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Mobility Express DCA Channel selection problems

jmprats
Level 4
Level 4

I am using Mobility Express 8.10.112 with Dynamic Channel Assignment but it is not working as expected and I am experiencieng some problems and disconnections from clients.

Three AP's located one above the other on different floors are using the same 2.4 GHz channel. And clients sometimes are connecting  to AP's on differents floors. 

Previously I was using a WLC 5508 with those AP's and they selected 3 different channels

what can I do?

Thanks

18 Replies 18

pieterh
VIP
VIP

first you need to verify if on AP is functioning as master-AP (as controller) for the others? or are they working stand-alone?

second DCA does not allways mean different channels are selected. If there is little interference then same channel is a valid option.

third the WLC could have been tuned so DCA occurs on different parameters than the ME-controller  does.

 

Just to add, the RRM algorithm only works when three ap’s are in the required signal strength from each other. If for example floor 1 and 3 can’t reach each other, then RRM will not work. Having one ap in each floor, is fine as long as you have a small space in each floor, but to have ap’s in adjacent floors cover areas is at times a challenge. Take a look at your signal from each floor, use some free tools like WiFi Explorer or another tool that can scan the air and tell you what signal you see from the other ap’s while on different floors. This will give you and idea of the overlapping coverage, if you have any and also the useful signal from the adjacent access points if you have any. These tools will also show you the channel utilization which can help you see if the channels are fine that they are on or not. Dig around with tools so that you have a better understanding if there is really an issue or not. I think you would died more ap’s to get RRM to work however, but until you go and test, its just an assumption.
-Scott
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I have more AP's in each floor, but what it's strange for me is that those AP's  that are one below the other vertically on adjacent floors are on the same channel. And there are clients who detect both AP's (in adjacent floors) as the better signal and it seems this is creating some issues with the client performance.

 

This just happens since I migrated from WLC to Mobility Express. Before that all those AP's were in different channels

 

As I understand ideally the 3 AP's detected as best signal by a client should be in 3 non overlapping channels and that is not happening in some zones

Well I assume that all aps are on the same master AP? Also since you have other aps on each floor, then those are the strongest signal. The signal from adjacent floors are probably not as impacting that this adjacent. You are also talking about 2.4ghz, you only have three channels to use. Look at the signal the ap hears the ap on the adjacent floor at. 2.4ghz isn’t a good channel and your design should be to utilize 5ghz as much as possible. Your tax power on 5ghz should be 3-6db higher than on 2.4ghz. This only works if your design has enough 5ghz coverage everywhere. If not, then you are dependent on 2.4ghz which is not a good design these days. You also can manually set channels if you think that is the issue. Change the channels and see if users still complain, that will give you your answer if that is the cause of complaints.
-Scott
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Yes, I don't have enough 5 Ghz coverage so I turned it off.

I have noticed that at night the channel selection is more as expected, while during the day it changes. In this case it seems I have a bad channel selection because of my neighbours, do you agree?

So maybe is better to fix the channels in some AP's

Here is my opinion... you don’t have 5ghz coverage, tells me that the design is very sparse and probable old and has never been redesigned. To only have 2.4ghz these day’s is a poor choice as everyone has wireless enabled and there are more interference in 2.4ghz than on 5ghz. My suggestion is you leave 5ghz on, allow devices close to 5ghz coverage to connect and have 2.4ghz there to fill the gaps.
You need to assess your wireless coverage and if you want to have a good wireless network, you need to at least have -65 rssi with 25dbm of coverage on 5ghz everywhere with at least 20% cell overlap. If you have most or all of your AP’s in hallways for example, it’s time to look at a design where majority of your aps are in rooms and some in hallways for roaming.
-Scott
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I agree completely with that. I have most of my AP's in hallways and I need to have more in rooms.

Meanwhile, the problem  enabling 5 GHz now  is that there are devices that prefer a very bad 5 GHz connection than a good 2.4 GHz, so their experience is bad.

Well I think you need to assess that again. If client devices are still preferring 5ghz than 2.4ghz, it’s probably because of the utilization on the 2.4ghz being very high. So even if the signal is lower than the 2.5ghz, the 5ghz is still a better option. If users are looking at the signal bars and determining that it’s worse because of lower signal, that is incorrect. Use some free tools like WiFi Explorer to see the channel utilization and use iperf3 to test throughput on 2.4ghz vs 5ghz. That will help you determine what is better. If you really don’t have 5ghz coverage, make sure the tx power is set at 1 which is the highest and use the free tools to actually see what signal you get from within the rooms furthest away from the ap.
-Scott
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In my testing, Apple devices prefer connecting to a poor 5 GHz wifi than connecting to 2.4 GHz. And that creates a bad user experience if you don't have a good 5 GHz coverage. 

For me, it would be great if clients are able of choosing the best connection, but what I see it's that not always happens

Maybe I need to tune the configuration. Any help to configure 5 GHz with bad coverage? enable or disable lower rates? What about client load balancing? Maybe if I don't have a lot of clients it's better to disable load balancing because if not clients can roam to AP's with worse coverage. Band selection? Optimized roaming?

Part of any deployment is to tweak the system. However in your case, you have coverage gaps. So this is what you need to know. If you disable the lower data rates, that will tell the devices to roam when that data rate is no longer achievable. This will reduce your 5ghz coverage, but will give you a better experience in the edges of your cell. This goes the same for 2.4ghz. Remember on 5ghz you want to have the channel width at 40mhz, 20mhz is default for 2.4ghz. Makes sure the power in the 5ghz is at max or just set it at power level 1 since you know you have poor or no coverage in the edge of the rooms.
Again, you need to use a tool and investigate! Compare the channel utilization on both 2.4ghz and 5ghz. Manufacturers make their devices choose the best quality and again, 5ghz is less utilized than 2.4ghz. Don’t use load balancing.
-Scott
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Thank you very much.

What lower date rates do you recommend to disable?

You say "Remember on 5ghz you want to have the channel width at 40mhz", why? can be greater or automatic?

 

40mhz channel width gives you higher throughput than 20mhz. In production, you shouldn’t go higher than 40mhz unless you know for sure your aps will not be overlapping channels.
What data rate to disable is up to your “coverage”. I typically disable everything below 24mbps but you need to do testing to see if client can even connect when I the rooms. Adjust that lower to 18mbps if necessary. You can run a debug client and or set your laptop to 5ghz only and see where the laptop drops. That will give you a better understanding of your coverage area when tweaking your data rates and or power levels.
-Scott
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when I try to fix channel width to 40 MHz in Advanced - RF Optimization, I receive the message "At least One channel number should be selected" and "Error in IPAdress". And the channel Width remains in "Best"

You need to disable 5ghz network first unless you manually change per ap in which you have to set a channel and then apply before making channel width change. Might be easier to globally change from best to 40mhz.
-Scott
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