How are the protocol layers in the OSI model related to each other?

The protocol layers in the OSI model are hierarchically related: each layer provides services to the layer above and uses services from the layer below.

This means that data passes through the layers sequentially, starting from the application (top) layer and ending with the physical (bottom) layer during transmission, and vice versa during reception. Each layer adds or processes its own header information (headers, checksums, etc.), providing specific functions, for example:

• Physical layer — transmission of bits over a channel.
• Data link layer — frame formation, error detection.
• Network layer — routing.
• Transport layer — session management and reliability.

Thus, the layers interact closely, ensuring comprehensive data transfer from the application to the physical channel and back.