The OSI (Open Systems Interconnected) Model describes the universal standard of communication functions of a telecommunication system or computing system.
| layer | Description | PDU | Function |
|---|---|---|---|
| 7 | Application | Data | High-level APIs, including resource sharing, remote file access |
| 6 | Presentation | Data | Translation of data between a networking service and an application; including character encoding, data compression and encryption/decryption |
| 5 | Session | Data | Managing communication sessions, i.e., continuous exchange of information in the form of multiple back-and-forth transmissions between two nodes |
| 4 | Transport | Segment, Datagram | Reliable transmission of data segments between points on a network, including segmentation, acknowledgement and multiplexing |
| 3 | Network | Packet | Structuring and managing a multi-node network, including addressing, routing and traffic control |
| 2 | Data link | Frame | Reliable transmission of data frames between two nodes connected by a physical layer |
| 1 | Physical | Bit, Symbol | Transmission and reception of raw bit streams over a physical medium |