What is the OSI model?

The OSI (Open Systems Interconnection) model is a reference network model that describes how data is transmitted over a network through seven logically separated layers. It serves to standardize the interaction of network devices and protocols.

The seven layers of the OSI model:

1. Physical: transmission of bits over a physical channel (cables, radio waves).
2. Data Link: frame formation, media access control, error detection and correction.
3. Network: routing and transmission of packets between networks (e.g., IP).
4. Transport: ensuring reliable data transfer, flow control, and error management (e.g., TCP).
5. Session: management of communication sessions, establishing, maintaining, and terminating connections.
6. Presentation: data transformation, encoding, encryption, compression.
7. Application: interface for applications, providing network services (HTTP, FTP, etc.).

The OSI model helps understand and design network protocols and interactions, although in reality, the TCP/IP stack, which combines some OSI layers, is more commonly used.