How many levels are in the OSI model? List them.

The OSI model consists of 7 layers:

1. Physical — transmission of bits over physical channels.
2. Data Link — organization of frame transmission, error detection and correction.
3. Network — routing and logical addressing (e.g., IP).
4. Transport — ensuring reliable data transfer, flow control (TCP, UDP).
5. Session — session management, establishing, maintaining, and terminating connections.
6. Presentation — data transformation, encoding, encryption.
7. Application — interface for applications, support for high-level protocols (HTTP, FTP, SMTP).