[B.A.T.M.A.N.] Unterstanding gateway-mode - why do nodes have a "sticky" gateway

Jan Lühr ff at stephan.homeunix.net
Wed Jan 16 12:38:09 CET 2013


Hello world!

I'm back:

Am 16.01.2013 um 02:42 schrieb NicoEchániz:

> I wanted to share this proposal we arrived at after discussion with some AlterMundi hackers, so we can discuss it during our future IRC session. I've previously shared it with yanosz, who had some observations that he can better explain, but agreed on this initial assumption which triggered the proposal:

I'll be available on IRC this evening (20:00 CET) - sadly, I'ven't found any other contributers in our freifunk-community?

> 
> The scenario we see in our networks is that over a certain link quality which is considered acceptable, we want the clients to choose the gw with better bandwidth. So if for example this quality floor is TQ 100, then if a gw has 6Mbit/s advertised b/w and another has 3Mbit/s, the clients that see this gateways with a TQ above 100 will choose the faster one between them.
> 
> 
> We observed that in the current implementation, advertized gateway throughput is used to modify the final gw selection by publishing unrealistic bandwidth. The proposal tries to fix this, as well as the "dynamic switching" for selection class 1. Looking at the current code involved we also believe it would allow to make the implementation simpler.
> 
> 
> This would be the proposed options:
> 
> gw_sel_class [1,2]
> 1 will consider gw throughput, 2 will only consider TQ. When using selection class 1, clients will switch gateways if one with better throughput becomes available and reachable with a TQ above gw_tq_floor (see below). Defaults to 2.
> 
> gw_tq_floor
> Only relevant for gw_sel_class 1. Above this TQ floor, the gw with the
> best advertised throughput will be chosen.* Defaults to 100(?)
> 
> gw_tq_threshold
> TQ delta that triggers a gw switch in the client. If gw_sel_class is 1,
> the tq_threshold will only be considered to choose between two or more
> gateways advertising the same winning throughput on the net. Defaults to 20.

Well - I still think, that having a fixed gw_tq_floor may cause unstable gateway-selections if tq oscillates around gw_tq_floor.
Perhaps we can discuss this in detail.

Thanks,
Keep smiling
yanosz


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