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empwebs
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Very unusual wifi behavior on a 1,000 seater theater deployment using 9 GrooveA 52HPn, 2 SXT 2, and 1 wAP 2nD

Mon Sep 28, 2015 2:18 am

Hello,

I have been a Mikrotik user for more than 5 years now. I just have one of the most disappointing and frustrating experience that I want to share. This is a very strange incident and maybe you can share your thoughts on possible things that caused this in our event.

I have deployed a wireless network in a theater for a one day event. My backbone setup it this:
1. 3 ISP (total of 175Mbps) -----> connected to 3 ether ports of my CCR (CCR1036-12G-4S). (located in a data center)
2. CCR to the 3 IDF over fiber backbone of the building (using the 3 SFP ports on CCR)
3. on the IDFs - fiber to SFP is connected to RB 260GSP
4. RB 260GSP to a CRS (CRS210-8G-2S+IN) ------ theater location
5. CRS is connected to an HP Layer 3 switch
6. HP switch to 5 GrooveA 52HPn and others & 4 GrooveA 52HPn connected to the CRS

The setup of the Grooves and other APs are very basic, they are on home ap setup. Ether has as a static ip from the /16 network of the CCR and wifi is serving its own dhcp with a /22 network. Connection is routed to the CCR.

Wireless setup - 2.4Ghz, 20MHz, on separate channels, transmit power lowered to 8-10dBm. Each has its own SSID with their corresponding passwords...

When I'm on cable (connected to the CRS) - I can get a a full 175Mbps download. So I know that the connection from the data center to the theater area is rock solid. Have tested is for more than 3 days.

When all WiFi are setup, we tested each AP continuously and we consistently get a download speed of 20-30Mbps.

Now the event day. Minutes before the start of the event, we conducted the tests, and all APs have alteast 9Mbps of download speed. Our devices - laptop and mobile devices can easily connect to every AP. But when the event started, we noticed that majority of our users can't seem to find some APs' SSID, and those who can see the SSID are having a difficult time to connect. One MacBook pro of a presenter was having a hard time as well connecting even if the AP is just 2 meters away from the device, and when the device was able to connect, it can ping, it can resolve DNS, but wasn't able to browse on safari on all websites!

2 of my engineers are roaming the theater during the event, and they can't seem to connect to ALL of our APs. We tried to adjust transmit power to high, highest, low, lowest, we even tried to turn off all radios but 4 but still can't connect.

We really don't have any idea what happened.

The event on the theater was around 1PM to 530PM. Half-way through the event, I can see a few devices that are connected, but seem to get disconnected after a few minutes of connection. Then I tried to open my wifi analyzer in my android device. When I checked on the time graph (ssid strength over time) I saw this:
Screenshot_2015-09-26-15-56-53.jpeg
Screenshot_2015-09-26-16-02-16.jpeg
I was shocked to see that ALL wifi ssid seemed to stops in various intervals. Even SSIDs of radios that aren't ours! And from the graphs, it seemed to stop for a couple of seconds...

Then around 6PM, when the event was about to finish, I suddenly saw that one of our engineers who roamed the theater got a successful connection and a good download speed. Then I checked my analyzer again and saw a different behavior on the wifi time graph:
after-time-graph.PNG
I observed for more than 2 hours and still see the same behavior. No SSID is stopping and all devices can easily connect and can get a good download speed.

Also, just want to inform you that we also have 4 huawei AP6010 series and 4 Altai C1n, all have the same issue as the other Mikrotik APs.

Any thoughts please?
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uldis
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Re: Very unusual wifi behavior on a 1,000 seater theater deployment using 9 GrooveA 52HPn, 2 SXT 2, and 1 wAP 2nD

Mon Sep 28, 2015 3:55 pm

I suggest to use 5ghz as well as nowadays most of the new wifi devices support 5ghz as well and in 5ghz there are more channels which you can use at the same time and not disturbing other wifi networks.

What other hardware equipment were used during the event, maybe some other hardware was using 2.4ghz spectrum that made a big interference for the APs?
 
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BartoszP
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Re: Very unusual wifi behavior on a 1,000 seater theater deployment using 9 GrooveA 52HPn, 2 SXT 2, and 1 wAP 2nD

Mon Sep 28, 2015 5:32 pm

Blueteeth / Bluetooths ? Do not know correct form :-)
How many devices have you been serving ?
 
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Re: Very unusual wifi behavior on a 1,000 seater theater deployment using 9 GrooveA 52HPn, 2 SXT 2, and 1 wAP 2nD

Mon Sep 28, 2015 7:10 pm

i think the network has co-channel interference problem

use a spectrum analyzer to diagnose

sorry you had problems with your wifi

2.4ghz spectrum its hard to manage because there only 3 non overlapping channels
 
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Re: Very unusual wifi behavior on a 1,000 seater theater deployment using 9 GrooveA 52HPn, 2 SXT 2, and 1 wAP 2nD

Mon Sep 28, 2015 9:36 pm

So you instaled all this in the same room/hall or more than two in the same room?
Allow me to :lol:
 
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Re: Very unusual wifi behavior on a 1,000 seater theater deployment using 9 GrooveA 52HPn, 2 SXT 2, and 1 wAP 2nD

Tue Oct 06, 2015 8:27 am

Here is your answer:
Image

You can't install 12 APs on 2.4GHz in same place as it was already mentioned, there are only 3 non overlapping channels. If there are other APs around its even worse..

Your WiFi analyzer shows a complete mess, nothing would work in that environment.
 
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Re: Very unusual wifi behavior on a 1,000 seater theater deployment using 9 GrooveA 52HPn, 2 SXT 2, and 1 wAP 2nD

Thu Oct 08, 2015 12:42 pm

So you instaled all this in the same room/hall or more than two in the same room?
Allow me to :lol:
With all due respect, I don't think there is anything to laugh at it. Everyone learns a lot of things the hard way.
As a bad experience as it is, it is nice it was shared so other will know what not to do.
 
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Re: Very unusual wifi behavior on a 1,000 seater theater deployment using 9 GrooveA 52HPn, 2 SXT 2, and 1 wAP 2nD

Thu Oct 08, 2015 2:45 pm

Dense deployments are tricky things. As bad as this turned out, hopefully you've manage to learn a lot and made some good observations.

Key points (some as mentioned above):
2.4G has only 3 non-overlaping channels 1 - 6 - 11 (some countries you may also get 14 but it's close to 11)
In the UK we have Bands A (5150-5350MHz) and B (5470-5725 MHz) in 5GHz for serving STA's (other countries vary)
This give us 19 non-overlapping channels (DFS, Max EIRP, TPC, Radar and other factors apply)
Most modern devices can do Dual Band

In crowded events you have no control over rogue AP's, people wirelessly tethering, other non WiFi 2.4GHz devices being operated, number of devices people may bring and try to use on your network etc etc, the list goes on.

Anything essential (presenter pc's, front of house, ticketing etc) hard wire it in, or use backhaul channels / bands that are not used for client connections to bridge connections and provide a final hard wired connection.

Don't give WiFi away to the masses on mass unless you have to. If you do, plan well and tests heavy.

I've found it better to provide good, low power (multi AP's, 5.8 + 2.4, different channels, same ssid, client numbers limited and access policy to detach those below a set signal level, you can also disable lower data rates or MCS) coverage in smaller areas of an event where people numbers can be controlled by the environment, this way people move to those areas to use the WiFi then move away when finished. This way you can provide a good, fast connection without devices needlessly leeching on any available AP.

Better for you and better for them, but, this strategy wont work for every type of event or venue.
 
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Re: Very unusual wifi behavior on a 1,000 seater theater deployment using 9 GrooveA 52HPn, 2 SXT 2, and 1 wAP 2nD

Thu Oct 08, 2015 8:07 pm

its a high density scenario, take a look on this guide

http://www.cisco.com/c/en/us/products/c ... 93245.html
 
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Re: Very unusual wifi behavior on a 1,000 seater theater deployment using 9 GrooveA 52HPn, 2 SXT 2, and 1 wAP 2nD

Fri Oct 09, 2015 8:57 pm

Thank you all for replying! Yes, indeed this is big lesson for us! We really tried our best and we were challenged (forced) to provide internet to all participants.

I think the main issue really was there was a unnecessary interference - intentional or accidental... Something caused our radios to stop every few seconds... Which I don't think interference would cause. Also, there were Huawei APs that have 5Ghz radio that wasn't affected by what happened.

Some lessons here: better preparation and load testing, use of dual band radios, limit wireless users as air space can only be divided as much...

Thanks again!
 
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Re: Very unusual wifi behavior on a 1,000 seater theater deployment using 9 GrooveA 52HPn, 2 SXT 2, and 1 wAP 2nD

Fri Oct 09, 2015 9:04 pm

By the way the idea really is to provide a lot of APs with low transmit power so as not to heavily overlap the available channels. Users were given their corresponding AP's SSID and password to manage AP usage per section/area of the theater...

But when issues arise, we tried to change the settings, raising tx power, and even turning off most of the radios just to see if its an interference issue coming from the 16 radios... There was a point where only 4 radios were on, but still no improvement....

Also another very weird thing is that one of the backup plan is to provide a Huawei LTE Modem router with WIFI as a backup connection, then when we tried it on wire, download speed reached 40Mbps, but again our laptop cannot connect directly to the wifi of that device even if we're just beside it!
 
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Re: Very unusual wifi behavior on a 1,000 seater theater deployment using 9 GrooveA 52HPn, 2 SXT 2, and 1 wAP 2nD

Mon Oct 12, 2015 8:20 pm

I have done wireless deployments in conference centres so I have some experience with this kind of thing!

Just a wee FYI, in most of the world, and if you can do without supporting 802.11b, you can potentially use 4 channels in the 2.4GHz range, 1, 5, 9 and 13, rather than 1, 6 and 11. How well this actually works will depend on whether there are a lot of other busy networks in the air; if all around you is 1, 6 and 11 which you can do nothing about, you will do better to use those channels and have your APs co-operate with the neighbours, rather than using overlapping channels and shouting over each other.

As for location, I would have spread them evenly around the room, going in sequence through whichever set of channels, and used just one SSID - you get better diversity this way. Then tune (turn down) the power on the APs til the ones on the opposite side of the room are noticeably lower than the near ones. In this case I would have preferred aerials with zero gain rather than the GrooveA 52HPn's 6dB gain ones.

And yes, go dual-band, and configure those 5GHz radios with narrow (20MHz) channels. You will get more actual throughput for hundreds of clients using 4 radios on separate 20MHz channels than you will if the same 4 radios are all on the same 80MHz channel, because you massively reduce losses through collisions.

Thanks for the link to the Cisco guidance, I must have a proper read :D
 
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Re: Very unusual wifi behavior on a 1,000 seater theater deployment using 9 GrooveA 52HPn, 2 SXT 2, and 1 wAP 2nD

Wed Oct 14, 2015 1:13 pm

Sorry, just realised those Groove APs are 2.4/5GHz switchable... so next time, use 3 in 2.4GHz channels 1, 6, and 11, and 6 in 5GHz, all different channels, e.g. 36, 40, 44, 48, 52, 56, and use 2 SSIDs, one 2.4GHz and one 5GHz, tell people to use the 5GHz SSID if they can see it, you should be fine!
 
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Re: Very unusual wifi behavior on a 1,000 seater theater deployment using 9 GrooveA 52HPn, 2 SXT 2, and 1 wAP 2nD

Wed Oct 14, 2015 1:56 pm

I have done wireless deployments in conference centres so I have some experience with this kind of thing!

Just a wee FYI, in most of the world, and if you can do without supporting 802.11b, you can potentially use 4 channels in the 2.4GHz range, 1, 5, 9 and 13, rather than 1, 6 and 11. How well this actually works will depend on whether there are a lot of other busy networks in the air; if all around you is 1, 6 and 11 which you can do nothing about, you will do better to use those channels and have your APs co-operate with the neighbours, rather than using overlapping channels and shouting over each other.
in the case of my country most client devices only support 1-11 channel by regulation

here is a old test using 4 channel with worst results than 3 channel (channel 1 throught 11), maybe with 13 channel the things will be different

some times its better to have co channel interference than adjacent channel interference because co channel interference cause contention, adjacent channel interference cause retransmissions and that is worst

http://wiki-files.aircrack-ng.org/doc/o ... hannel.pdf
 
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Re: Very unusual wifi behavior on a 1,000 seater theater deployment using 9 GrooveA 52HPn, 2 SXT 2, and 1 wAP 2nD

Wed Oct 14, 2015 11:17 pm

... you will do better to use those channels and have your APs co-operate with the neighbours, rather than using overlapping channels and shouting over each other.
... some times its better to have co channel interference than adjacent channel interference
Yes, that is what I meant, even if I put it badly :)
 

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