flexible radio assignment

[Moudar]

Hi,

I have a classroom with about 35 devices (Ipads and laptops connecting to 5GHz), when all are connected and students are doing what they have to do, the channel utilization is reaching 80 and 90%. So my idea was to use FRA to share the load on 2 5GHZ radios. AP is 2802 and WLC 5520 running 8.10.181.3

When i manually changed the 2.4 radio to 5GHz everything was fine until the next class that the students had!

I was sitting and watching the AP on the WLC GUI (Access Point View)

The problem I had was that many devices jumped all the time between the two 5GHz radios the students had a very bad experience when that was happening. (The devices were settled, no one was moving around) the AP is placed in the middle of the classroom ceiling.

What is Throughput in the picture above? When all were connected Throughput was about 3 Mb, up and down 

[marce1000]

 - According to https://www.cisco.com/c/en/us/support/docs/wireless/wireless-lan-controller-software/200046-tac-recommended-aireos.html . consider using https://software.cisco.com/download/home/286284738/type/280926587/release/8.10.185.0  (there are a number of bugfixes ,                 check if that can help , 

 M.

[Moudar]

isa there any specific bug that is about FRA?!

[marce1000]

                                       >....is  there any specific bug that is about FRA?!
     https://bst.cloudapps.cisco.com/bugsearch?pf=prdNm&kw=flexible%20radio%20assignment&bt=custV&sb=anfr

     Now that list is indeed a bit 'generic'  (indeed) , yet my initial advice remains important because we are 'entering an age' where aireos is getting older because of the new 9800 controller based platform(s). In that context for aireos based controller(s) it becomes more and more advisable (good practice) to go to the latest advisory release (that they can still run).

 M.

[Flavio Miranda]

Hi

  My experience with FRA was never good. The behavior you faced is not acceptable of course but even when you dont face a problem like this, I dont like the solution.  If I were you I would put another Access Point in the room. Just keep them in different channel and you will be good. 

[Rich R]

Agreed with Flavio - roaming between radios is client behaviour so there's not much you can do to control it.  On laptops, depending on what the network driver is, you may be able to set the Roaming Aggresiveness (Intel supports that on Windows) but I don't think there's anything you can set on iPads.  If you make sure the radios are at different power levels that might help some clients stick to the stronger radio but would defeat the purpose of enabling both on 5GHz so you may just need another AP.

To improve channel utilisation reduce the number of SSIDs if you have many and increase your minimum data rate to 24Mbps.

[Moudar]

I have only 2 SSIDs which can't be reduced (corporate and guest).

If the AP is connected to 1G switch port, the throughput according to WLC is 3MB and utilisation  is 60% what does that mean? If i want to compare the throughput to the port speed is that something that we can?!

Why should throughput be improved with increased minimum data rate?

5GHz Data rates in my WLC:

[eglinsky2012]

I've also found that Apple devices are very jumpy when there are multiple radios present. Happens especially in res halls where we have an AP in every bedroom and lots of signal overlap.

I'm surprised 35 devices is overwhelming a 5 GHz radio on a 2800 at 40 MHz. What are they being used for? Streaming video? I'd be interested in what others think about using an 80 MHz channel and enabling MIMO/MU-MIMO if it's not already. (There are checkboxes in different sections of the WLAN advanced settings for "11ac MU-MIMO" and "802.11ax BSS Configuration")

The problem with the XOR radios on 2800s is they are very weak in Tx power. Notice yours is at 2 dBm compared to the dedicated radio at 18 dBm. So, those devices that are roaming between the radios constantly could be on the fringe of the XOR radio's coverage area, and even a person walking by could cause the signal to drop enough to roam. I've heard the 9100 series APs are a little better about this, but still I've been disabling dual 5 GHz mode on the 9130 and 9136 APs we have and just letting them operate in single 8x8 mode instead of dual 4x4 mode to prevent issues like this. The dual 5 GHz mode is better for very high-density, low-obstacle areas like cafeterias and lecture halls, but not normal classroom/office areas IMO.

[Moudar]

Can't use 80MHz because then i will have only 4 5GHz channels (Europe 36-140,  5GHz) which will generate co-channel interference!

I could do that on this specific AP, but we have already about 300MB in speed. Should doubling the channel width do any better?

 

[Leo Laohoo]

AP is a 2800. 

My recommendation is to replace the AP with a different model.  Particularly, do not use 2800/3800/4800/1560.

[Moudar]

Because we have many APs of these models you mentioned. 

Do you mean do not use 2800/3800/4800/1560 particularly with FRA or do you mean do not use these at all!?

[Leo Laohoo]

---

@Moudar wrote:

Do you mean do not use 2800/3800/4800/1560 particularly with FRA or do you mean do not use these at all!?

---

I mean, "do not use 2800/3800/4800/1560".  Ever.  

Every 2800/3800/4800/1560 have a design defect in the shape of the MARVAL WiFi chipset used.  Bottom line is, the chipset would crash and traffic, randomly, gets dropped.  A list of the Bug IDs (there is a long list) can be found HERE. 

[Moudar]

What about Catalyst 9120 APs? Because we have been told that these are the substitute of 2800.

Do 9120 have also many bugs as the Aireonet APs?

What do you advice for substitute of 2700 serie APs (school environment) should it be 9120 or  the 6e new APs 916x?

[Leo Laohoo]

---

@Moudar wrote:

What about Catalyst 9120 APs? Because we have been told that these are the substitute of 2800.

---

Any AP model except 2800/3800/4800/1560.  91xx, for the time being, is immune to this issue.

---

@Moudar wrote:

What do you advice for substitute of 2700 serie APs (school environment) should it be 9120 or  the 6e new APs 916x?

---

If cash is not a problem, 9136.

If cash is going to be an issue, then why throw good money for a "6e" when no one has come up with an affordable "6e" wireless client.  
  

[Rich R]

I would not bother with 80MHz channels.
Increasing minimum data rates improves airtime efficiency which reduces overall channel utilisation.  So if channel utilisation is high then improving it could improve throughput.
Explanation at https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/8-6/b_Cisco_Wireless_LAN_Controller_Configuration_Best_Practices.html#concept_C84096B4070D4377BAA73AB7B4ED05C9 and various other places on the internet.  Most of those articles focus on disabling the 11b data rates but the same principle applies to the higher data rates too.  In https://www.cisco.com/c/dam/en/us/td/docs/wireless/controller/technotes/8-6/Enterprise_Best_Practices_for_iOS_devices_and_Mac_computers_on_Cisco_Wireless_LAN.pdf Cisco actually recommend 12 Mbps but we've actually found 24Mbps works best in our offices and other high(ish) density environments.  Remember higher data rates means smaller cells so make sure you still have adequate coverage.

9120 generally don't have the same issues that Leo is referring to on the 2800's because those problems are mostly unique to the older Wave 2 hardware.

Regarding 9120 or 916x - that's a choice you'll need to make based on cost and requirements.
As 916x is newer you'll get more life out of them and you get 6E support, environmental sensors and a few other new features so all other things being equal, if you can afford them then why not?