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Tweaking beacon interval and minimum rates

 
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westbywest
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Joined: 16 Dec 2008
Posts: 320
Location: St. Louis, MO USA

PostPosted: Wed Feb 13, 2013 8:39 pm    Post subject: Tweaking beacon interval and minimum rates Reply with quote

Hi All,

I was recently pointed to this this neat presentation from David Lang, and Intuit employee, about deploying large-scale wifi access.
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Besides configuring madwifi to no serve very low birates (e.g. 1Mbit/s) and chew up airtime, David also had the clever tip to set wifi beacon intervals to a prime number like 997ms instead of 1000ms. That would (in theory) help prevent wifi clients from becoming inadvertently synchronized in their housekeeping traffic, and help smooth out usage of the spectrum. Cool!

To do this in ROBIN v3842, you could change /lib/robin/endboot/12_madwifi to be the following:

Code:
#!/bin/sh

vaps="ath1"
[ "$(uci get mesh.Myap.up)" -eq 1 ] && vaps="${vaps} ath2"

MCAST=$(uci get madwifi.priv.mcast_rate)
[ -n "$MCAST" ] && {
        logger -st ${0##*/} "set ath0 mcast_rate to $MCAST"
        iwpriv ath0 mcast_rate $MCAST
}

logger -st ${0##*/} "set abolt=0 and doth=0 for $vaps"
for VAP in $(echo $vaps) ; do
        logger -st ${0##*/} "set abolt=0 and doth=0 for $VAP"
        iwpriv $VAP abolt 0
        iwpriv $VAP doth 0
done

MINRATE=$(uci get madwifi.priv.minrate)
[ -n "$MINRATE" ] && {
        logger -st ${0##*/} "set ath0 minrate to $MINRATE"
        iwpriv ath0 minrate $MINRATE
        logger -st ${0##*/} "set ath1 minrate to $MINRATE"
        iwpriv ath1 minrate $MINRATE
}

BINTVAL=$(uci get madwifi.priv.bintval)       
# set default 100ms beacon interval               
[ -z "$BINTVAL" ] && {                             
        BINTVAL=100                               
}                                                 
logger -st ${0##*/} "set ath1 bintval to $BINTVAL"               
iwpriv ath1 bintval $BINTVAL                                     
                                                                 
distance=$(uci get madwifi.priv.distance)                         
[ -n "$distance" ] && sysctl -w dev.wifi0.distance="$distance" >&-
#


Then you can add bintval and minrate options to /etc/config/madwifi as such:
Code:
config madwifi priv
   option skip 0
   option mode ahdemo
   option frag 2346
   option rts 256
   option rate auto
   option distance 2100
   option mcast_rate 5500
   option wmm 0
   option doth 0
   option abolt 0
   option bintval 997
   option minrate 5500
#


... and reboot the node.

I've verified these setting don't immediately knock repeater nodes offline, but that's about it. Caveat Emptor. Furthermore, long beacon intervals are not ideal for situations where you want to connect lots of battery-powered devices, or clients that roam b/w nodes frequently. For them, try shorter prime intervals like 373ms.

Of the 4 nodes where I applied these settings, one particular node with a history of poor throughput yet decent RSSI saw some very mild throughput improvement. But, these weren't nodes in a particularly dense mesh.[/code]
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