[ath9k-devel] txop bursts issues

[ath9k-devel] txop bursts issues

[Claudio Pisa]

Hello, everybody.

I am working on a research project that uses the txop mechanism to
distinguish, on a 802.11b/g STA, between packet losses caused by
collisions and by noise.

I found some issues that are not clear to me on both mac80211 and ath9k,
but hopefully you can help.

The first one is the motivation behind commit
133a3ff2c934223a8143bfa52401bba962a97165, "cfg80211: allow setting TXQ
parameters only in AP mode". Is this just a temporary fix?
To get around this, and activate the txop functionality on a STA, I am
just hardcoding the burstTime (qi.tqi_burstTime = 102;) inside the
ath_txq_setup function in drivers/net/wireless/ath/ath9k/xmit.c

Then: is the duration field set by the hardware? We are using a D-Link
AR5008 NIC. It seems like the driver is always setting the duration to 0
due to (what I think is) a bug in net/mac80211/tx.c (line 154 function
ieee80211_duration):

     /* Don't calculate ACKs for QoS Frames with NoAck Policy set */
         if (ieee80211_is_data_qos(hdr->frame_control) &&
             *(ieee80211_get_qos_ctl(hdr)) |
IEEE80211_QOS_CTL_ACK_POLICY_NOACK)
                 dur = 0;

(i.e. using a bitwise or instead of a bitwise and) but then, sniffing
the frames, we find that the duration field is always set. However, this
duration field value seems not to be covering the subsequent ack and
transmission.

So I am wondering: is txop supported in ath9k? Or am I just doing
something wrong?

thank you and all the best,
Claudio

[ath9k-devel] txop bursts issues

[Claudio Pisa]

Hello.
Some updates follow inline.

On 05/24/2012 04:14 PM, Claudio Pisa wrote:
> I am working on a research project that uses the txop mechanism to
> distinguish, on a 802.11b/g STA, between packet losses caused by
> collisions and by noise.
> 
> I found some issues that are not clear to me on both mac80211 and ath9k,
> but hopefully you can help.
> 
> The first one is the motivation behind commit
> 133a3ff2c934223a8143bfa52401bba962a97165, "cfg80211: allow setting TXQ
> parameters only in AP mode". Is this just a temporary fix?

It looks like this is in the standard, as section "9.9.1.2 EDCA TXOPs"
says that "The TXOP limit duration values are advertised by the AP". Sorry.


> To get around this, and activate the txop functionality on a STA, I am
> just hardcoding the burstTime (qi.tqi_burstTime = 102;)

I rolled back these changes and configured the AP to advertise the
txoplimit duration values.

However, from our tests, the TXOP mechanism is still not working for the
setup ath9k+AR5008, while it works for other setups (madwifi+AR242x).
Is this a driver or just a hardware issue?


> Then: is the duration field set by the hardware? We are using a D-Link
> AR5008 NIC. It seems like the driver is always setting the duration to 0
> due to (what I think is) a bug in net/mac80211/tx.c 

I have submitted a (1 byte) patch to fix this:
http://marc.info/?l=linux-wireless&m=133820812304929&w=2

thanks and regards,
Claudio