PSDUs

PSDU stands for PHY Service Data Unit. In digital communications, a PSDU is the data unit used at the physical layer when transmitting or receiving data. It represents the data that is handed from the data-link layer (MAC) to the physical layer for transmission, and conversely the data recovered by the PHY and handed to the MAC on reception. The exact contents of a PSDU vary by standard, but it generally corresponds to the MAC Protocol Data Unit (MPDU) or a higher-layer SDU encapsulated for the PHY. In many IEEE 802 standards, the PSDU comprises the MPDU (including MAC header, payload and frame check sequence). The physical layer then surrounds the PSDU with its own framing, such as preambles, headers and pilots, and performs modulation and transmission.

During transmission, the MAC layer passes the PSDU to the PHY after any necessary segmentation or buffering. The PHY encodes, modulates and transmits the PSDU over the channel, adding the physical layer overhead. During reception, the PHY decodes the received signal to recover the PSDU, which is then passed to the MAC, where the MPDU is extracted and delivered to higher layers.

In summary, PSDU is a connective data unit at the boundary between MAC and PHY, with content dependent on standard. See also MPDU, PLCP, and the distinction between PHY and MAC data units.