OSI is a 7-layer reference model that helps you understand and troubleshoot networking step by step.
TCP/IP is the practical model used on real networks and the internet; it has fewer layers because it groups some OSI layers together.
| Layer | Name | Description |
|---|---|---|
| 7 | Application | The application (i.e. Web browsers, email programs, etc…) |
| 6 | Presentation | Establish data formatting and data translation |
| 5 | Session | Creates the setup, controls the connection and ends the teardown between devices |
| 4 | Transport | The transport layer provides the functional and procedural means of transferring variable-length data sequences from a source host to a destination host from one application to another across a network while maintaining the quality-of-service functions. Transport protocols may be connection-oriented or connectionless. |
| 3 | Network | Transfer packets from one node to another connected in “different networks” |
| 2 | Data Link | Node-to-node data transfer, defines the protocol to establish/terminate a connection between two physically connected devices. Defines protocol for flow control between them |
| 1 | Physical | Transmits raw data between a device and a transmission medium |
| Layer | Name | Description |
|---|---|---|
| 5 | Application | The services and protocols apps use (i.e. web traffic) |
| 4 | Transport | Protocols like TCP and UDP, plus port numbers |
| 3 | Network | IP Addresses & routing between networks |
| 2 | Data Link | MAC Addresses & local network communication |
| 1 | Physical | Cables, signals, network cards, electrical or wireless transmission |
Data link and Physical layers can be merged into the Network Interface layer in the TCP/IP 4 layers model.