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A technician has set me up the wireless bridge between two houses but I have problem with ping under load.

I have two MikroTik RB/SXTG devices in server/clint mode. They see each other (no obstacle) and distance is only about 20 meters. The issue is that pings under load are in hundreds of miliseconds.

I have already tried to update version 6.24 and reboot. I tried also change the frequency to auto and it seemed fine for while. Any idea?

See screenshots with configuration.

server client

banterCZ
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    If a network gets busy, ping times increase, especially on a shared medium like Wifi. – Sven Jan 12 '15 at 19:37
  • @sven I do not think that this is typical times increase, because the AP inside the other house works much better. And I am speaking just about pings to device, not to the internet. – banterCZ Jan 12 '15 at 21:17
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    SXTs and other similar routerboards are NOT for indoor use. If your signal is too high then the cards will not be able to play nice. You should decrease the tx-power and put the SXTs further away from each other. You need at most a -55dB signal in order to be able to pass traffic without problems. Other than that there are numerous things that might cause you increased latency. It's difficult to say without further information. – Cha0s Jan 13 '15 at 14:27
  • @Cha0s Indeed, there are out. So you are saying that they are too close? – banterCZ Jan 13 '15 at 14:35
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    You said 20meters so I assumed that you were trying to use them indoors. If the signal is too high then essentially you cannot use them. The cards will 'overflow' and won't be able to pass traffic. You need to get the signal at least down to -55 to be able to pass traffic properly. – Cha0s Jan 13 '15 at 15:08
  • @Cha0s The most probably it was caused by the technician, because has set different protocol at each AP (Nv2-nstreme-802.11 and just 802.11). I will double check that, but it seems much better so far. – banterCZ Jan 14 '15 at 09:59
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    @banterCZ regardless of the protocol if the signal is too high you won't be able to pass traffic properly. You need at the most a -55dB and your signal is at +16dB (!) according to your screenshots. It just won't work properly with such strong signal. Don't take my word for it, ask at the Mikrotik forums and you will get the same response. – Cha0s Jan 14 '15 at 11:25
  • @Cha0s Could you transfer your comments to the answer, I would like to accept it. – banterCZ Jan 14 '15 at 11:55
  • Unfortunately the question is on-hold so I cannot answer to it. Did lowering the signal help? – Cha0s Jan 14 '15 at 11:57
  • @Cha0s I will contact supervisors. The original TX power was 17 dbm. I have lowered it to 0 and the chart is much better now. I also tried some negative values but I do not see the difference. – banterCZ Jan 14 '15 at 20:45
  • @Cha0s It's reopened now. Go ahead and post the answer. – HopelessN00b Jan 14 '15 at 21:08

1 Answers1

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According to your screenshots the signal is too high and in SXTs and similar routerboards, if there is too high signal then the wireless card's amplifier gets over-driven resulting in bad quality link essentially.

You need to lower the tx-power on both sides so that the signal drops at the most to -55dB.
Others say it should be -65dB but I've seen SXTs and other similar routerboards work just fine at -55dB. Anything higher though results in a bad link with high latency and bad throughput.

This is a common issue, at least with Atheros 802.11n cards such as AR92XX, AR9300. (AFAIK it's not software related).
Older 802.11a cards (such as CM9 - Atheros AR5213) do not show this problem.
I've had links at -40dB working just fine on 802.11a.

Now, as a bonus to this answer, you can use nstreme on both sides instead of regular 802.11 protocol.
This will boost your total bandwidth significantly and reduce the latency during high data transfers.
http://wiki.mikrotik.com/wiki/Manual:Interface/Wireless#Nstreme

Another trick to boost and stabilize your link is to use specific data-rates (configured on the AP side) since your link is ptp (point to point).
This helps the wireless driver since it will not have to constantly recalculate the quality of the link and what rate to use.

And finally, you can check the quality of your link with the 'CCQ' metric. http://wiki.mikrotik.com/wiki/Manual:Wireless_FAQ#What_is_CCQ_and_how_are_the_values_determined.3F

As long as CCQ is at 100%/100% (tx/rx) then your link will most likely perform at its best.
If CCQ drops bellow 80-75% then you will see some degradation or even disconnects.

Keep in mind that CCQ is calculated based on the packets passing through the link.
So if you have little or no traffic you will see pretty much random numbers.
Don't panic, it's normal. Just start a bandwidth test (tools > bandwidth test) between the 2 SXTs with both send/receive traffic (UDP only, since TCP is too heavy for routerboards) and you will start seeing the normal CCQ numbers.

Cha0s
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