The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven abstraction layers. Each layer in the OSI model serves a specific purpose and communicates with the adjacent layers. Here's a brief description of each layer from the bottom (Layer 1) to the top (Layer 7):
- Function: Deals with the physical connection between devices.
- Activities: Transmission and reception of raw bit streams over a physical medium, such as cables or wireless signals.
- Devices: Hubs, cables, repeaters.
- Function: Provides error detection and correction within the physical layer.
- Activities: Frame synchronization, error checking, and flow control.
- Devices: Switches, bridges, network interface cards (NICs).
- Function: Responsible for logical addressing, routing, and forwarding of data packets between different networks.
- Activities: IP addressing, routing, packet forwarding.
- Devices: Routers, Layer 3 switches.
- Function: Manages end-to-end communication, ensuring data integrity and reliability.
- Activities: Segmentation, flow control, error recovery.
- Protocols: TCP (Transmission Control Protocol), UDP (User Datagram Protocol).
- Function: Establishes, manages, and terminates communication sessions between applications.
- Activities: Dialog control, synchronization, session management.
- Example: NetBIOS, RPC (Remote Procedure Call).
- Function: Translates data between the application layer and the lower layers, ensuring that data is in a readable format.
- Activities: Data encryption, compression, and translation.
- Formats: ASCII, JPEG, GIF.
- Function: Provides network services directly to end-users or applications.
- Activities: Network-aware applications, user interfaces.
- Protocols: HTTP, FTP, SMTP.
The OSI model serves as a reference for understanding and designing network architectures, but in practice, the TCP/IP model is more commonly used, which combines the OSI model's top three layers into a single application layer.