and 802.11ac standards allow sending multiple frames per single
access to the medium by combining the frames together into one
larger frame. There are two forms of frame aggregation: Aggregated
Mac Protocol Data Unit (A-MPDU) and Aggregated Mac Service Data
Unit (A-MSDU). CommView for WiFi can capture both types of
aggregated packets, as explained below.
A-MPDU frames are split into individual packets at the hardware
level. A-MPDUs can be up to 64 Kbytes in size. When an A-MPDU is
captured, it is passed to the application level as a number of
disaggregated packets that look like any other packets. These
packets are not marked by CommView for WiFi in any special manner.
Support for A-MPDUs is mandatory in the 802.11n and 802.11ac
standards. A-MPDU is widely used in 802.11n and 802.11ac devices.
A-MPDUs can be captured by any 802.11n or 802.11ac adapter that is
supported by CommView for WiFi.
A-MSDU frames are split into individual packets at the software
level. A-MSDUs can be up to 7,935 bytes in size. When an A-MSDU is
captured, it is passed to the application level as a single,
aggregated packet—i.e., in the form in which it was originally
received. If the aggregated packet is not damaged and if it can be
decrypted (if decryption is necessary), CommView for WiFi will
disaggregate the A-MSDU and will display the individual packets on
the packet list. Such packets will be marked as "Subframe #... of
A-MSDU #..." in the "More details" column. Additionally, the
subframes will be followed by the original aggregated A-MSDU, which
will be marked as "A-MSDU #...." If the aggregated packet is
damaged or encrypted, only the original A-MSDU will be displayed.
Support for A-MSDUs is optional in the 802.11n standard. A-MSDUs
are rarely used in 802.11n devices. A-MSDUs can be captured by the
following adapters that are supported by CommView for WiFi:
||Any recommended 802.11n PC
Card, ExpressCard, PCI, or PCIe adapters based on Atheros chipsets
and 802.11n USB adapters based on Ralink chipsets. A-MSDUs of up to
3,839 bytes are supported.
||Any recommended 802.11n
USB adapters based on Atheros chipsets and CACE Technologies
AirPcap adapters. A-MSDUs of up to 7,935 bytes are
||Any recommended 802.11ac
USB adapters based on Realtek chipsets. A-MSDUs of up to 7,935
bytes are supported.
large frames, such as A-MSDUs, are frequently damaged, especially
when being sent at high data rates.