In my trace I can see few of probe responses until authentication request is sent. I was wondering why probe Request /Response takes around 3 seconds when there's good signal between the client and the AP, while authentication Req/Resp and association Req/Resp packets take few mili seconds. The client is using ubuntu and iwconfig with the Ap's MAC address specified asked 14 Dec '11, 03:19  ddayan edited 14 Dec '11, 03:26 showing 5 of 9 show 4 more comments |
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do you see multiple probe requests before the probe response or is it just one probe request followed by probe response?
Yea I can see multiple probe requests, the client sits next to the AP.
please check for the R-bit being set in 802.11 header for layer2 retransmissions if inside any of those requests. Is there a ~ 3 second delay between the last probe request and the probe response?
nope delay is around 0.05 seconds
so I guess thats the probe request to which the AP responds by sending the probe response. Check the ones that were sent before for the Retransmission bit, that would explain everything
no retransmission bit, because probe request is a Broadcast packet...
sorry my bad - of course you're right... anyways I would guess that the last probe request was the first to really get processed by the AP thus making the delay only those 0.05 sec you mentioned. No clue why the ones before got lost or whatever
I guess a trace from the AP would shade some light on this. However even after a probe response, another probe request is sent. Is it because the linux drivers wait to see if they can find a better AP?
probe request are in any way sent out frequently - independent on your machine connecting or not connecting to a certain AP. In most cases that's the driver "preprobing" every visible SSID, so that certain parameters are already known either for faster connection or just for informational reasons e.g. displaying more information about the available APs in the GUI