Chapter 1 - 802.11 Overview

• • Data link layer - 2 sub-layers
  • • upper : LLC 802.2 logical link layer
    • lower portion: MAC sub-layer (Media Access Control)
    • • interface between lower PHY layer & LLC
  • MSDU
  • • Network layer sends data to data link layer (LLC), becomes known as MAC Service Data Unit
    • • MSDU is IP packet + LLC data
    • 3 frame types: mgt, control, data
    • • only data frames carry payload
      • max MSDU size 2,304 bytes (+ encryption overhead)
  • MPDU
  • • MAC Protocol Data Unit
    • 802.11 frame
    • MAC header + MSDU + 32 bit CRC (FCS)
    • MPDU passed to physical layer for transmission
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  • Physical layer - 2 sub-layers
  • • upper portion: Physical layer convergence procedure (PLCP)
    • • takes MPDU & prepares for transmission (PPDU)
    • lower portion: Physical Media Dependant (PMD)
    • • modulates PPDU and transmits as bits
  • PSDU:
  • • PLCP service data unit
    • Just MPDU in physical layer
  • PPDU:
  • • PLCP sub-layer takes PSDU & adds preamble & PHY header to form PPDU
    •