Wi-Fi Aggregation Explained: Railcars, Freight, and Frame Efficiencyw

:steam_locomotive: 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”

:station: All aboard the aggregation express!

Which aggregation method do you see most often?

LinkedIn: :point_down:

[Wi-Fi Aggregation Explained: Railcars, Freight, and Frame Efficiency](🚂 Imagine multiple railcars pulled by one train. | Eva Santos