What are Physical Layers Based On?
Physical layers can be based on several different factors, depending on the context. Let's explore the most common interpretations:
Earth's physical layers are categorized based on two primary properties:
1. Chemical Composition:
- The Earth is divided into the core, mantle, and crust based on their chemical makeup. This is a compositional layering. (Source: Phys.org, 30-Apr-2023)
2. Physical Properties:
- Alternatively, layers are defined by their physical characteristics such as density and rigidity. These layers include the lithosphere, asthenosphere, mesosphere (lower mantle), outer core, and inner core. (Sources: Phys.org, 30-Apr-2023; LibreTexts, Feb 14, 2021) The lithosphere, for instance, is rigid, while the asthenosphere is more fluid-like.
Physical Layers in Networking and Communications
In the field of networking and communications, a physical layer refers to the lowest layer of the OSI model. Its basis is the physical medium used for data transmission:
- Transmission Medium: This layer is defined by the physical characteristics of the transmission medium, such as copper wires, fiber optic cables, or wireless signals. Examples of physical layer technologies utilizing these mediums include Ethernet, SONET/SDH, and Wi-Fi. Various techniques exist to identify and authenticate devices based on physical layer characteristics, leveraging features like angle of arrival (AoA) in MIMO systems (Source: arXiv, Jul 11, 2024) or characteristics extracted from preamble signals in Wi-Fi (Source: ScienceDirect, Apr 15, 2023). Machine learning techniques are employed to enhance authentication, sometimes even eliminating thresholds (Source: IEEE Xplore, Jun 27, 2019). Physical layer security, especially in LoRaWAN, requires considerations of vulnerabilities and countermeasures (Source: MDPI, 2022).
Physical Layers in Data Modeling
In database management systems, like Tableau, the physical layer defines how data is physically stored and accessed. (Source: Tableau Help)
