Re: i have a question ? How many relay nodes can be supported at NetworkCoding ( mtu 1546 ) .

[johnzeng <johnzeng2013@yahoo.com>]

Hello Dear Sven and Martin:

                                              Thanks for your advisement

                                              I hope to aviod Excavation 
of underground pipeline in the smart community or Park .

                                              if Batman-adv can support 
smart relay ( networking code ) at mesh network really , and it will be 
very valuable for us .

                                              i think one of  core 
valuable point is  relay mode   and   Client roaming

                                              i prepare to build more ap 
evironment and test for the part  later




As market competition intensifies,

                                              the gap between similar 
productsis getting smaller and smaller,

                                              likewise the evolution of 
growing homogenization trends within the industry.



                                              i hope we can find 
valuable point for Blue Ocean each other .

                                              if you have some different 
point , and I would be happy to be the first and build win-win mode each 
other .


                                              Best Regards

                                               Tiger





> Hi,
>
>> When i compile the part , whether i need make
>> CONFIG_BATMAN_ADV_BATMAN_V=y at batman-adv-2016.2
> 2016.2 is "old". And BATMAN_V has nothing to do with network coding.
>
>> i read some detail about NetworkCoding , my understanding :
>>
>> every relay node will detects neighbors packet at promisc mode and
>> combine these packet into a single transmission ,
> I think Martin can help here. He also provided some documentation:
>
> * https://www.open-mesh.org/projects/batman-adv/wiki/NetworkCoding
> * https://www.open-mesh.org/projects/batman-adv/wiki/NetworkCoding-technical
> * https://downloads.open-mesh.org/batman/papers/batman-adv_network_coding.pdf
> * https://vbn.aau.dk/da/publications/catwoman(214ee21a-e786-495d-85c9-3efac4718ead).html
> * https://downloads.open-mesh.org/batman/misc/wbmv4-network_coding.avi
>
> And it will not try to forward each packet is overheard. Instead it
> will try to find coding opportunities which it then uses to forward
> its own packets in less transmissions (by using packets which the
> other nodes should already know).
>
>>                batctl nc 1
>>                echo 1 > /sys/class/net/bat0/mesh/network_coding
>>                ip link set dev wlan0 promisc on
>>                ip link set dev wlan0 mtu 1546
> Your cards/drivers will most likely not even support promiscuous mode.
> Some of them require to have an monitor mode interface at the same time and
> some of them will simply not work.
>
> You can test it by simply checking what tcpdump is showing you on the
> underlying interface (wlan0). If it doesn't show you the packets between
> two other nodes then promiscuous mode is not working for you.
>
> The feature itself is not used very often (Martin, please correct me here).
> It is not enabled by default because it is not making things "better" all
> the time [1]. So it is also not tested as much as other components in
> batman-adv and you should think first if it is really useful for your
> scenario/HW. I knew at least from some Freifunk communities played around
> when it was enabled by default but had to revert when they experienced "non
> functional mesh links" (nothing more about it is known to me - sorry Martin).
>
>
>> if i send a packet from host A to hostC via hostB, whether hostB will
>> open relay mode at layer2 .
> I completely failed to parse this.
>
> batman-adv will send your data from hostA to hostC via hostB when the TQ
> value for the link "from hostA to hostC via hostB" is higher than the TQ
> value for the link "hostA to hostC directly". This has nothing to do with
> network coding and is a standard feature of batman-adv (this is actually
> what it is about).
>
> network coding can only (when lucky) try to combine some packets - but
> this will only work when promiscuous mode is actually working and the
> nodes can overhear packets. Otherwise it will (in theory - Martin please
> correct me if I overlooked a safety mechanism) just create a lot of coded
> packets which cannot be decoded anymore. This seems to be especially
> problematic when some nodes are for example 2x2 MIMO devices and others
> are 3x3. At least this would be a good way to let the 2x2 miss important
> packets when the 3x3 devices talk between each other.
>
> I would even guess that things like dynamic transmission power would make
> overhearing packets also more problematic.
>
>> but i have a question ? How many relay nodes can be supported at
>> NetworkCoding ( mtu 1546 ) .
> I am not sure what you are asking here. The implementation in batman-adv
> can combine two packets into one. And this combining of these two packets
> is done by exact one relay node. The decoding is done by the two receiving
> nodes. What you can build with it is been shown in the documentation from
> Martin. The network coding used here is therefore done by a relay node and
> its neighbors. But there can be multiple relay nodes in the mesh doing
> network coding at the same time.
>
>
> I personally haven't used network coding with batman-adv. But since you've
> created multiple new threads on the mailing list [1,2,3,4] (beside the
> private mail *grml*) - here is at least a pseudo-answer.
>
> Kind regards,
> 	Sven
>
> [1] https://www.open-mesh.org/projects/batman-adv/wiki/NetworkCoding#Drawbacks
> [2] https://lists.open-mesh.org/pipermail/b.a.t.m.a.n/2016-November/016586.html
> [3] https://lists.open-mesh.org/pipermail/b.a.t.m.a.n/2016-November/016587.html
> [4] https://lists.open-mesh.org/pipermail/b.a.t.m.a.n/2016-November/016588.html
> [5] https://lists.open-mesh.org/pipermail/b.a.t.m.a.n/2016-November/016592.html