The ISO-OSI (International Organization for Standardization – Open Systems Interconnection) reference model is a conceptual framework that standardizes the functions of a networking system into seven distinct layers. Each layer serves a specific purpose and interacts with the layers directly above and below it.

1. **Physical Layer**: This layer deals with the physical connection between devices, including cables, switches, and the transmission of raw bitstreams over a physical medium.

2. **Data Link Layer**: Responsible for error detection and correction, this layer organizes data into frames and manages the flow of data between devices on the same network segment.

3. **Network Layer**: This layer handles routing and forwarding of data packets across different networks. It defines logical addressing (e.g., IP addresses) to identify devices on a network.

4. **Transport Layer**: Ensuring reliable data transfer, this layer manages end-to-end communication. It provides error recovery and flow control through protocols such as TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).

5. **Session Layer**: This layer establishes, manages, and terminates sessions between applications, allowing them to communicate effectively.

6. **Presentation Layer**: It translates data between the application layer and the network. This includes data encoding, encryption, and compression to ensure proper data representation.

7. **Application Layer**: The topmost layer, it provides network services directly to end-user applications, such as web browsers and email clients.

The ISO-OSI model serves as a universal standard for networking, allowing different systems to communicate seamlessly, thereby promoting interoperability across various technologies.