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high b/g channel utilization

Hi guys, having lot of issues after adding 8 extra AP's in our warehouse floor to get more coverage. Out of the existing 32 AP's on the floor 70% of the AP's have more than 80% channel utilization. It is b/g network so we use 1,6,11. We dont use TPC or DCA as we had lot of issues in our warehouse with it before. The transmit power is custom "1". Data rates 1 and 2 are set to mandatory..will disabling it help? I am going with the spectrum analyzer tommorow to see if i can find something. We have VoWLAN (used sparringly though) in the same 2.4Ghz spectrum too will it increase the duty cycles? I have scaled down the QoS from platinum to best-effort but its still the same. Bounced couple of AP's but no luck. I think it is co-channel interference but utilization over 80% and in some AP's it is  even 91% ....quite ridiculous.    

Any suggestions are appreciated!

cheers            

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17 REPLIES 17
Hall of Fame Master

Re: high b/g channel utilization

Well when adding AP's, maybe lowering the TX is one thing to try. I usually disable everything below 11mbps, but that's if your devices don't require those low data rates. You can set 11mbps as mandatory or even go higher than that and set 24mbps as mandatory and 11mbps as supported. You need to walk through and determine your coverage and tweak as needed.

Sent from Cisco Technical Support iPhone App

-Scott
*** Please rate helpful posts ***

Re: high b/g channel utilization

One of the biggest challenges with warehouses is RF shaping. Most warehouses are designed with Omni antennas which are installed to the rafters. From the ground, when looking up you may only see that 1 ap, as your are standing between racks.

However, get on a lift. Once up at rafter level take a 360 degree look. Can you see all the APs and Omni's? If so, guess what ... They also see each other. This is a very large contributor to high utilization.

If this is your case. You may want to survey with more directionals and shape the RF and use less Omnis.

__________________________________________________________________________________________
"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
__________________________________________________________________________________________
‎"I'm in a serious relationship with my Wi-Fi. You could say we have a connection."

"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
___________________________________________________________

high b/g channel utilization

George, we dont use OMNI we had three but disabled them after adding 8 extra AP's (see my screenshot of the floorplan) we use patch 2485!

regards

Cisco Employee

Re: high b/g channel utilization

How many SSID's are in active use? Turning off 1 and 2 MBPS as mandatory data rates would definitely help in lowering channel utilization (if you do not have clients like scanners which might need them)

So for a sample network looking with config below

Network ConfigurationValue
Average Beacon Size (bytes)             140
Beacon Interval  (ms)             100
Number of SSIDs per AP                 5
Number of  Nearby APs                 7

Beacon Bandwidth estimation:

Basic Data RateBandwith Utilization
1 Mbps39.20%
2 Mbps19.60%
5.5 Mbps7.13%
6 Mbps6.53%
9 Mbps4.36%
11 Mbps3.56%
12 Mbps3.27%
18 Mbps2.18%
24 Mbps1.63%
36 Mbps0.82%
48 Mbps1.09%
54 Mbps0.73%

Re: high b/g channel utilization

Actually beacons are set at 102 mill. Not 100. This is a cosmetic issue for a lot of vendors. Actually sniff the beacon.. You will see they come every 102 mill.

This is becuase of the target beacon transmission time (TBTT) uses kilomicroseconds. Due to the powers of 2 this means its 1024 mircoseconds or 102 milliseconds. 

__________________________________________________________________________________________
"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
__________________________________________________________________________________________
‎"I'm in a serious relationship with my Wi-Fi. You could say we have a connection."

"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
___________________________________________________________

high b/g channel utilization

yeah mate we got about 12 ssid's i know its a over-kill.

Cisco Employee

high b/g channel utilization

We have VoWLAN (used sparringly though) in the same 2.4Ghz spectrum too will it increase the duty cycles?

No.

Mitigating channel utilization:

#Enable DTPC. however, it works only with CCXV2 compatible client.

#General>> 802.11b/g/n>> RRM>> General>> Change the channel List to DCA, increase the Monitor intervals of #Channel scan interval and neighbor packet freq.

#Do you use mix of b and g clients. if so that can catalyst channel utilization through cts.

#Are Many WLANs broadcasting with lower datarates enabled on them. If so use only couple of them for airtime fairness.

#AP with channel utilization greater than 70% is unusable.

http://www.cisco.com/web/strategy/docs/education/cisco_wlan_design_guide.pdf

The impact of non Wi-Fi interference is logarithmic in its impact on Wi-Fi network operations. The higher the utilization of the Wi-Fi network, the more destructive non Wi-Fi energy will be. This means that if there is interference present and the network is only slightly utilized (e.g., there is ample duty cycle available within the spectrum), the presence of non Wi-Fi energy may not even be noticeable. There is space for both to share the spectrum. However, if the Wi-Fi network is highly utilized, then even a small amount of non Wi-Fi interference can have a large and noticeable effect.

http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a0080810880.shtml

For RF environments that are clear spaces, like factories where there are access points in a large space without walls, it might be necessary to adjust the Transmit Power Threshold from the default of -65 dBm, to a lower value like -76 dBm. This allows you to lower the co-channel interference (number of BSSID heard from a wireless client in a given moment). The best value is dependant on each site environmental characteristics, so it should be evaluated carefully with a site survey.

high b/g channel utilization

SL you've been on FIRE lately with some good post .. All this extra content is keeping me up late at night.. Keep it up ! +5

__________________________________________________________________________________________
"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
__________________________________________________________________________________________
‎"I'm in a serious relationship with my Wi-Fi. You could say we have a connection."

"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
___________________________________________________________
Cisco Employee

high b/g channel utilization

Thanks!!! George.

high b/g channel utilization

Thanks George, SL, shankar and Scott. Did a spectrum analysing today and can see heavy interference. Cant find the source where it comes through but could guess a location. TAC says disabling the lower data rates wont help as this is a physical layer issue. we are still skeptical about DCA and TPC as it gave us lot of headaches before in warehouse environment. Please go through the screenshots we u guys have a time.

cheers guys!

Hall of Fame Master

high b/g channel utilization

You forgot to add the screen shots.

Thanks,

Scott

Help out other by using the rating system and marking answered questions as "Answered"

-Scott
*** Please rate helpful posts ***

high b/g channel utilization

sorry mate was in a hurry

high b/g channel utilization

This is interfering device type the analyzer came up with...not sure it is our AP or someone's bridge as i cant see the mac-address

high b/g channel utilization

Thanks mate. please see our floor plan this is after we added 8 extra AP's. The three AP's in the middle of the warehouse are OMNI but we have disabled the radio as it caused more interference.The rest of the AP's are patch 8.5dbi.

The spectrum analysis shows some wideband bridge/router or cordless phone causing massive interference but we cant indentify the mac-address.

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