[Battlemesh] [B.A.T.M.A.N.] Batman-adv high TQ and Low throughput

cmsv cmsv at wirelesspt.net
Wed Apr 30 16:24:00 CEST 2014

Inline reply

On 04/24/2014 05:48 AM, Simon Wunderlich wrote:
>> Recently i have experienced something quite usual to my experience and
>> that was not happening previously in the same scenario where it is
>> happening now.
>> Here is the example:
>> 2 nodes at with adhoc at 2.4ghz at a distance of 415 meters
>> one uses an omni 15 dbi antenna at 18dbi and another 24 dbi grid at 16 dbi.
>> This link was previously providing up to 21 mbit being 17 mbit a the
>> lowest. Batman-adv TQ value was always around 230 being many times above
>> 250.
>> However this has recently changed the same link with 230~250 TQ and the
>> same txpower is now outputting 1.93 Mbits/sec
>> I have used iperf for bandwidth tests. Batman-adv version is 2013.4.
>> Although i have considered several types of scenarios that can be
>> causing this issue i have also tested against some which leaves me
>> puzzled in regards to the presented TQ quality and dBm values as the
>> nodes dBm are sometimes bad (ie: -80 ~ -90)
>> One of the main questions is: shouldn't batman-adv TQ reflect or be
>> influenced by dBm values ? How come with -90 dBm i get batman-adv to
>> show me 230 TQ ?
> The current implementation in batman-adv counts broadcast packets to compute 
> the TQ. Therefore this number reflects (more or less) the transmit success 
> probability on whatever wifi broadcast modulation rate you have configured 
> (default the lowest, e.g. 1M in 2.4 GHz). A common tweak is to set the 
> broadcast rate (also called multicast rate) to something higher, e.g. 18M or 
> 36M, to get a better analysis on these modulation rates. This should also help 
> in your scenario, but might affect the range of your batman-adv network.

> what's the mcast_rate value?
> having 230~250 TQ on a -80/-90dBm link seems like you have a very low mcast_rate.

I did try change the mcast_rate as well as the rate and while at first
it did show some gains the same did not maintained after a few days.

dbm levels and throughput have not changed and in fact in a few cases my
throughput got worse.

I tried with 36000 as well as 6000

I am now believing 2 possible scenarios:

1: Software/driver problems or bug
a) big or weak support that only came into effect after playing wit
firmware settings. (re-flashing the routers without new or the same
firmware should clear this doubt)

2: Interference caused by:
a) weather conditions that have changed since the nodes lost huge
performance levels.
b) Although i am able to have the local community cooperation by having
them changing their home routers to non overlapping frequencies i wonder
how much of it can be caused by the network nodes and their co-existent
channels. Then again this does nto explain why the loss of performance
did not happened right away after the network upgrade.

However all these possibilities do not answer the fact that these nodes
worked flawlessly for some time and one day overnight  the problem happened.

c) deliberate interference caused by some possible competitor. although
i cannot be sure at this moment; i see it as the biggest possibility.

In the past this has led me to look for this:
which keeps me thinking about Wi-Spy + Chanalyzer or equivalent if any.

Which i am currently, once again very included to do and
suggestions/alternatives are welcome as well as wanted.

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