Re: [B.A.T.M.A.N.] FW: using Batman-adv

[Simon Wunderlich <sw@simonwunderlich.de>]

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Hi Joseph,

On Thursday 07 May 2015 13:00:52 Joseph Zimmer wrote:
> Hello,
>  
> I am working with BATMAN-ADV and have successfully setup a mesh. In my
> implementation of the mesh, the network requires BATMAN to operate in a
> linear topology and ideally have node 1 hop to node 2 then through node 3
> and finally node 4.
>  
>         Node1…………………….Node2……………………………..Node3…………………………Node4
>  
> In this network hops are preferred rather than distant links with low RSSI
> values(-70).  The problem that I’m seeing is that the protocol chooses
> routes that have the least hops but have RSSI values at about -78 to -90
> rather than routing through the closest node with RSSI values in the -50
> range.
>  
> We adjusted the hop penalty to a low value (we used 1 and 0) and we did see
> improvement with the hop selection but the throughput is very low due to an
> RSSI of -64 or less.
>  
> Questions:
>  
> 1)       Is there a way to adjust BATMAN using batctl to select routes based
> on the RSSI value?
> a.       That is, choose to hop through a node with an RSSI of -50 and never
> select a node that has a lower RSSI

Nope, BATMAN only uses packet loss as a metric. It could be possibly adjusted 
to do so or low signal links could be filtered otherwise, but we would consider 
that a bad hack.

There is another suggestion: You could increase the multicast rate to a high 
value, e.g. 36 MBit/s or even higher. Higher rates only work with good 
signals, and since batman-adv uses broadcasts (which is multicast for WiFi), 
this will have a direct effect on your network.

> 2)       Does the algorithm for route selection use RSSI in the calculation
> and if so can we modify the algorithm to increase the importance of RSSI in
> the selection?

It currently doesn't use RSSI

> 3)       How do we gain access to the code to make these modifications?

Batman-adv is open source, and so is mac80211 and hopefully the WiFi driver 
you use. However, it'd really suggest to start with tuning the multicast rate. 
:)

Cheers,
    Simon

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