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 serves a specific purpose and interacts with the layers adjacent to it. The model was developed by the International Organization for Standardization (ISO) to facilitate communication between different systems and devices. The OSI model does not directly specify the technologies or protocols to be used in each layer but provides a clear and systematic way to understand and discuss network functions.
The seven layers of the OSI model, from the lowest to the highest, are as follows:
Physical Layer (Layer 1):
Focus: Physical medium, transmission of raw binary data over a physical channel.
Examples: Cables, connectors, voltage levels.
Data Link Layer (Layer 2):
Focus: Framing, addressing, error detection, and flow control at the data link level.
Examples: Ethernet, Wi-Fi, PPP.
Network Layer (Layer 3):
Focus: Logical addressing, routing, and forwarding of data packets between devices on different networks.
Examples: IP (Internet Protocol), ICMP (Internet Control Message Protocol).
Transport Layer (Layer 4):
Focus: End-to-end communication, segmentation, flow control, error recovery.
Examples: TCP (Transmission Control Protocol), UDP (User Datagram Protocol).
Session Layer (Layer 5):
Focus: Establishment, maintenance, and termination of sessions or connections between applications.
Examples: NetBIOS, RPC (Remote Procedure Call).
Presentation Layer (Layer 6):
Focus: Translation, encryption, and compression of data formats between applications.
Examples: SSL/TLS, JPEG, GIF.
Application Layer (Layer 7):
Focus: Interaction with end-user applications, network services, and user interfaces.
Examples: HTTP, FTP, SMTP.
The OSI model provides a conceptual framework that helps in understanding the interactions and functions of various network protocols. However, in practice, the Internet Protocol Suite (TCP/IP) has become the dominant networking architecture, and its structure aligns closely with the OSI model but with fewer layers.