Any wireless 802.11ABGN Dual band USB adapters that correctly report N rates RRS feed

  • Question

  • I'm looking for a 802.11ABGN dual band USB adapter that fully supports netmon and correctly reports N data rates. I've tested the Belkin N600 DB adapter (Broadcom BCM4323 chipset) and it works well except when capturing N packets it reports low packet rates. 1.0 2.0, 6.5 14 53 are some common rates that I'm observing.  Other network monitors which use custom wireless drivers (and don't use NDIS) will show the actual rates on the packet that I would expect to see for 802.11n.

    I've investigated this issue by writing my own LWF driver and attached to it above the miniport.

    Ndis miniports report packet speeds using a single byte with units of 500 Mbit/s. When a LWF NDIS filter attaches to the miniport, the miniport passes it a data rate mapping table included in the NDIS_MINIPORT_ADAPTER_NATIVE_802_11_ATTRIBUTES struct. In theory this table should be used to translate the reported packet rate index (DOT11_EXTSTA_RECV_CONTEXT.usDataRate) to the actual rate by looking for this value in the DOT11_DATA_RATE_MAPPING_ENTRY.ucDataRateIndex and using the DOT11_DATA_RATE_MAPPING_ENTRY.usDataRateValue (2-byte word). This allows for reporting of the faster 802.11N speeds. For the standard ABG rates there is a direct mapping and the ucDataRateIndex is equal to the usDataRateValue.

    The Belkin adapter populates the data rate mapping table with all of the supported standard rates, and fills the table with additional entries which I presume are the N rates, but they have values in the usDataRateValue field that are a factor of 100x larger than the standard rates. 

    I guess I'm dealing with a miniport driver or firmware issue here.  Is there a USB dual band adapter that will give me the actual N rates on each packet?



    Tuesday, February 7, 2012 4:26 PM

All replies

  • We made some changes to the parsers so that we can correctly identify standard data rates.  For non-standard rates we display "Data Rate Cannot be Determined: Nonstandard Data Rate used".  You can get the latest parsers on http://nmparsers.codeplex.com which will hopefully address your issue.  If it does not, we might have to get some more details.



    Friday, February 10, 2012 2:08 PM