OSI Model (7 Layers) 

The Open Systems Interconnection (OSI) model is a conceptual framework used to understand network interactions in seven layers. Each layer performs a specific function, and data moves through these layers in both directions when communicated between devices.

        Layer 1: Physical Layer

        • Deals with the physical medium (e.g., cables, switches) used to transmit data.

        • Defines electrical signals, voltage levels, and data rates.

• Examples: Ethernet cables, fiber optics, Wi-Fi.

Layer 2: Data Link Layer

• Responsible for node-to-node data transfer and error detection/correction.

• Defines MAC (Media Access Control) addresses, used for device identification on a network.

• Examples: Ethernet, PPP (Point-to-Point Protocol).

Layer 3: Network Layer

• Responsible for routing data from the source to the destination across multiple networks.

• Manages IP addresses and packet routing.

• Examples: IP (Internet Protocol), routers.

Layer 4: Transport Layer

• Ensures reliable data transfer between devices.

• Manages flow control, error detection, and retransmission of lost data.

• Examples: TCP (Transmission Control Protocol), UDP (User Datagram Protocol).

Layer 5: Session Layer

• Manages sessions or connections between applications, ensuring they remain open and functional.

• Handles session establishment, maintenance, and termination.

• Examples: NetBIOS, RPC (Remote Procedure Call).

Layer 6: Presentation Layer

• Translates data between the application layer and the lower layers.

• Responsible for data encryption, compression, and formatting (e.g., ASCII, JPEG).

• Examples: SSL/TLS, JPEG, GIF.

Layer 7: Application Layer

• Provides network services directly to end-user applications.

• Handles high-level protocols that support user data exchange.

• Examples: HTTP, FTP, DNS, SMTP.