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Highlighted
Beginner

High Channel Utilization in High density Environment

Hello, 

I'm seeing a high channel utilisation on our APs in a high density environment with lots of APs being deployed to cope with capacity. The lower date rates have been disabled. We've only enabled 18Mbs and above on the 5GHz only but using only channel 36,40,44 and 48 channels since we are close to the airport to avoid DFS.

 

But the APs are still seeing each other considerably even though they are operation on the lowest power (Level 6) and we have few channels to work with.

 

Will disabling 18Mbs  reduce the APs from seeing each other and will it help in bringing down the channel utilisations????

 

thanks

 

 

13 REPLIES 13
Highlighted
Beginner

The high channel utilisation is seen on some of these APs with few clients (13clients) connceted to them.

 

And with RX-SOP help in any way of bring the utilization down???? Right now the Rx-Sop is on default settings.

Highlighted

RX-SOP can help but that will reduce the CU from what the AP hears not with what a client or tool will show. You can disable more data rates. I have set some environments at 48mbps as mandatory and 54 and 36 as supported with the lowest tx power. If your limited to only 4 channels then you are also limited by what you can do. CU and client experience will vary and you should test that yourself and get feedback from others.
-Scott
*** Please rate helpful posts ***
Highlighted
Beginner

Hi ,

 

Scott has mentioned a valid point and I resonate with what he has mentioned. However, in this case , I would like to go back to the initial problem.

What is the WLC code ? AP model ? Where are you seeing the channel utilization ? and what is the value ?  Can u paste the output of "show ap auto-rf 802.11a/b <AP name>" for any one AP ?

 

Rx-SOP is kind of asking your AP to "don't pay heed to signals below x dBm" which may not solve the high channel utilization that you are seeing here. However, it may help to solve any roaming issues in a HD environment. There are a couple of bugs around false channel utilization. Hence, let's first focus on the software and hardware environment.

 

Cheers,

Manish 

Highlighted

Thanks for replies guys.

 

Its version 8.2.141.0 using 5520 WLC and the APs are 3702i series. the channel utilisation varies but with few clients 16clients and atimes 8 clients on two APs, I am seeing Channel utilisation of 45% and 53% respectively . This tends to go a lot higher when it gets busy with clients, it can go over 65% CU.

 

Due to dry and glass walls which has low attenuation, the APs tend to see each other quick easily, hence the suggestion if more data rate to shrink the cells and prevent the APs from seeing each other less.

 

show ap auto-rf 802.11a 000C04-012

Number Of Slots.................................. 2
AP Name.......................................... 000C04-012
MAC Address...................................... 84:b2:61:c0:c2:d0
Slot ID........................................ 1
Radio Type..................................... RADIO_TYPE_80211a
Sub-band Type.................................. All
Noise Information
Noise Profile................................ PASSED
Channel 36................................... -94 dBm
Channel 40................................... -94 dBm
Channel 44................................... -95 dBm
Channel 48................................... -94 dBm
Channel 52................................... -96 dBm
Channel 56................................... -94 dBm
Channel 60................................... -95 dBm
Channel 64................................... -93 dBm
Channel 100.................................. -96 dBm
Channel 104.................................. -97 dBm
Channel 108.................................. -98 dBm
Channel 112.................................. -98 dBm
Channel 116.................................. -98 dBm
Channel 132.................................. -97 dBm

--More-- or (q)uit
Channel 136.................................. -98 dBm
Channel 140.................................. -97 dBm
Interference Information
Interference Profile......................... PASSED
Channel 36................................... -128 dBm @ 0 % busy
Channel 40................................... -128 dBm @ 0 % busy
Channel 44................................... -128 dBm @ 0 % busy
Channel 48................................... -128 dBm @ 0 % busy
Channel 52................................... -128 dBm @ 0 % busy
Channel 56................................... -128 dBm @ 0 % busy
Channel 60................................... -128 dBm @ 0 % busy
Channel 64................................... -128 dBm @ 0 % busy
Channel 100.................................. -128 dBm @ 0 % busy
Channel 104.................................. -128 dBm @ 0 % busy
Channel 108.................................. -128 dBm @ 0 % busy
Channel 112.................................. -128 dBm @ 0 % busy
Channel 116.................................. -128 dBm @ 0 % busy
Channel 132.................................. -128 dBm @ 0 % busy
Channel 136.................................. -128 dBm @ 0 % busy
Channel 140.................................. -128 dBm @ 0 % busy
Rogue Histogram (20/40/80/160)
.............................................
Channel 36................................... 0/ 0/ 0/ 0

--More-- or (q)uit
Channel 40................................... 1/ 0/ 0/ 0
Channel 44................................... 0/ 0/ 0/ 0
Channel 48................................... 0/ 0/ 0/ 0
Channel 52................................... 0/ 0/ 0/ 0
Channel 56................................... 0/ 0/ 0/ 0
Channel 60................................... 0/ 0/ 0/ 0
Channel 64................................... 0/ 0/ 0/ 0
Channel 100.................................. 0/ 0/ 0/ 0
Channel 104.................................. 0/ 0/ 0/ 0
Channel 108.................................. 0/ 0/ 0/ 0
Channel 112.................................. 0/ 0/ 0/ 0
Channel 116.................................. 0/ 0/ 0/ 0
Channel 132.................................. 0/ 0/ 0/ 0
Channel 136.................................. 0/ 0/ 0/ 0
Channel 140.................................. 0/ 0/ 0/ 0
Load Information
Load Profile................................. PASSED
Receive Utilization.......................... 0 %
Transmit Utilization......................... 0 %
Channel Utilization.......................... 72 %
Attached Clients............................. 14 clients
Coverage Information
Coverage Profile............................. PASSED

--More-- or (q)uit
Failed Clients............................... 0 clients
Client Signal Strengths
RSSI -100 dbm................................ 0 clients
RSSI -92 dbm................................ 0 clients
RSSI -84 dbm................................ 0 clients
RSSI -76 dbm................................ 0 clients
RSSI -68 dbm................................ 2 clients
RSSI -60 dbm................................ 6 clients
RSSI -52 dbm................................ 6 clients
Client Signal To Noise Ratios
SNR 0 dB.................................. 0 clients
SNR 5 dB.................................. 0 clients
SNR 10 dB.................................. 0 clients
SNR 15 dB.................................. 0 clients
SNR 20 dB.................................. 0 clients
SNR 25 dB.................................. 1 clients
SNR 30 dB.................................. 2 clients
SNR 35 dB.................................. 7 clients
SNR 40 dB.................................. 1 clients
SNR 45 dB.................................. 3 clients
Nearby APs
AP 2c:33:11:1a:41:60 slot 1.................. -65 dBm on 116 20MHz (172.23.141.245) 000C04-008
AP 84:b2:61:6e:29:90 slot 1.................. -72 dBm on 40 20MHz (172.23.141.245) 000C04-021

--More-- or (q)uit
AP 84:b2:61:be:71:90 slot 1.................. -54 dBm on 44 20MHz (172.23.141.245) 000C04-010
AP 84:b2:61:c6:fe:f0 slot 1.................. -58 dBm on 36 20MHz (172.23.141.245) 000C04-020
AP 84:b2:61:c7:08:20 slot 1.................. -63 dBm on 116 20MHz (172.23.141.245) 000C04-018
AP 84:b2:61:c7:08:50 slot 1.................. -76 dBm on 36 20MHz (172.23.141.245) 000C04-004
AP 84:b2:61:c7:9a:e0 slot 1.................. -59 dBm on 48 20MHz (172.23.141.245) 000C04-009
AP 84:b2:61:c8:21:c0 slot 1.................. -42 dBm on 116 20MHz (172.23.141.245) 000C04-013
AP 84:b2:61:c8:65:b0 slot 1.................. -64 dBm on 40 20MHz (172.23.141.245) 000C04-017
AP 84:b2:61:ce:2c:90 slot 1.................. -61 dBm on 64 20MHz (172.23.141.245) 000C04-019
AP 84:b2:61:cf:89:e0 slot 1.................. -69 dBm on 48 20MHz (172.23.141.245) 000C04-022
AP 84:b2:61:cf:91:40 slot 1.................. -73 dBm on 44 20MHz (172.23.141.245) 000C04-005
AP 84:b2:61:d1:35:40 slot 1.................. -50 dBm on 44 20MHz (172.23.141.245) 000C04-014
AP 84:b2:61:d1:36:c0 slot 1.................. -43 dBm on 116 20MHz (172.23.141.245) 000C04-011
AP 84:b2:61:d1:36:e0 slot 1.................. -70 dBm on 40 20MHz (172.23.141.245) 000C04-006
AP 84:b2:61:d1:37:50 slot 1.................. -53 dBm on 48 20MHz (172.23.141.245) 000C04-016
AP 84:b2:61:d1:3c:40 slot 1.................. -61 dBm on 36 20MHz (172.23.141.245) 000C04-015
AP 88:1d:fc:26:22:c0 slot 1.................. -74 dBm on 48 20MHz (172.23.141.245) 000GA16
AP 88:1d:fc:48:0b:30 slot 1.................. -76 dBm on 140 20MHz (172.23.141.245) 000GA22
AP 88:1d:fc:57:dd:70 slot 1.................. -71 dBm on 44 20MHz (172.23.141.245) 000GA21
AP 88:1d:fc:57:e3:b0 slot 1.................. -64 dBm on 40 20MHz (172.23.141.245) 000GA20
AP b0:aa:77:7b:96:f0 slot 1.................. -69 dBm on 40 20MHz (172.23.141.245) 000CA11
AP b0:aa:77:7b:b2:b0 slot 1.................. -71 dBm on 60 20MHz (172.23.141.245) 000CA12
AP c4:0a:cb:5c:32:70 slot 1.................. -76 dBm on 52 20MHz (172.23.141.245) 000W2A3
AP c4:0a:cb:5c:7b:80 slot 1.................. -76 dBm on 40 20MHz (172.23.141.245) 000B2A3

--More-- or (q)uit
AP c4:0a:cb:5c:7d:10 slot 1.................. -74 dBm on 44 20MHz (172.23.141.245) 000B4A3
AP c4:0a:cb:5c:82:80 slot 1.................. -73 dBm on 44 20MHz (172.23.141.245) 000B1A3
AP c4:0a:cb:5c:85:80 slot 1.................. -73 dBm on 36 20MHz (172.23.141.245) 000B1A1
AP c4:0a:cb:64:54:c0 slot 1.................. -72 dBm on 40 20MHz (172.23.141.245) 000C01A4
AP c4:0a:cb:64:57:70 slot 1.................. -68 dBm on 44 20MHz (172.23.141.245) 000B3A3
AP c4:0a:cb:64:5e:70 slot 1.................. -65 dBm on 36 20MHz (172.23.141.245) 000BN4A3
AP d4:a0:2a:9b:5a:b0 slot 1.................. -74 dBm on 36 20MHz (172.23.141.245) 000C2A3
AP d4:a0:2a:d0:6a:20 slot 1.................. -72 dBm on 48 20MHz (172.23.141.245) 000C3A3
Radar Information
Channel Assignment Information
Current Channel Average Energy............... -55 dBm
Previous Channel Average Energy.............. -55 dBm
Channel Change Count......................... 46
Last Channel Change Time..................... Wed Jan 3 03:00:17 2018
Recommended Best Channel..................... 48
RF Parameter Recommendations
Power Level.................................. 6
RTS/CTS Threshold............................ 2347
Fragmentation Threshold...................... 2346
Antenna Pattern.............................. 0

Persistent Interference Devices
Class Type Channel DC (%%) RSSI (dBm) Last Update Time

--More-- or (q)uit
------------------------- ------- ------ ---------- ------------------------
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(WH01) >?

 

Highlighted

You can try to disable more data rates but that only allows devices to connect to a specific AP if the client can negotiate at that rate. CU will happen all the way out to 1mbps since you only have 4 channels that you are using, your CU should be as high as the 2.4ghz to be honest. We have sites in APAC that only can use 4 channels also and you just try to get it down as much as you can and then there is not much more you can do. We have tested applications with CU of 75%+ with no user complaints. Now user experience varies from site to site or in different regions of the globe. So do what you can to make it usable. That’s what I do and the only thing you can do.
If your focus is to lower it more, then you will have to shut some radios off. Don’t know if that’s what you want to do.
-Scott
*** Please rate helpful posts ***
Highlighted

Hi Wales,

 

Thanks for the output. First of all I am surprised to see that the Rx and Tx utilization is 0 even when you have 14 clients attached to this AP. and still the CU is 72%. :) When we move down in this output , we can notice that more than 2 APs are being heard very loud on the same channel which this AP is working on. This is basically co-channel interference (CCI).  If this is the case on radio 1 , I can imagine the situation on Radio 0.

Now, as Scott mentioned , the reason may be that too many APs are deployed in this area. U may be aiming for an HD deployment when u did the site-survey. I am not sure. But going with the number of clients on the APs , I don't think it's an HD deployment. Thus, my recommendation would be to try with turning off a few radios strategically (going with the floor plan and obstacles). See if that helps. I hope that it should.

Cheers,

Manish

Highlighted

I back his suggestion. Based on the amount of clients per AP (if the number should stay below 20), disable some radios.
Even though you are close to an airport, you might want to check if they really use all DFS frequencies for radar. If not (which is probably the case) you might get 1-10 additional channels to use without disturbing the airport/having outages from the AP changing the channel. Anyway, based on the neighbors you have to many APs. An alternative would be to use external, directional antennas (if the AP permits external ones).
I've sorted your table a bit different, to make it better readable:
84:b2:61:c6:fe:f0 -58 dBm 36 20MHz 000C04-020
84:b2:61:d1:3c:40 -61 dBm 36 20MHz 000C04-015
c4:0a:cb:64:5e:70 -65 dBm 36 20MHz 000BN4A3
c4:0a:cb:5c:85:80 -73 dBm 36 20MHz 000B1A1
d4:a0:2a:9b:5a:b0 -74 dBm 36 20MHz 000C2A3
84:b2:61:c7:08:50 -76 dBm 36 20MHz 000C04-004

84:b2:61:c8:65:b0 -64 dBm 40 20MHz 000C04-017
88:1d:fc:57:e3:b0 -64 dBm 40 20MHz 000GA20
b0:aa:77:7b:96:f0 -69 dBm 40 20MHz 000CA11
84:b2:61:d1:36:e0 -70 dBm 40 20MHz 000C04-006
84:b2:61:6e:29:90 -72 dBm 40 20MHz 000C04-021
c4:0a:cb:64:54:c0 -72 dBm 40 20MHz 000C01A4
c4:0a:cb:5c:7b:80 -76 dBm 40 20MHz 000B2A3

84:b2:61:d1:35:40 -50 dBm 44 20MHz 000C04-014
84:b2:61:be:71:90 -54 dBm 44 20MHz 000C04-010
c4:0a:cb:64:57:70 -68 dBm 44 20MHz 000B3A3
88:1d:fc:57:dd:70 -71 dBm 44 20MHz 000GA21
84:b2:61:cf:91:40 -73 dBm 44 20MHz 000C04-005
c4:0a:cb:5c:82:80 -73 dBm 44 20MHz 000B1A3
c4:0a:cb:5c:7d:10 -74 dBm 44 20MHz 000B4A3

84:b2:61:d1:37:50 -53 dBm 48 20MHz 000C04-016
84:b2:61:c7:9a:e0 -59 dBm 48 20MHz 000C04-009
84:b2:61:cf:89:e0 -69 dBm 48 20MHz 000C04-022
d4:a0:2a:d0:6a:20 -72 dBm 48 20MHz 000C3A3
88:1d:fc:26:22:c0 -74 dBm 48 20MHz 000GA16

c4:0a:cb:5c:32:70 -76 dBm 52 20MHz 000W2A3

b0:aa:77:7b:b2:b0 -71 dBm 60 20MHz 000CA12

84:b2:61:ce:2c:90 -61 dBm 64 20MHz 000C04-019

84:b2:61:c8:21:c0 -42 dBm 116 20MHz 000C04-013
84:b2:61:d1:36:c0 -43 dBm 116 20MHz 000C04-011
84:b2:61:c7:08:20 -63 dBm 116 20MHz 000C04-018
2c:33:11:1a:41:60 -65 dBm 116 20MHz 000C04-008

88:1d:fc:48:0b:30 -76 dBm 140 20MHz 000GA22

Highlighted

Hi Guys,

 

Thanks a lot for the response. it has been very helpful. As I mentioned previously, the output sent was when the environment was very quiet and now that everyone is back to work (after the Xmas break) we are seeing 35 -40 users on some of the APs. I will turn off some of the radios as suggested, just worried that the APs wont be able to cope with more users (50-55 users or more) by the time we turn the radios off.

 

Another question, we are seeing some signals from APs' above the floor at  -79 dBm,  -80 dBm on the same channel. Will this contribute to the channel attenuation and still cause Co-channel interference(CCI) to increase. I've always thought that APs with strong signals (-20dBm to -77dBm) will cause significant CCI  and anything else will be less significant.

 

If this can be clarified for me, it will be greatly appreciated.

Highlighted

If they only browse some websites, you should be fine with 50-80 users, without them noticing. This changes once latency sensitive applications come into play though.

To your second question, if I understand it correctly, then to a certain degree yes.
Highlighted

I agree with patoberli.

Cisco actually claims to have at least 200 associations per Radio (total 400 for a dual band AP). With normal data needs , I have seen around 60 clients working with no complaints in our environment.

 

Regarding the second question , I usually make sure that not more than 1 AP are being heard by any AP on the same channel with better than -80 dBm  strength. 

 

Cheers,

Manish

Highlighted

Thanks again for the responses. 

 

so how many users will you say the 3700 or probably 3800 APs can handle for video/voice users using Skype or Lync??? 

 

its going be challenging not seeing not seeing more APs at -79dBm.

 

I will probably be looking at replacing the APs with  patch antenna i reckon (AIR-ANT2566D4M-R) in the office area to minimise the spread all around the office.

Highlighted

My experience with the 3700 APs says , not more than 30 clients using Voice on a single AP. With 3800 , the number may change given that it has MU-MIMO . But still I would like to stick to 30. Going beyond that always looked like a risk to me.

 

Cheers,

Manish

Highlighted

Now we're talking real time applications. Those are very latency sensitive. I also suggest to have no more than 30 simultaneous calls per 5 Ghz radio.
What you can do, if it's mixed traffic, use the controller feature AVC and prioritize Skype and Lync with gold, while the default should be set to bronze. That way you should get good results.