topic high b/g channel utilization in Wireless

high b/g channel utilization

Srin_G — Sun, 04 Jul 2021 05:49:57 GMT

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

Re: high b/g channel utilization

Scott Fella — Mon, 15 Oct 2012 13:19:02 GMT

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.

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Re: high b/g channel utilization

George Stefanick — Mon, 15 Oct 2012 16:42:16 GMT

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
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Re: high b/g channel utilization

Shankar Ramanathan — Mon, 15 Oct 2012 18:56:55 GMT

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 Configuration	Value
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 Rate	Bandwith Utilization
1 Mbps	39.20%
2 Mbps	19.60%
5.5 Mbps	7.13%
6 Mbps	6.53%
9 Mbps	4.36%
11 Mbps	3.56%
12 Mbps	3.27%
18 Mbps	2.18%
24 Mbps	1.63%
36 Mbps	0.82%
48 Mbps	1.09%
54 Mbps	0.73%

Re: high b/g channel utilization

George Stefanick — Mon, 15 Oct 2012 19:05:35 GMT

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.

high b/g channel utilization

Saravanan Lakshmanan — Mon, 15 Oct 2012 19:25:51 GMT

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

George Stefanick — Mon, 15 Oct 2012 19:32:20 GMT

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

high b/g channel utilization

Saravanan Lakshmanan — Mon, 15 Oct 2012 19:37:42 GMT

Thanks!!! George.

high b/g channel utilization

Srin_G — Tue, 16 Oct 2012 01:51:18 GMT

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!

high b/g channel utilization

Scott Fella — Tue, 16 Oct 2012 01:56:43 GMT

You forgot to add the screen shots.

Thanks,

Scott

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

high b/g channel utilization

Srin_G — Tue, 16 Oct 2012 02:59:52 GMT

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.

high b/g channel utilization

Srin_G — Tue, 16 Oct 2012 03:04:45 GMT

sorry mate was in a hurry

high b/g channel utilization

Srin_G — Tue, 16 Oct 2012 03:06:20 GMT

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

Srin_G — Tue, 16 Oct 2012 03:07:30 GMT

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

high b/g channel utilization

Srin_G — Tue, 16 Oct 2012 03:08:26 GMT

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

Re: high b/g channel utilization

daviwatk — Tue, 16 Oct 2012 04:14:06 GMT

Hi Srini,

It's tough to tell you what changes to make without seeing your current run-config so we can see the total RF snapshot of your environment. The spectrum analyzer look mostly like BT, but maybe some DECT phones as well since you mentioned. Several topics above are quite valid regarding channel utilization but be sure to consider the specific requirements of the clients you are servicing before making changes relative to their communication.

I'm not sure what version you were running the last time you used the WLCs RRM features, but this is really probably your best bet, but may require some tweaking. With those 8.5dbi antennas maxed at power level one, you may be overpowering your environment, but I can't say for sure without run-config.

I would usually suggest the WLC's RRM defaults a starting baseline. I'm not sure what version your last RRM experience was with, but this is quite a polished solution. You may need to make various changes, but you can get a better understanding of the current RF based upon the WLC's choices.

For instance, if you set all RRM to Defalut and Auto and after several intervals you find your power levels dropping to 4, 5, and so on, you would immediately know that your manual power assignment is severely impacting the RF with co-channel interference. Given your description, I wouldn't suspect your power levels would stay at levels 1 and 2, but can't say for sure without current run-config.

high b/g channel utilization

Srin_G — Tue, 16 Oct 2012 05:28:43 GMT

The TAC says it is layer 1 inteference as I found from airmagnet spectrum. May be the environment is too hot as well as we use custom power level for all AP's as 1. Now that we have increased AP density i am thinking whether TPC can help to reduce co-channel interference as we can play with only 1,6 and 11. Proper site-survey wasn't done as we followed the standard AP placement template for warehouse.

The AP is wall mounted 8m high from the floor with no tilt of antennas. The aisles are fully stocked and 7m high it looks like a thick wall...so we are just skeptical about the coverage we would received in the middle of the floor especially from 1-3m from the floor.

I think TPC is based upon the readings received from neighbors.In our environment most of the AP's can see each other so TPC will decrease the power of the AP but the client will get bad signal especially in the middle of the floor.

Studying the signal pattern of the antenna we use it helps to have a tilt towards the floor by an angle...is there any formula to calculate the tilt in a indoor environment? To start with we are going to disable 1M and try to find the interference source.

Thanks guys.

Re: high b/g channel utilization

daviwatk — Tue, 16 Oct 2012 15:56:04 GMT

TPC could certianly help out. If you have added even more APs and are still maxing power at one, you are probably pretty hot. TPC will make the "best" choice in regards to power levels. Please also consider the maximum transmit power of your clients. Maxing the AP out to reach your center aisle could have zero effect (and mostly negative) if your clients have a max 50mw transmit power; just as an example. the AP needs to hear your client, so I wouldn't depend on your client having "more bars" as indication of proper performance for that client. The interference appears to be BT due to the FHSS CU sequencing, which is a concern, but the power level assignments could be doing more harm than these.

Without a site survey it's anybody's guess what's best for your environment. Again, a run-config would go a long ways in making suggestions for you.