Physical layers can be classified based on various factors, depending on the context. Here are some common classifications:
- By physical properties: This classification categorizes layers based on their physical characteristics, such as density, composition, and state of matter. For example, the Earth can be divided into the lithosphere, asthenosphere, mesospheric mantle, outer core, and inner core based on their mechanical properties.
- By functionality: This classification groups layers according to their specific functions or roles in a system. For instance, in a cyber-physical power system, the physical layer encompasses the power grid and protection devices, while the cyber layer comprises communication and control systems.
- By security characteristics: This classification focuses on how different layers contribute to security in a system. In wireless communication, physical layer security techniques can be categorized into secrecy channel codes-based schemes, security techniques based on physical layer properties, and methods involving cooperative communication.
- By events that violate safety: This classification identifies different types of events that threaten the safety of a physical layer. Examples include manipulation or temporary disconnection of physical components, which can be detected and classified using machine learning techniques.
These are just some of the ways physical layers can be classified. The specific classification used depends on the context and the purpose of the analysis.
