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	2.3		Physical Layer (PHY)
	2.3.1		Scope and functions

The MAC layer is only half of the total operation of 802.11. The physical layer (PHY) standard is the other half. Most PHY definitions contain three functional entities, as shown in Figure

. Different PHYs are defined as part of the IEEE 802.11 standard.

Physical Layer Convergence Procedure (PLCP)
The PHY convergence function adapts the capabilities of the physical medium dependent (PMD) system for the MAC service. PLCP defines a method for mapping the MAC sublayer protocol data units (MPDUs) into a framing format suitable for sending and receiving between two or more STAs using the associated PMD system. The PHY exchanges PHY protocol data units (PPDUs) that contain an MPDU, plus additional header information for the physical layer transmitters and receivers. The PLCP also delivers incoming frames from the wireless medium to the MAC sublayer.

The PHY service is provided to the MAC entity at the STA through a service access point (SAP), called the PHY SAP, as shown in Figure .

Physical Medium-dependent (PMD) System
The PMD system defines the characteristics and methods of transmitting and receiving data through a wireless medium between two or more STAs, each using the same PHY system.

Sets of primitives are also defined, to describe the interface between the PLCP and the PMD sublayer. This interface is called the PMD SAP and it is also shown in Figure .

The PMD sublayer accepts PLCP sublayer service primitives and provides the means by which data is actually transmitted or received from the medium. The data stream, timing information, and associated received signal parameters are delivered to the PLCP sublayer. A similar functionality is provided for data transmission. This is illustrated in Figure .