Wireless Access

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Contributor I
Posts: 20
Registered: ‎11-10-2016

Channel busy absolute number

I find channel busy report on Aruba AirWave but what does it really refer to..?and what is it 100% absolute number..? does it refer to radio frequency capacity..? how do it being calculate..?

Mohamad Syafiqul Haziq,
System Engineer, Mesiniaga Berhad.
MVP
Posts: 514
Registered: ‎11-04-2011

Re: Channel busy absolute number

As the radio in WLAN can only start transmitting if there is no other signal (can be both other WiFi or non-wifi/interference), the capacity of a channel is dependent on how much of the time a radio can transmit.

 

The channel busy is a percentage (0-100) where 0 means that the channel is free all the time, and 100 means that it is occupied all the time. So it is an indicator of the available capacity on a radio.

 

In most places, the channel busy is also broke down to WiFi and non-WiFi channel busy. The non-wifi indicates that other systems are using the same channel and cause interference. High WiFi channel busy indicates a saturated channel and indicate that you might need to add capacity.

 

If channel busy goes above 30% over longer periods (number is arbitrary.. just an indication), it may be a good moment to see what is happening at that location and see if you can change the location or number of APs. Typically you will see much higher channel busy on 2.4 GHz, and lower on 5 GHz.

 

Check also: https://community.arubanetworks.com/t5/Controller-Based-WLANs/How-do-we-handle-Channel-Busy-on-RF-and-the-factors-that-could/ta-p/178794

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Contributor I
Posts: 20
Registered: ‎11-10-2016

Re: Channel busy absolute number

Thanks for the reply..it really help..

what I'm curious about is, does this channel busy affect the wireless throughput..? or does it have direct impact to the throughput..? or does it represent the wireless bandwidth capacity..?

Mohamad Syafiqul Haziq,
System Engineer, Mesiniaga Berhad.
Contributor I
Posts: 20
Registered: ‎11-10-2016

Re: Channel busy absolute number

Thanks for your response.

 

I am curious over the 30% rule of thumb.

 

And my assumption this had came about by the assumption that we only get about 25%  (or 30% as you said) of the theoritical throughput; for example in a 802.11a network with theoritical limit of 54Mbps the real thruput is only about 25% or about 13 Mbps. 

 

Therefore, if this is true, the 25% (obeserved from the system)  represents the actual or like the max thruput; or the 100%.

 

Cheers

Mohamad Syafiqul Haziq,
System Engineer, Mesiniaga Berhad.
MVP
Posts: 514
Registered: ‎11-04-2011

Re: Channel busy absolute number

That is a bit a dual thing. So wireless throughput will cause channel busy as it occupies the channel. So if the channel busy is yours, it is throughput, if it is by someone else it is taking your capacity... Remember WLAN is a shared medium; you can use the 'airtime' only once.

 

If you have high channel busy it is either your clients pushing lot of data, or others taking your airtime. Also note that if your clients are closer, and have stronger signal, they will get higher data-rates and can push more data in the same airtime. So it is all very dynamic; but basically if you have high channel busy you might not have enough spare capacity to grow and you are hitting the upper boundary of your capacity.

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If you have urgent issues, please contact your Aruba partner or Aruba TAC (click for contact details).
Guru Elite
Posts: 21,267
Registered: ‎03-29-2007

Re: Channel busy absolute number


shiqol wrote:

I find channel busy report on Aruba AirWave but what does it really refer to..?and what is it 100% absolute number..? does it refer to radio frequency capacity..? how do it being calculate..?


Yes, it is radio frequency capacity from the point of view of the access point that is measuring it.  There is no magic number and some of the "capacity" you have control over and some of it, you do not.  Non-RF interference, and RF interference from external access points are two examples of RF utilization you have no control over.  The power of your own access points, the channels you choose for them, whether or not you have broadcasts and mutlicast filtering enabled, whether you choose to remove lower rates, how many SSIDs you are broadcasting, and how many clients you allow on each access points are examples of things you have control over.

 

Typically, you should look at the RF utilization on the radio band of an access point overnight when there are few to no clients on the radios, like at midnight.  The RF utilization should approach 1-4% of the spectrum at that time.  Anything more than 4% and most likely you are creating your own "interference".  If it is above 4% overnight, I would consider:

- Lowering the maximum transmit power on that band by 3db for those radios (I would only go to a minimum of 9)

- Making sure that broadcast filtering is on all of your SSIDs (instant) and Virtual APs (controller-based)

- Making sure you have no more than 4 SSIDs broadcasting on an AP and if you have more, consider how you could possibly remove or consolidate them.

- Consider removing the "lower" rates from your SSIDs to increase the rate at which the access points beacon, which reduces utilization.  It will also encourage clients to roam more quickly to access points that they should be on, instead of sticking to APS further away and dragging down performance.

 

Long story short,  in Airwave I would look at the utilization graph in airwave on the radio of an access point on a week's time interval and plot it against the number of clients.  If the utilization is above 5% overnight, use the methods above to figure out how to reduce the part that you have control over.  After you make the changes, look at the utilization the next night and see if it drops to under 5% to see how much of a difference you made.  In your week graph, see if the rise in utilization correlates to how many clients are associated to that radio.  If it does, determine if too many clients end up on that radio (more than 40) and consider reducing the transmit power on that radio or removing lower rates to encourage clients to move.  24 hours later, look at the weekly graph and see if the number of clients has reduced and if the utilizaton has reduced as well.

 

The utilization for an access point's radio differs based on location and use.  You should look at your utilization a week at a time to baseline if your clients have greater utilization when you see complaints.  If they do, use the methods above to make changes to the things you have control over...

 

http://community.arubanetworks.com/t5/Technology-Blog/Removing-the-Bottleneck-in-Wireless/ba-p/77978



Colin Joseph
Aruba Customer Engineering

Looking for an Answer? Search the Community Knowledge Base Here: Community Knowledge Base

Contributor I
Posts: 20
Registered: ‎11-10-2016

Re: Channel busy absolute number

well..does RF utilization differ for each SSID and each channel..?or does RF utilization refer to overall channel utilization..? 

While saying that, does interference and noise impact the RF utilization..?

Mohamad Syafiqul Haziq,
System Engineer, Mesiniaga Berhad.
Guru Elite
Posts: 21,267
Registered: ‎03-29-2007

Re: Channel busy absolute number

- It affects the whole channel, so it reflects ALL SSIDs, whether they are yours or not.

- Both interference and noise can affect RF utilization, but it varies.



Colin Joseph
Aruba Customer Engineering

Looking for an Answer? Search the Community Knowledge Base Here: Community Knowledge Base

Contributor I
Posts: 20
Registered: ‎11-10-2016

Re: Channel busy absolute number

Thanks for the answer..so may I ask your opinion regarding the attached picture..which variable effect the channel busy the most..?

Mohamad Syafiqul Haziq,
System Engineer, Mesiniaga Berhad.
Guru Elite
Posts: 21,267
Registered: ‎03-29-2007

Re: Channel busy absolute number

Busy is the total of all of the others.  You should have a 24-hour graph that shows what the channel busy is at midnight.  It looks way too high, already, honestly.



Colin Joseph
Aruba Customer Engineering

Looking for an Answer? Search the Community Knowledge Base Here: Community Knowledge Base

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