OSI includes seven layers — each of them is built on the underlying layer. OSI ensures the compatibility of various systems, because the model contributes to the development and implementation of network protocols and technologies in a standard way.
The model implies that the network devices are arranged in layers that differ in their functionality.
L1. Physical Layer
It defines the physical interface between devices on the network, including all the characteristics of the transmission medium. It also sets the rules for transmitting raw data across the medium.
L2. Datalink Layer
L2’s area of responsibility is stable transmission over a physical channel, including error identification and correction, flow control and frame synchronization.
L3. Network Layer
Logical addressing and routing of data packets between network nodes are the tasks of network-layer devices. This includes determining the best path for data transfer, fragmentation and reassembly of packets as needed.
L4. Transport Layer
It provides end-to-end communication of applications on a variety of devices, including reliable data transfer, error recovery and flow control. L4 devices eliminate loss or duplication, and are also responsible for the correct sequence of data transmission.
L5. Session Layer
L5 is responsible for monitoring and managing the communication session between two devices, including creating, managing and terminating sessions. It also provides synchronization and restoration of information exchange in case of interruption.
L6. Presentation Layer
It performs data translation and formatting services, including conversion, encoding, decryption, compression and decompression. L6 ensures that data can be presented in a compatible format between different systems.
L7. Application Layer
L7 interacts directly with the user and their application software. Application layer devices provide network services to the end user, such as email, web browsing, file transfer, and remote access.