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The 802.11n standard allows 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.
Received 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 standard. A-MPDU is widely used in 802.11n devices. A-MPDUs can be captured by any 802.11n adapter that is supported by CommView for WiFi.
Received 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 802.11n PC Card, ExpressCard, PCI, or PCIe adapters based on Atheros chipsets. A-MSDUs of up to 3,839 bytes are supported. |
| · | Any 802.11n USB adapters based on Atheros chipsets and CACE Technologies AirPcap adapters. A-MSDUs of up to 7,935 bytes are supported. |
To check if the adapter is based on an Atheros chipset, please look at the list of supported hardware. If the "Supported OS" column reads "XP or higher," the adapter is Atheros-based.
Note that large frames, such as A-MSDUs, are frequently damaged, especially when being sent at high data rates.
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