itself. between system a layer may communicate only with the same layer in another system. b its peer (peer-to-peer communication)