Which of the following is NOT a layer in the OSI model?

The OSI model, or Open Systems Interconnection model, has seven distinct layers that define how data communications should take place between different computing systems. The layers of the OSI model are:

1. Application layer

2. Presentation layer

3. Session layer

4. Transport layer

5. Network layer

6. Data Link layer

7. Physical layer

Each of these layers serves a specific function in the communication process. The Application layer is where end-user software operates, providing services for applications. The Presentation layer is responsible for data translation and formatting, ensuring that data is presented in a usable format. The Transport layer handles end-to-end communication and data flow control between devices.

The Encryption layer, however, is not among these recognized layers within the OSI model. While encryption can be implemented at various levels of the OSI model (such as within the Application or Presentation layers), it does not constitute a separate layer of its own in the context of the OSI model. This distinction is important for understanding the structure and functions of network communications as per the OSI framework.