Tx Rate Chosing
Anand S. Katti
askatti at ece.iisc.ernet.in
Tue May 25 07:44:44 EDT 2004
Is information exchanged about supported rates during Association is being
used in eventually settling to an initial TX rate for the connection ?
If yes, then what initial rate they settle on ?
Do they start with low rates and gradually ramp up ?
or they start with high value ?
In the function hostap_add_sta(struct ap_data *ap, u8 *sta_addr)
Some comments mention like this
/* No way of knowing which rates are supported since we
* get supported rates element from beacon/assoc req.
* that remote end supports all 802.11b rates. */
sta->supported_rates = 0x82;
sta->supported_rates = 0x84;
sta->supported_rates = 0x0b;
sta->supported_rates = 0x16;
sta->tx_supp_rates = WLAN_RATE_1M | WLAN_RATE_2M |
WLAN_RATE_5M5 | WLAN_RATE_11M;
sta->tx_rate = 110;
sta->tx_max_rate = sta->tx_rate_idx = 3;
Though im not good at coding but trying to understand hostap code. So need
Does this code mean that After assocaition(authenticated and associated)
the rate is fixed to 11MMbps ?
On Mon, 24 May 2004, Anand S. Katti wrote:
> Hello All,
> Kindly clear doubt of Probe Requests.
> Since probe request generation is handled in firmware I do not know
> In PROBE REQUEST PACKET FRAME:
> a) At what rate is this Probe Request Sent by the STA ?
> b) What initial rate does it choose ? in sendine probe Request ?
> c) In supported rates field does it include the STD specifed BASIC RATES
> only ? or does it actually calculates the SIR(if passive scanning) and
> includes the supported rates based on the SIR valueof the rxd beacon ?
> Any Answers will be helpful.
> On Sat, 22 May 2004, Anand S. Katti wrote:
> > >> When HostAP receives the Probe requests,
> > >It does not.. This is handled in firmware..
> > >> 0- does it fix the supported rates in the probe response based
> > >> on the SIR value ?
> > >> 0- does it fix the Tx Rate in the Association Response based on
> > >> the SIR value of the received Associate Request ?
> > >No.
> > Then How does the Firmware handle these probe requests and association
> > requests ?
> > I mean if the hostap is in sta mode, at what tx rate does the F/W send
> > the probe request/asso req ? does the f/w chose the tx rate by default ?
> > as highest 11Mbps or based on any other criteria ?
> > As far std says Generally control/mgmt frames are sent at 1 or 2 Mbps.
> > In Prism Driver Programmers manual F/w vers 2.3 its mentionde that f/w
> > keeps updated withthe channel info that contains signal and noise related
> > info, where else this SNR is used other than in AutoFallback Algo ?
> > Kindly answer.
> > Regards,
> > --Anand
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