finding signal quality for bridging/STP over WDS from a Master

Greg Johnson gregfjohnson at yahoo.com
Mon Jun 16 11:38:26 EDT 2003


First, congratulations on the hostap project - this is a fanstastic
piece of work!

A question - how can I find point-to-point signal quality between multiple
hostap-enabled Linux boxes all operating under WDS and all in Master mode?

I am using WDS and bridging.  In order to use STP (either the one that
comes with the bridging software, or perhaps a user-space roll-your-own),
I would like to be able to weight the edges of the connectivity graph
based on signal quality.

But I can't tell how to determine signal quality between two (or N)
wlan's operating in Master mode.

As a simple example, say I have three boxes, server_a, server_b, and server_c.
Server_b is physically between server_a and server_c, and (let's say) the
signal quality reflects this fact.  (server_a sees server_b much more
strongly than it sees server_c, and similarly server_c sees server_b much
more strongly than it sees server_a.)

So, under this scenario, I would like to do the following:

on server_a:  iwpriv wlan0 wds_add server_b_mac
on server_b:  iwpriv wlan0 wds_add server_a_mac
              iwpriv wlan0 wds_add server_c_mac
on server_c:  iwpriv wlan0 wds_add server_b_mac

But, I would like software to be able to decide the above, based on detection
of signal quality among the boxes.  Furthermore, I would like to dynamically
re-test signal quality every once in a while, and adjust the graph if
necessary based on changes in the RF environment.

How can I do that?

One thing that might work is to have each of the wlan's temporarily drop
out of Master mode to Managed mode one at a time, peek around at the
other wlan's in Managed mode to get signal quality to the N-1 Masters
nearby, and then go back into Master mode itself.

Under that scenario, if there are actual clients attached to that AP,
would it be possible to somehow not disassociate those clients while doing
this hack?

If it is not doable at the moment based on the driver software, I'd be
interested at having a go at modifying the software to make it possible.

Does this sound sane/reasonable/possible to the gurus of the hostap software?

(It looks like signal quality is only obtainable in Managed mode.
In hostap_ioctl.c, in the function hostap_get_wireless_stats, I notice
a block of code


        if (local->iw_mode != IW_MODE_MASTER &&
            local->iw_mode != IW_MODE_REPEAT) {
                    struct hfa384x_comms_quality sq;

                    ...
        }
)

Thanks a million for any comments or suggestions,

Greg Johnson

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