calculating transfer rate

[Varga Dávid]

Hi!

Thanks for your answer!
Although, I was aware of the things you mentioned (: I know how the tx rate
depends on SNR and BER theoretically.
The thing I want to find is that in practice where is it calculated or how
is it set in the hostap driver (in managed mode).

Thanks,
David


-----Original Message-----
From: hostap-bounces+varga.david=duvinet.hu at shmoo.com
[mailto:hostap-bounces+varga.david=duvinet.hu at shmoo.com] On Behalf Of
ahuguet at cttc.es
Sent: Monday, May 21, 2007 1:32 PM
To: hostap at shmoo.com
Subject: Re: calculating transfer rate

Hi David,

the transmission rate depends, indeed, on the signal to noise ratio, and
the desired BER (bit error rate) that has to be achieved.
The less SNR, the less transmission rate to keep a given BER.

As to where you can find the speed rate, I'll try giving you an answer,
although I've not tested that myself.

In the first place, the physical layer header contains information
regarding the transmission rate the payload is being sent at.
I'd say that you can get that information in the hostap driver code.
At the reception part, under void hostap_80211_rx()
there's an argument that is passed, rx_stats.
rx_stats->rate should contain the speed you're seeking.

Keep in mind that the number won't be 1 for 1Mbps, but 10. That's how the
standard 802.11b sets that field. So, expect to find 10,20,55,110.

Hope that's of help.

> Hello!
>
> Could anyone please tell me about the mechanism the driver uses to
> calculate
> the transfer rate for each packet?
>
> Does it depend on the recent received packet's signal and noise ratio?
>
> Is it even controlled by the driver or the firmware? If by the driver,
> where
> can I find it? (:
>
> Does the AP control the clients which speed they should use? If so, how
> does
> it work in ad-hoc mode?
>
>
>
> Thanks for the help!
>
> David
>
>
>
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