Imagine multiple railcars pulled by one train.
That’s what aggregate frames do for Wi-Fi.
A-MPDU
-Multiple MPDUs are combined together
-The MPDUs retain their own MAC header and FCS
-Delimiters are used before each MPDU
It’s like attaching multiple railcars on the same train engine.
A-MSDU
-Multiple MSDUs are combined together
-The MAC header and FCS are shared
-Each MSDU has a Sub-header
-Sub-headers contain L2 info (SA, DA, LLC etc.)
This is like putting freight destined to different places in the same railcar.
Keep in mind for aggregate frames:
-802.11ac and onward requires A-MPDU
-A-MSDUs must be in QoS Data frames
-A-MPDU and A-MSDU are often used together
When combined, there’s usually one A-MPDU with multiple A-MSDUs inside.
(A-MPDU was made for many MPDUs,
but nothing prevents it from just having one MPDU inside)
Want to see these in a pcap?
- For A-MPDU, use “radiotap.ampdu”
- For A-MSDU, use “wlan.qos.amsdupresent == True”
All aboard the aggregation express!
Which aggregation method do you see most often?
LinkedIn: 
[Wi-Fi Aggregation Explained: Railcars, Freight, and Frame Efficiency](🚂 Imagine multiple railcars pulled by one train. | Eva Santos