Modifying the Interframe Spacing

Gaurang Ramesh Naik gaurang at
Wed May 25 19:11:01 PDT 2016

Hello Michal,

I have been trying what you suggested. First, I manually programmed
the value of AIFS in the mac.c file. Then I adjusted the aifs values
in the hostapd.conf file at the AP. I forgot to mention in my last
post (not sure if it is relevant though)- I am using Openwrt at the AP
as well as client.

Now for the testing part: If I set the aifsn for some AC to a large
value (say 200), the aifs must be extremely large (order of 1-2
milliseconds). This is what I expect, but not what I am observing. I
tried using ping with the different tos values. However, for different
tos I get similar ping values. Am I missing something obvious here? Is
ping a correct way to even check this?

One more thing - I was reading the hostapd config file. When you said
I can adjust aifs from the config file, I assume you meant changing
the "tx_queue_data3_aifs" parameter, and that is what I changed. Now,
there is also this parameter "wmm_ac_bk_aifs" which, as per the config
file, is supposed to be "These parameters are sent to WMM clients when
they associate. The parameters will be used by WMM clients for frames
transmitted to the access point". Does this mean the aifs value set
using mac.c is overridden by this hostapd parameter? Or am I
understanding this incorrectly? I tried setting this value to 200 as
well. But again, ping values for different tos were similar.

Thanks for your previous response. Although I did not get the effect I
wanted, but I got to try many new things. Any new suggestions are


On Fri, May 6, 2016 at 3:09 AM, Michal Kazior <michal.kazior at> wrote:
> On 6 May 2016 at 00:15, Gaurang Ramesh Naik <gaurang at> wrote:
>> Hello,
>> I am working on a research project as a part of which I need to modify
>> the interframe spacing value (specifically the difs) of all 802.11ac
>> nodes (AP as well as STAs) in my test network. In one of the research
>> papers, I read that by changing the AIFSN in ath5k drivers, the
>> authors had changed the AIFS value. I have been trying to see where
>> this has been implemented in the source code under the ath/ath10k/
>> directory. Could someone please assist me with the following
>> questions,
>> (i) Is such a thing even possible in ath10k?
>> (ii) Am I looking in the right place (in the ath10k directory)?
> FWIW You can influence AIFS via WMM parameters, at least on AP this
> should be configurable via hostapd conf file. For client mode you'll
> have to override the value programmed in ath10k_conf_tx() in mac.c
> Not sure if it'll do what you expect it to though. Could be worth checking out.
> Michał

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