The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes the functions of a communication system or network into seven distinct layers. Each layer has specific responsibilities and interacts with the layers above and below it. The OSI model was developed by the International Organization for Standardization (ISO) to facilitate interoperability and standardization of networking protocols and technologies. Here are the seven layers of the OSI model, listed from the lowest to the highest:

1. Physical Layer (Layer 1):
   • Responsible for physically transmitting raw bits over a physical medium, such as cables, fibers, or wireless connections.
   • It deals with electrical and mechanical aspects of the transmission, such as voltage levels, signaling rates, and modulation.
2. Data Link Layer (Layer 2):
   • Focuses on framing data into frames and providing error detection and correction mechanisms to ensure reliable point-to-point communication.
   • Manages access to the physical medium and controls how devices on the same network segment share access.
3. Network Layer (Layer 3):
   • Handles the routing of data packets between different networks, facilitating end-to-end communication across multiple intermediate devices (routers).
   • Performs logical addressing and subnetting and determines the optimal path for data transmission.
4. Transport Layer (Layer 4):
   • Manages end-to-end communication between devices on different hosts, ensuring data integrity, flow control, and error recovery.
   • Provides segmentation, reassembly, and port-based communication.
5. Session Layer (Layer 5):
   • Manages the establishment, maintenance, and termination of communication sessions between devices.
   • Controls the dialog between devices, synchronization, and session recovery.
6. Presentation Layer (Layer 6):
   • Handles data formatting, encryption, compression, and translation, ensuring that data exchanged between applications is in a format both parties can understand.
   • Manages data representation, character encoding, and protocol conversion.
7. Application Layer (Layer 7):
   • Provides communication services directly to end-user applications.
   • Contains various protocols and services for activities such as email, web browsing, file transfer, and multimedia streaming.

Each layer of the OSI model performs specific functions while interacting with the layers above and below it. This modular design allows for easier development, maintenance, and replacement of network components, and it promotes interoperability between different vendors’ networking products. It’s important to note that while the OSI model is a theoretical framework, real-world networking protocols and technologies often don’t fit perfectly into each layer and may combine functionalities across layers.