Wireless Access

I started running some RF reports and noticed very high average channel busy on the 2.4GHz band.   I'm seeing as high as 75% average channel busy on some APs, but it's mostly between 40% - 60% average channel busy.  Originally, I thought it was due to interference from non-wifi devices, but I've found that's not the case.  I did some spectrum analysis tests and determined the interference is coming from our own campus APs.  In my test, I disabled all APs on the floors above and below one floor that was reporting very high channel busy.  Before I turned off the APs, channel busy was around 75%.  After disabling the other APs in this building, channel busy dropped 40%.

 

APs are not on top of eachother from floor-to-floor. They're staggered.

APs are between 25 - 50ft apart.  Roughly 1 AP per 2500 sq ft.

 

Are there any configuration changes I should consider making?

Hi,

Please do some screenshots/or cli outputs of your ap-group profile/ssid profile/radio profile/arm profile (In order for us to understand better what might do this)

 

Some commands that might give us/you some good info:

(Aruba3200) #show ap arm history ap-name "AP NAME"

(Aruba3200) #show ap debug radio-stats ap-name "AP NAME" radio x advanced | include Busy

 

some questions:

• What channels are u using?
• are u using 40mhz in 2.4ghz?
• what is the max EIRP of each AP.
• is ARM enabled?
• what is your AOS version | what is your AP type | ant type?

Also read the following post:

http://community.arubanetworks.com/t5/ArubaOS-and-Mobility-Controllers/channel-busy-in-Access-Point/m-p/44526

 

have a lovely weekend.

 

Me

This AP had a channel busy of 40% for the last week, but is one of the only on the floor that had channel change history:

 

Interface :wifi1
ARM History
-----------
Time of Change       Old Channel  New Channel  Old Power  New Power  Reason
--------------       -----------  -----------  ---------  ---------  ------
2013-02-17 01:08:26  1            1            12         9          P-
2013-02-17 01:02:45  1            1            9          12         P+
2013-02-17 00:55:24  11           1            9          9          I
2013-02-17 00:45:15  11           11           12         9          P-
2013-02-17 00:38:30  11           11           9          12         P+
2013-02-17 00:32:30  11           11           12         9          P-
2013-02-17 00:05:42  11           11           9          12         P+
2013-02-16 23:59:14  11           11           15         9          P-
2013-02-16 23:55:09  11           11           21         15         P-
2013-02-16 23:35:17  11           11           24         21         P-
2013-02-16 23:23:34  11           11           21         24         P+
2013-02-16 23:11:02  11           11           24         21         P-
2013-02-16 22:59:20  11           11           21         24         P+
2013-02-16 22:51:19  11           11           18         21         P+
2013-02-16 22:43:49  11           11           15         18         P+
2013-02-16 22:33:33  11           11           12         15         P+
2013-02-16 22:14:42  11           11           9          12         P+
2013-02-16 22:06:59  11           11           15         9          P-
2013-02-16 22:01:54  11           11           12         15         P+
2013-02-16 21:37:36  11           11           15         12         P-
2013-02-16 21:31:02  11           11           12         15         P+
2013-02-16 21:12:43  11           11           15         12         P-
2013-02-16 20:49:31  11           11           12         15         P+
2013-02-16 20:42:52  11           11           9          12         P+
2013-02-16 20:38:20  11           11           15         9          P-
2013-02-16 20:32:45  11           11           18         15         P-
2013-02-16 20:20:54  11           11           15         18         P+
2013-02-16 20:13:14  11           11           21         15         P-
2013-02-16 20:00:59  11           11           18         21         P+
2013-02-16 19:55:14  11           11           21         18         P-
2013-02-16 19:51:10  11           11           18         21         P+
2013-02-16 19:44:02  11           11           15         18         P+

&

Channel Busy 1s                  54
Channel Busy 4s                  57
Channel Busy 64s                 55
Ch Busy perct @ beacon intvl     62 53 51 55 34 61 53 52 64 60 60 62 61 64 34 64 63 61 65 57 65 63 64 37 62 63 61 59 59 67


What channels are u using?
1,6,11

Are u using 40mhz in 2.4ghz?
No.

What is the max EIRP of each AP.
9 min
127 max

Is ARM enabled?
Yes.

What is your AOS version | what is your AP type | ant type?
6.1.3.4
AP105
Internal

try to low your max eirp level to 15.. (from 127)

tell me if there is any improvement.

(give it at least 5-7 min to run with the new EIRP values while the ARM is enabled)

and print out the same output commands.

 

1- If your client support it turn on 802.11d/802.11h It will make clients and APS negociate power level which reduce interference...

It is recommended to turn it on if your clients support it...  you can turn it on, on rf managment, under 802.11g radio  for 2.4ghz and 802.11a for 5ghz.

2-Turn on Band steering if you dont have it(if you got dual band APS) that will move the capable 5ghz Clients to 5ghz channel which will free more the 2.4ghz channel.   You have to turn it on, on each vap(virtual AP)

 

Note: Optionally, You can try turning mode aware ARM in ARM profile it will dynamically change radios into AM mode if it determines that there is already suffiecent coverage...

Good advise from NightShade1  :smileyhappy:

• Just be Aware! - that mode aware will disable AP units as ACCESSPOINTS and will make some units as AIRMONITORS automatically

(it will do it only If the coverage of current deployment is good enough with less AP on the same area)

---

@kdisc98 wrote:

try to low your max eirp level to 15.. (from 127)

tell me if there is any improvement.

(give it at least 5-7 min to run with the new EIRP values while the ARM is enabled)

and print out the same output commands.

 

---

AP1 - Before & After

Channel Busy 1s                  39
Channel Busy 4s                  36
Channel Busy 64s                 32
@CH Busy perct @ beacon intvl     37 34 39 36 37 41 42 46 45 6 44 40 43 42 41 38 37 6 38 36 37 38 42 39 46 43 43 16 39 36

Channel Busy 1s                  36
Channel Busy 4s                  38
Channel Busy 64s                 37
@CH Busy perct @ beacon intvl     34 32 32 31 71 33 34 30 34 35 36 42 45 35 39 34 34 33 34 36 32 32 35 84 31 34 36 36 32 33

AP2 - Before & After

Channel Busy 1s                  88
Channel Busy 4s                  82
Channel Busy 64s                 82
@CH Busy perct @ beacon intvl     83 88 86 87 87 88 97 88 87 86 85 88 87 94 88 88 86 90 87 91 85 84 83 86 86 89 90 88 87 77

Channel Busy 1s                  86
Channel Busy 4s                  75
Channel Busy 64s                 79
@CH Busy perct @ beacon intvl     85 86 83 94 90 86 85 84 89 82 82 61 78 76 70 75 73 73 72 73 70 88 72 68 66 70 72 76 71 69

 

I'm a little wary about turning on 802.11d/h without doing some more research.  The GUI mouse-over text isn't descriptive enough.

 

I've thought about enabling mode aware, but I am also a little skiddish about this feature.

Do you have Band steering on?

you can turn that without any fear.....if you dont have please turn it on now.

 

If you turn on 802.11d/802.11h if client does not support it, it might have problems connecting.... i dont think you will have issue if your laptops tablets are not that old.... and well if they dont have super old drivers...

I have enable it succesfully on some clients... but i also tell clients that if they  find some device that cannot connect update the driver.  

 

About the mode arm aware it will just turn APs in this case the band of that ap in air monitor...  if he see he has too much coverage...

 

What are your concers about these features?

 

---

@thecompnerd wrote:

---

@kdisc98 wrote:

try to low your max eirp level to 15.. (from 127)

tell me if there is any improvement.

(give it at least 5-7 min to run with the new EIRP values while the ARM is enabled)

and print out the same output commands.

 

---

AP1 - Before & After

Channel Busy 1s                  39
Channel Busy 4s                  36
Channel Busy 64s                 32
@CH Busy perct @ beacon intvl     37 34 39 36 37 41 42 46 45 6 44 40 43 42 41 38 37 6 38 36 37 38 42 39 46 43 43 16 39 36

Channel Busy 1s                  36
Channel Busy 4s                  38
Channel Busy 64s                 37
@CH Busy perct @ beacon intvl     34 32 32 31 71 33 34 30 34 35 36 42 45 35 39 34 34 33 34 36 32 32 35 84 31 34 36 36 32 33

AP2 - Before & After

Channel Busy 1s                  88
Channel Busy 4s                  82
Channel Busy 64s                 82
@CH Busy perct @ beacon intvl     83 88 86 87 87 88 97 88 87 86 85 88 87 94 88 88 86 90 87 91 85 84 83 86 86 89 90 88 87 77

Channel Busy 1s                  86
Channel Busy 4s                  75
Channel Busy 64s                 79
@CH Busy perct @ beacon intvl     85 86 83 94 90 86 85 84 89 82 82 61 78 76 70 75 73 73 72 73 70 88 72 68 66 70 72 76 71 69

 

I'm a little wary about turning on 802.11d/h without doing some more research.  The GUI mouse-over text isn't descriptive enough.

 

I've thought about enabling mode aware, but I am also a little skiddish about this feature.

---

Type show ap monitor ap-list  ap-name <name of AP> and it will tell you how many access points that AP can hear.  You don't want that access point to see more than two APs on the same channel as itself, more than 20 RSSI.

 

Yes, we have band steering enables. 5GHz is preferred.

I get nervous about enabling a feature that could keep devices from connecting, like 802.11d/h. I would say to some extent I don't trust that mode aware will be smart enough to work as advertised. I may have to enable it over a weekend and see what happens.

Our oldest laptops should only be 3 years old. The majority of our laptops are imaged with an old driver. I believes it's a few years old. I'd like to make a push to update drivers but that's another group's responsibility. I can only suggest it.

and how do you see on the monitoring?

what porcentage of the population is connected to 2.4ghz?

guess those are just 2.4ghz capable...

 

Try minimizing it to no more than 3  Best is 2 if you can

new SSID will generate additional beacon and probe traffic

And Yes this create problems...

 

Why you got soo many SSIDS

 

I uploaded for you a study of SSIDs... you will notice on it that with more SSID it affect the throughput, there is more managment traffic...

 

Also do you see any other impact on 2.4ghz ? do you see many ping drops? or you notice that 2.4ghz band its slow? or do you at all see that your wifi performance is poor? or its just that you are looking that on 2.4ghz there is a lot of utilization?

Let me add that at the times that I performed my tests, there weren't many devices on wifi. Most APs were operating at around 9 eirp. So I'm not sure how much .11d/h would help.

I do have have about 4-5 SSIDs on all the APs. I wonder if that creates problems.

For each SSID we have to transmitt a beacon and we send these at the lowest configured rate by default.

So four / five SSID's is 4/5 beacons at 1mbs every 100ms.

+ you then have background traffic and again have to transmitt mcast/bcast at the lowest configured rate (by default - lots of config options available)

 

I personally would get a Wi-Fi packet capture to see what is being transmitted in the Air, it might be as simple as increasing the lowest rate to 6mbs or something like enabling broadcast-filter.

 

 

 

Giles was spot on.  After removing 802.11b data rates, channel utilization is now on average below 20% utlization for all APs.  HUGE improvement!

This outlines the issue we are seeing on campus. Just curious if anyone knows off the top of their head if the wired ports on a 93H will still function if the ap is in AM mode?

Thanks for that doc. I'll start reading it.

I've experienced poor performance when my computer has roamed from 5ghz to 2.4ghz. The way I know I've roamed to 2.4 is that if I'm CLI'd into a switch or controller, there's a noticeable delay when typing in commands. I haven't tested packet loss.

Cjoseph, I'll try that command and see what I get.

One more thing about performance is that colleagues with iPads will complain that they can't connect to wifi today when it was working fine yesterday. Connecting to the network on these devices seems to take longer than it should.

If there is no non-wifi interference, check what I told you before about how many access points connect can be seen by that AP on the same channel over 20 RSSI.  If anyone is on an access point that can be seen by others, when that user Runs something like a speed test, the channel utilization will go up for everyone on the same channel as those access points, because they are in the same collision domain.

 

Quite a few times, coverage from access points travel further vertically than horizontally, so if you put access points right above each other instead of staggering them, you could end up with 3 above each other on the same channel.  Since channel bandwidth is shared, more clients are pulled into the same collison domain and they cannot pass traffic.

 

Also make sure that you are dropping broadcast and multicast at the Virtual AP level to cut down the useless traffic that is being transmitted.

 

Your problem could be a combination of things that everyone mentioned, so you need to check them all to make sure they do not degrade your traffic.

 

 

cjoseph,

 

When I run that command, I see 15 BSSIDs on the same channel with with a current or average RSSI greather than 20.  Average RSSI for those BSSIDs is around 27.

 

I tracked the BSSIDs down to 3 separate APs:

 

1 - adjacent to AP on same floor

1 - above floor, offset about 10 ft

1 - 2 floors below, offset about 50ft

 

I'm not really sure where to go from here.

 

Take a look at one of those other APs and run the command.  If you see the same thing, that AP,  can be turned into an Air monitor, because you have enough coverage in that area.  Create a group that has radios configured as Air Monitors and put that AP in that group.

 

Beisdes what Collin and i telling you

 

I would like to know if your enviroment is a high density envirtoment

 

If it is you should consider

 

1-Turn on Airtime fairness if you havent

2-Take a look on how many users are connnected per band on one AP( let say if you using internal applications and you got like 50 users on one band you surely willl have issues in that AP)

3-If its possible use VLan poolin with small vlans of /24, try not passing of 10 vlan pools mapped to 1 SSID

4-Make sure you please get rid of that many SSIds,  Bealive you will be able to work with 2 or 3 SSIDs if you use 802.1x and derived roles... if you already using 802.1x and not using derived roles consider using it so you can get rid of that many SSIDs.

5-Consider doing Link aggregation between the controller and the Switch you are plugging it, this will help you to have fail over and also if you got HIGH traffic to evade bottle necks

6-Be sure you are connecting ALL the APS to ports of 1000 and also that they syncronized on speed of 1000( you can see that by cli and well you can also see that by lookin at the ap, if the enet power led is not green, and is like orange, then its connected at 100 and you will have a bottle neck there.

7-Turn on like Collin told you filter broadcast and multicast

8-Block Chatty protocols if you can, like bonjour, on the wireless ports.

 

 

This is asumming you got all in the same site and you dont have multisites, which then ill need to know to give more recommendations

 

Cheers

Carlos

cjoseph,

 

My only concern about turning an AP into airm monitor mode is that I'll lose the 5GHz radio as well, right?  An AP can't be in AM mode for one band and serve clients in the other band, right?

 

---

@NightShade1 wrote:

Beisdes what Collin and i telling you

 

I would like to know if your enviroment is a high density envirtoment

 

If it is you should consider

 

1-Turn on Airtime fairness if you havent

2-Take a look on how many users are connnected per band on one AP( let say if you using internal applications and you got like 50 users on one band you surely willl have issues in that AP)

3-If its possible use VLan poolin with small vlans of /24, try not passing of 10 vlan pools mapped to 1 SSID

4-Make sure you please get rid of that many SSIds,  Bealive you will be able to work with 2 or 3 SSIDs if you use 802.1x and derived roles... if you already using 802.1x and not using derived roles consider using it so you can get rid of that many SSIDs.

5-Consider doing Link aggregation between the controller and the Switch you are plugging it, this will help you to have fail over and also if you got HIGH traffic to evade bottle necks

6-Be sure you are connecting ALL the APS to ports of 1000 and also that they syncronized on speed of 1000( you can see that by cli and well you can also see that by lookin at the ap, if the enet power led is not green, and is like orange, then its connected at 100 and you will have a bottle neck there.

7-Turn on like Collin told you filter broadcast and multicast

8-Block Chatty protocols if you can, like bonjour, on the wireless ports.

 

 

This is asumming you got all in the same site and you dont have multisites, which then ill need to know to give more recommendations

 

Cheers

Carlos

---

1. Is enabled.  Set to fair access.

2. It's about a 50/50 split.  However, 3/4 of total sessions calculated for a week are on 5GHz.

 

3. I've thought about using VLAN pools, but wasn't sure what the benefit would be. I will definitely consider doing this.

 

4. I ran another test today and disabled 3 SSIDs that are hardly in use.  I noticed a HUGE decrease in utilization on 2.4GHz.  We're working on a ClearPass implementation and I plan to get rid of the 3 extra SSIDs when we go live.

 

5. I don't believe we're saturating this link, but still a good suggestions.

 

7. Filter Bc/Mc is already enabled.

 

I think getting rid of the extra SSIDs is going to be one of the best things we can do to decrease 2.4GHz utilization, as testing has confirmed. I appreciate all of the suggestions you guys have made!

Good to hear its better now :)

 

I have seem many places having 4, 5 even 6 SSIDs... and its terrible..

 

Anyways about the  mode aware  arm feature you can turn it on just on 2.4ghz band if you want...

Go to ap group-->RF managment-->802.11g radio-->Adaptative Radio managment  and you can check the feature.... just on the 2.4ghz...

 

I would say that if you want to be really sure it does not impact your clients you can always test it on weekends :)  and see how it goes,  Remenber it does it automaically, you can do it manually like Collin Suggested.  :)

 

 

ah yeah you never told me how many users you got per AP...

Iill give you some tips

 

Recommended if you just using wireless for  websurfing and light stuff inside the company, for each radio you should not pass more than 30 user, it is recommeded... Yes you can always have more  but remenber that in wireless this is a half duplex and wireless is CSMA...

So dont think that all the laptops are transmitting at the same time... just one its transmitting... Just imaging that big line of devices wainting for their turn?

That being said also remenber that 300Mbps in one band is not really that is more  150 Mbps once overheads are extracted) 

You have to take many things in consideration!

 

 

 

Ah sorry about that.  At the most we may have around 15 users per AP.

You should not have issue for that part then :)

 

There are many things you can do to tune up your wireless :)

 

Anyways let see how it goes without those 3 extra SSIDs :)

Look if you run 

show ap active ip-addr <ap ip address>

Check to make sure:

Channel Frame Retry Rate % is below 30%. If higher then too much

interference.

Channel Noise Floor is above 80. If Noise Floor is lower then too much

non-802.11 interference

 

Now if sems that you got too many APS on the same Channel,   you might be doing overcoverage and you might want to turn som of those raidios in air monitor...