- WiFi MAC architecture supports aggregation at two layers.
 - The MAC service data units (MSDUs) can be aggregated to form AMSDUs.
 - Each AMSDU serves as a single MAC protocol data unit (MPDU).
 - Another layer of aggregation is introduced when MPDUs can be packed together
 
(1) why aggregation is useful at all,
(2) why two layers of aggregation are useful,
Citation information:
G. Bhanage, "AMSDU vs AMPDU: A Brief Tutorial on WiFi Aggregation Support", arXiv preprint  arXiv:1704.07015, 2017.
Bibtex:
@article{bhanage2017amsdu,
  title={AMSDU vs AMPDU: A Brief Tutorial on WiFi Aggregation Support},
  author={Bhanage, Gautam},
  journal={arXiv preprint arXiv:1704.07015},
  year={2017}
}
