Wednesday, February 7, 2018

Chapter 2 - Data Units, their names and roles

As data is passed through the layers and sublayers, they take on different forms. Each with different information being added or stripped depending on the direction (up or down through the layers.) Each of these forms will have a different name to help differentiate them from each other.

MSDU - MAC Service Data Unit - This is the upper layer data from L7-L3 that needs to be passed along. Technically its actually the LPDU from the LLC that was passed along to the MAC layer thus making it a MSDU.
  • All 802.11 frames that contain data have an MSDU. But Management frames do not contain any data so they don't contain an MSDU.

MPDU - MAC Protocol Data Unit - This is the MSDU that is being handed down to the PLCP (top sublayer in the PHY layer)

PSDU - PLCP Service Data Unit - This is actually the MPDU only now that its on the PHY layer its called the PSDU.
  • The PLCP sublayer adds information to the PSDU and passes it along to the PMD sublayer calling that new data unit containing the PSDU and extra information a PPDU.

PPDU - PLCP Protocol Data Unit - This is the last stop. Everything that has been passed down from L7 and encapsulated is now ready to be transmitted. 

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