In which situations is it permissible to use the '==' operator when comparing string values?

The OSI model (Open Systems Interconnection) is a conceptual network model that divides the process of network communication into seven layers:

1. Physical layer — transmission of bits over physical media (cables, radio channels).
2. Data Link layer — organization of frame transmission, error detection and correction at the physical layer.
3. Network layer — routing and transmission of packets between different networks.
4. Transport layer — ensuring reliable data transfer, flow control, and error handling.
5. Session layer — establishing, managing, and terminating communication sessions.
6. Presentation layer — data transformation, encoding, encryption.
7. Application layer — interaction with end-user applications (e.g., HTTP, FTP).

It is used for standardizing network protocols and simplifying the development of network solutions, allowing each layer to be developed and tested independently.