Re: Not reaching optimum speeds with IEEE 802.11n

[Sourav <sourav.chakraborty@netcommwireless.com>]

Hi All,
Is there a parameter in hostapd.conf or elsewhere to enable/disable MPDU 
and MSDU aggregation? Please reply as this is very urgent.

Thanks in advance,
Sourav
On 12/09/14 18:00, Sourav wrote:
> On 12/09/14 17:46, Helmut Schaa wrote:
>> On Fri, Sep 12, 2014 at 4:11 AM, Sourav
>> <sourav.chakraborty@netcommwireless.com> wrote:
>>> On 11/09/14 00:14, Helmut Schaa wrote:
>>>> On Wed, Sep 10, 2014 at 10:42 AM, Arend van Spriel 
>>>> <arend@broadcom.com>
>>>> wrote:
>>>>> On 09/10/14 03:26, Sourav wrote:
>>>>>> We are using Ralink chip Rt3072L (using rt2800usb drivers 
>>>>>> rt2800usb.c),
>>>> The Ralink USB hardware is quite bad in reporting TX status and as
>>>> such minstrel_ht cannot do proper rate selection.
>>>> If you watch the rc stats at
>>>>
>>>> /sys/kernel/debug/ieee80211/phy0/netdev\:wlan0-0/stations/xx:xx:xx:xx:xx:xx/rc_stats 
>>>>
>>>> you might see a lot of rate selection "hopping".
>>>>
>>>> Regards.
>>>> Helmut
>>> please take a look at the attachments.... the first one shows the 
>>> rc_stats
>>> and iperf stats side by side on the router(iperf is running in 
>>> client mode
>>> in the router).....the second attachment is from a laptop which is 
>>> running
>>> iperf in server mode.
>>>
>>> I don't see a lot of rate "hopping" in the rc_stats file, (T,t and 
>>> P) rates
>>> are pretty much stable.... yet there is a big difference between 
>>> those rates
>>> and the throughput using iperf......
>> Indeed, rc_stats looks acceptable.
>>
>>> when you say "Ralink USB hardware is quite bad in reporting TX 
>>> status", do
>>> you mean that the HW reports less tx rate to minstrel_ht and so its 
>>> rate
>>> calculation is screwed up?
>> The HW sometimes does not report the status of transmitted frames 
>> correctly.
>> The TX status register is a FIFO of 16 (or similar) elements and if
>> the driver is
>> not reading it "fast enough" the FIFO will overflow :( at least that
>> was the point
>> when I was looking at the ralink hardware last time. Not sure if 
>> something
>> changed recently.
> How did you detect this? I can see no error messages in 
> syslog....hence I am thinking that the HW is processing packets 
> properly....though I may be wrong here.
>>> Can you please let me know the section of code inside 
>>> Rc_80211_minstrel_ht.c
>>> (or somewhere else) which deals with getting the tx rate from ralink 
>>> HW?
>> There is no special code in minstrel(_ht) in regard to rt2x00.
>>
>> Are you able able to get some statistics on the receiver side (your
>> windows machine)
>> regarding TX rates and AMPDU lengths?
> the 2nd attachment had logs from the windows machine.....it is also 
> showing similar rates as on the router
>> Helmut
>
>


-- 
Warm Regards,
Sourav


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