The physical layer is divided into two key sublayers: the Physical Layer Convergence Procedure (PLCP) sublayer and the Physical Medium Dependent (PMD) sublayer.
These sublayers work together to ensure reliable data transmission over a physical medium. Let's break down each sublayer:
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Physical Layer Convergence Procedure (PLCP) Sublayer: This sublayer is responsible for adapting the higher layers' data into a format suitable for transmission over the physical medium. It handles functions like:
- Framing: Encapsulating data into frames for transmission.
- Synchronization: Ensuring that the receiver can properly synchronize with the incoming signal.
- Error Detection: Implementing error detection codes to identify corrupted data.
- Clear Channel Assessment (CCA): Determines if the medium is clear before initiating transmission.
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Physical Medium Dependent (PMD) Sublayer: This sublayer is responsible for the actual transmission and reception of data over the physical medium. It handles functions like:
- Signal Encoding/Decoding: Converting digital data into analog signals and vice versa.
- Modulation/Demodulation: Modulating the signal onto the carrier frequency and demodulating it at the receiving end.
- Transmission Power Control: Adjusting the transmission power to optimize signal strength and minimize interference.
- Medium Access: Defining how devices share the physical medium (e.g., CSMA/CD in Ethernet).
- Physical Medium Interface: Specifies the physical characteristics of the connection (e.g., connector type, cable type).
In essence, the PLCP prepares the data for transmission, and the PMD handles the actual physical transmission and reception. The PLCP sublayer acts as an interface between the upper layers of the networking model and the specific physical medium used for transmission managed by the PMD sublayer.
