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WirelessRudy
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NV2 sync works but destroys performance

Wed Aug 16, 2017 3:55 pm

Maybe on a short post I'll get some replies... :(

2 SXT-SA's side by side (1 mtr. vert. distance) covering both their sector.
Both work fine. One with 8 clients, the other with 24. (All SXT)

When the NV2 sync is setup according Wiki the sync works, but CCQ collapse and download to clients falls from 30-40Mb to an low 3-8Mbps.!

Tried several minor config variables but all the same. In sync mode the P2MP network collapses.

Anybody with other/better experiences, please share yours.
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Rudy R. Puister

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Re: NV2 sync works but destroys performance

Wed Aug 16, 2017 9:14 pm

Can you check with the snooper the clients signal from the other AP?
 
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soulflyhigh
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Re: NV2 sync works but destroys performance

Wed Aug 16, 2017 10:57 pm

Can you check with the snooper the clients signal from the other AP?
That is most probably the cause for performance-drop issue.
All the CPEs from one AP simply MUST have very good isolation from other AP(s) and vice versa. If sync could work on different channel (as we know now is working only within APs on the same channel) then this wouldn't be a problem.

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M.
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WirelessRudy
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Re: NV2 sync works but destroys performance

Thu Aug 17, 2017 3:12 am

I forgot to mention my extended post for the same matter; viewtopic.php?f=7&t=124499
Here it is explained what the setup and performance test was.
All the CPEs from one AP simply MUST have very good isolation from other AP(s) and vice versa.
Well, imho the whole Idea of running two AP's (or more) is that there is no more interference between the AP's on the same tower in the same frequency.
The AP sends and all stations listen, the stations can then send when the AP's are listening.

Off course now it could be that a client of AP1 while transmitting his signal will hit AP2. And vice versa, client of AP1 while in receiving mode might also receive signal from AP2.
We only have to hope that client only communicates with its designated AP's signals and not the other.
With Mikrotik SXT it is almost impossible to have 'very good isolation' between the signals of both AP's.

An SXT that sits 100 meter away from AP1 and is designated to pick its signal, will also pick a signal from AP2 on the same tower even if that AP might be directed in the opposite direction.
The question now is more, what S/N distance (or pure signal difference) will client get/send to AP1 compared to AP2? Is 6dB enough? (twice the signal), 10dB?, 20? 30 or more? What level are we seeking for to be considered as a good 'isolation'?

I could imaging replacing the two SXT APs' with two netmetals and RF elements horns for a 'very high isolation' at the tower. But that would then only work in an 'open field' scenario. In an urban environment there will be signal reflections and bouncing so SXT-CPE A sending signal to AP1 will still 'hit' the AP2 it is not associated to. Due the sync this AP will pick this signal! And that can be pretty strong!
Some clients can be located close to the edge of one AP's signal sector and thus also close to the border of the next AP. If they are both in sync, the signal difference between the two AP's from or to that client is marginal, no matter for instance the ftb ratio of the AP's or the limited side lobs.
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Rudy R. Puister

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Re: NV2 sync works but destroys performance

Thu Aug 17, 2017 4:21 pm

WirelessRudy, I agree with everything you said, and I don't think that Mikrotik's sync will be a viable solution for p2mp in the current form.
Cheap CPEs are radiating in various directions significant amounts of RF energy and in urban environment reflections are causing even lower SNR.
We're using RF covers for SXT SA5 APs to improve their f/b ratio and that helps in certain degree but we're still not using sync because of the current technological limitations.

P2p links with high gain and high f/b ratio should work reasonably good on the same channel.

I really hope they'll find a way to sync APs on different channels because I don't see any way to isolate something like SXT or LHG in a real world and mass scale (thousands of CPEs).

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M.
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Re: NV2 sync works but destroys performance

Thu Aug 17, 2017 4:43 pm

 
WirelessRudy
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Re: NV2 sync works but destroys performance

Thu Aug 17, 2017 5:24 pm

I have a couple of these. Not connected to the specific AP's for the test though. I was so enthusiast in the finding of a sync with MT I just picked a tower and tried to use it.
I believe these shields work, but in fact never have seen any real measurements of the effect.
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Re: NV2 sync works but destroys performance

Thu Aug 17, 2017 11:47 pm

With any shield one side to reflect unwanted signals and the other side to absorb ( not reflect ) which to date I must admit i haven't seen any so far.
 
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Re: NV2 sync works but destroys performance

Fri Feb 23, 2018 9:48 pm

I've asked to MK support the reason of this drop, they said that clients that are more than one AP are going ti have problems.
This feature isn't very useful, I always fine costumers that are more APs from the same tower.
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