The Open Systems Interconnection (OSI) Reference Model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven abstract layers. Developed by the International Organization for Standardization (ISO), it is not a protocol itself, but rather a model that helps in understanding and designing network architectures. Each layer serves the layer above it and is served by the layer below it, abstracting away the details of the lower layers. The seven layers are:
7. Application Layer: The layer closest to the end user. It provides network services directly to user applications (e.g., HTTP for web Browse, FTP for file transfer).
6. Presentation Layer: Translates, encrypts, and compresses data, ensuring that data sent from the application layer of one system can be read by the application layer of another.
5. Session Layer: Manages and terminates connections (sessions) between applications.
4. Transport Layer: Provides reliable or unreliable data transfer between end points. TCP (reliable) and UDP (unreliable) are the primary protocols at this layer.
3. Network Layer: Responsible for logical addressing (IP addresses) and routing, determining the best path for data to travel across the network.
2. Data Link Layer: Handles physical addressing (MAC addresses) and error detection for a single link between two directly connected nodes.
1. Physical Layer: Defines the physical and electrical specifications for the devices, including cables, connectors, and signaling.
When controlling a programmable power supply over a LAN, all these layers are involved in transmitting the commands from the control PC to the instrument. The model is a valuable tool for troubleshooting network problems by allowing engineers to isolate issues to a specific layer.