2009/11/25 Benoit PAPILLAULT <benoit.papilla...@free.fr>:
> Benoit PAPILLAULT a écrit :
>> TX rate is dropping a lot (like 20 MBits down to 200 kbits/s). Using
>> another card in monitor mode, I still see packets sent at 54 Mbits rate
>> however.
> I found out what is wrong with the TX throughput. In fact, when a packet is
> transmitted at 54 Mbits, the destination send back a 802.11 ACK which is
> ignored!!! As such, the packet is transmitted at 54 Mbits once again, then
> twice at 48 Mbits, then twice at 36 Mbits ... and so on down to 1 Mbits. Of
> course, this divide the throughput by 18 (twice for each 9 rates), leading
> to 200 - 300 kbits.
> When implementing proper TX status reporting, needed by minstrel rate
> control, I also found out that some 802.11 ACK where not received by the
> driver, but received by the card, leading to inconsistencies in the rate
> control code.
> Are there some registers that are responsible for ACK behavior?
> Regards,
> Benoit

ACK handling and retrying is one of the known weak points of the
zd1211(b) chipset - apparently enabling CR_SNIFFER causes the card to
ignore ACKs received. Also, the retry plan for unACKed outgoing
packets (retry count & rates) needs to be uploaded to the device on
firmware init, and can't be controlled per-packet.

Luis: Any chance of an open firmware release for the ZD1211, similarly
to what was done for AR9170/ZD1221? That would probably allow for
fixing these problems.

Vista: [V]iruses, [I]ntruders, [S]pyware, [T]rojans and [A]dware. :-)

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