Non destructive scanning while connected to current AP.

Andrea G Forte andreaf
Mon Feb 28 08:11:02 PST 2005

It seems that everytime a handoff occurs, the STA sends Null function 
packets to the AP, one at the beginning of the scanning process and one 
at the end of the scanning process. These packets tell the old AP when 
to start and stop buffering packets for the STA. I had a thread earlier 
on the meaning of these frames and Jouni explained what I just told you. 
However, these packets can introduce a significant delay in the handoff 
process. This means that even though the packets are buffered, if the 
delay introduced by these null function frames is too big, the buffered 
packets are useless (at least for VoIP and other real-time applications).
It would be better to not have them at all when using real-time 
applications. Unfortunately these frames are controlled by the firmware 
and not the driver.
Furthermore if you read the 802.11 standard the particular mechanism 
that takes care of buffering is "out of the scope" of the standard, so I 
am not sure if using the null function frames is the "standard" way to 
do it.


Ajeet Nankani wrote:

> I want to know that when a STA is connected to AP and is actively 
> transferring and receiving data from AP, and during that when STA 
> tries to scan network non-destructively then what happens to current 
> data transfer while scanning, because for scanning, channel needs to 
> be changed for active probes, so what happens with the current data 
> frames from current channel?
> are they lost? or buffered at STA and at AP both? and if buffered, do 
> STA indicates AP to buffer frames by sending PS frame to AP or some 
> other procedure?
> -ajeet.
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