[wpa_supplicant] Is there a way to limit peers (to about 12) for IBSS/adhoc?

[Xuebing Wang <xbing6@gmail.com>]

Hi community,

This email is mainly addressed to hostap/wpa_supplicant mailing list.

Descriptions of my issue:
- I am establishing IBSS/adhoc network using OpenWRT 15.05 + ath9k (AR9331).
- When nodes are relatively closely placed, the peers (the term is 
'neighbors' in batman-adv mesh) reach 40, ath9k driver detects "tx hung, 
resetting the chip" (for RESET_TYPE_TX_HANG).
- This ath9k "tx hung" randomly happens among the 40 nodes (in adhoc 
network), and it happens relatively often (seemingly randomly for 
nodes), and randomly makes some nodes un-usable.
- This appears to be an issue with ath9k kernel driver or ath9k hardware 
that it can not handle ~40 peers.
- IBSS/adhoc with 20 peers work well.

Is there a config in wpa_supplicant that we can limit the number of peers?

In the other words, once the number of peers ('iw wlan0 station dump') 
reaches a pre-configured number (e.g. 12 or 16), wpa_supplicant does not 
authenticate any more, for IBSS/adhoc only?
- A subtle detail: once a new beacon with higher RSSI is detected, the 
current connection with lowest RSSI will be de-authenticated, and to 
authenticate this new peer (with higher RSSI in beacon).

Is this "limiting number of peers for IBSS/adhoc" a good work-around for 
40+ peers adhoc network, although the ultimate root cause seemingly is 
with ath9k kernel driver or ath9k hardware?

Also, if there are many (like 40+) peers in IBSS/adhoc network, I am not 
sure how medium access contention and collisions factor in, for 
management frames?

Here is my wpa_supplicant conf file:
------
ctrl_interface=/var/run/wpa_supplicant

# use 'ap_scan=2' on all devices connected to the network
# this is unnecessary if you only want the network to be created when no 
other networks are available
ap_scan=2

network={
     ssid="Net-xxxxxxxx"
     mode=1
     frequency=2462
     proto=WPA2
     key_mgmt=WPA-PSK
     pairwise=CCMP
     group=CCMP
     psk="xxxxxxxx"
}
------

Another approach could be to use user-space shell script to "iw <dev> 
ibss leave" for the lower RSSI stations?
- As I am using batman-adv to build mesh network on the top of 
IBSS/adhoc, a similar approach can be done at batman-adv level.

Suggestions?

Thanks.
Xuebing Wang


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