Re: [B.A.T.M.A.N.] mcast_rate setting of wifi interface has significant effect to performance of V. Re:Re: Recent test result. Re:Re: Paper "Performance Evaluation of BATMAN-adv Wireless Mesh Network Routing Algorithms "

[Sven Eckelmann <sven@narfation.org>]

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On Montag, 3. September 2018 12:03:07 CEST Ligang LIU wrote:
[...]
> I'm continuing to test in my deployment and has found an interesting thing:
> The mcast_rate setting of wifi interface has significent effect to performance of V,
> while it does not affect batman-adv IV too much.
> 
> config wifi-iface 'default_radio1'
>         option mcast_rate '18000'
>         ......
> 
> I generated the wireless configuration in web page and there is no mcast_rate setting for adhoc mode. When I noticed the line "option mcast_rate '18000'" in the batman-adv wiki page, I tried to set mcast_rate and repeated the test. I find that, with mcast_rate setting, batman-adv IV will get some performance improvement, and the performance of batman-adv V has significantly improved.

Still sounds like something is eating away airtime. Just changing the 
multicast rate here will just make more room for other frames since the 
multicast/broadcast packets take less time to get transmitted. There are other 
effects on the amount of multicast/broadcast packets which will be lost 
(interesting for B.A.T.M.A.N. IV) but I would guess that we can ignore that at 
the moment.


Did you investigate what is the problem here? Did you play around with the ELP 
interval? Did you check the RTS/CTS durations? Did you find anything else 
which eats too much airtime when you compare B.A.T.M.A.N. IV and B.A.T.M.A.N. 
V? Is the higher ELP broadcast interval (compared to B.A.T.M.A.N IV OGM 
interval) to blame here or the ELP unicast probes?

> I'm now trying to understand how the mcast_rate affects the performance of the adhoc network. If more tests can verify the importance of this setting, I so suggest that it should be highlighted for the end users of the batman-adv, especially for the new ones. For the OpenWRT system, if mcast_rate can be automatically set for the adhoc mode, or the related web page can explicitly provide a user interface  to set mcast_rate in adhoc mode, it should be more end user friendly.

Please get in touch with the OpenWrt LuCI developers [1] about the OpenWrt 
"webpage" configuration. We cannot really help you here.
 
> I hope my tests can be helpful to improve the batman-adv V and your comments and suggestions are appreciated.

Since it is not clear at the moment why it happens, we cannot do anything on 
our end.

Kind regards,
	Sven

[1] https://github.com/openwrt/luci/
    http://luci.subsignal.org/trac

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