Ed Okerson wrote:

On Thu, May 5, 2011 at 12:35 PM, Sven Eckelmann sven@narfation.org wrote:

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Ed Okerson wrote:

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On Thu, May 5, 2011 at 10:44 AM, Marek Lindner lindner_marek@yahoo.de

wrote:

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Hi,

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We are evaluating using Batman in an environment where there could be 200-300 devices in a single building. We started out setting up 10 devices in our office to figure out how everything works and do some throughput testing. We have noticed that the routing decisions always send the packet to the node towards the destination with the highest signal strength. This causes the packet to always traverse the network with the maximum possible number of hops, which causes performance to degrade quickly. Is it possible to use a different routing algorithm? It would seem that sending to the node closest to the destination that the source node can still communicate with directly would minimize the number of hops.

if you wish to minimize the number of hops you have to increase the hop penalty. Check the "hop penalty" section here: http://www.open-mesh.org/wiki/batman-adv/Tweaking

That seems to indicate that it is a per node setting, i.e. "using this node will incur a penalty of x". That is also not the desired behavior. For our installation all nodes are in a fixed location, so using a particular node as a next hop in the route may incur a penalty for one source node, but not another. This should be dynamically determined for each route from each source to each destination to minimize hops.

So you have to increase the hop penalty everywhere to force the routing algorithm to reduce the number of hops and prefer worse routes with less hops.

If I increase the hop penalty on all nodes, they will all still be equal. If all nodes have a hop penalty of 128, will it not make the same routing decisions as it does if they are all 10?

No, the wiki explains it quite well, but I'll try to explain it a little bit different. Lets assume that you have perfect links (quality = 255) between all nodes in a route. Each one would say: "hey, I can reach the following neighbors with the quality of 255".... now introduce a penalty in each hop (10 for example) which is just substracted from the incoming value. So after a distance of 5 hops only a quality of 205 would be announced. Therefore a node with only a distance of 2 (quality = 235) would be prefered as next hop in this case and not the one with the distance of 5.

Target - X1 - X2 - X3 - X4 - X5 - (Announces route with quality 205 to Target) \ \ Y1 - Y2 - (Announces route with quality 235 to Target)

This is a quite abstract and not 100% correct explanation of the hop penalty, but should help to understand the implications a little bit better. You have to do the calculations yourself to find a good value for hop penalty.

You should have a look at send.c to find more information about it. You should see that it is not really substracted in a linear fashion and that the actual quality is calculation is also more complex,... but the idea is similar to the example mentioned before.

Kind regards, Sven