Hey Guido,
the problem using one radio is explained further here (from another company, but this applies to any WiFi mesh technology)
http://revolutionwifi.blogspot.com/2012/02/mesh-network-performance-impact.h...
Also, if you use two-radio nodes, make sure that you use one module on 2.4 GHz and one 5 GHz - if you use two modules in the same frequency band with omni antennas, even if you use separate channels (like 1 and 11), they may interfere with each other if the antennas are near to each other. There are quite a few ppl who can confirm this, e.g. check this:
https://hackerspace.be/Wbm2009v2/TestInterferenceResults
Possible Solutions: * use different bands * use directional or sector antennas * have a reasonable distance between your omni antennas
Cheers, Simon
On Wed, Mar 28, 2012 at 07:41:05PM -0300, Guido Iribarren wrote:
(this time i'll keep the mail short, insane details are attached as text :) )
Well, luckily for batman-adv devs, but unfortunately for me, the problem is in fact related to relaying between wlan interfaces in mr3x20 hardware (at least)
I understand this is not anymore batman related, but maybe someone has experience on this, or can point me into the right direction / maillist ? Given you have a good deal of equipments at the BattleMesh, maybe someone has already tried adding a wifi dongle and can confirm seeing this behaviour? (in a line of 2-radio nodes with static routing, packet throughput is halved on each hop)
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I've repeated the iperf tests in a controlled environment, this time using different subnets on each interface and static routes built with "route add". iptables flushed with -F and policy -P FORWARD ACCEPT no batman at all.
Packets coming in through wlan1 and out through wlan0 (or viceversa) experience (unexpected) "bandwidth degradation". Throughput drops from 30mbps to 15mbps (rough avg) The speed is closely comparable to using only 1 radio (packet comes in through wlan0, goes out through wlan0), so adding the dongle makes no net difference. (besides alternating the channel for transmission, throughput is halved over one hop anyway) 2 consecutive hops, alternating wifi radios, yield 1/3 throughput. (like it happens in a 1-radio mesh)
this does not happen if the packet comes in through eth0 and goes out through wlanX (or viceversa) . Throughput is maintained high at 30mbps.
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So the hardware (or kernel??) is uncapable of keeping up with the transfer speed *when two radios are involved*.
Has anyone bumped into a similar case, or has experience with these equipments? Maybe (again!) i am doing something wrong?
If this is confirmed, my only alternative to maintain good throughput along the mesh will be to install 2 x mr3220 on each node, connected back-to-back with ethernet cable. This will definitely work but the cost for each node owner evidently rises ;(
Thanks a lot!
Guido