→ It is a reference model that describes how information frm a software application in one computer moves through a physical medium to the software application in another computer.

→ It was developed by the ISO in 1984.

→ ISO stands for International Organization for standardization.

→ It breaks down the process of network communication into seven layers.

→ Each leyer provides a different service and interacts with the layers directly and below it.

→ This layered approach helps ensure interoperability between different systems.

→ This modular approach simplifies the design and troubleshooting of complex network systems.

1. Physical Layer

Transmits raw binary data (1s and 0s) over a physical medium.
Defines hardware components like cables, switches, and transmission techniques.
Handles bit rate, electrical signals, and connection types.

2. Data Link Layer

Manages node-to-node data transfer and error detection/correction.
Defines data framing, flow control, and physical addressing (e.g., MAC addresses).
Devices: Switches, bridges.

3. Network Layer

Responsible for routing data across different networks.
Utilizes logical addressing (e.g., IP addresses) for path selection.
Devices: Routers.

4. Transport Layer

Ensures reliable data transfer through error detection and flow control.
Handles data segmentation and reassembly.
Protocols: TCP (reliable), UDP (faster but less reliable).

5. Session Layer

Manages sessions or connections between applications.
Establishes, maintains, and terminates communication sessions.
Provides session checkpointing and recovery.

6. Presentation Layer

Translates, encrypts, and compresses data for the application layer.
Ensures data is in a readable format for the receiving application.
Examples: Data encryption, format conversion.

7. Application Layer

Closest layer to the end-user, enabling access to network services.
Supports application protocols like HTTP, FTP, and SMTP.
Manages file transfers, email, and web browsing interfaces.

Few applications of OSI model are:

*Web browsing.

*Email.

*File transfer.

*Video Streaming.

*Voice and Video calls.

*Local Area Networks.

OSI Model [Open System Interconnection]