Primary (K-12) Education

Hello Everyone,
I am running into a problem with a new group of chromebooks we purchased. They are the Dell Chromebook 3100, which uses an Intel Dual Band Wireless AC 9560 wifi card. When we have a class of students using this chromebook model, say 5 or more, access to the internet becomes extremely slow to the point that it is unusable. When looking at the health of the connection to each client, the controller reports it to be bad. When we try a different set of chromebooks like the Dell Chromebook 5190, which uses the Intel Dual Band Wireless AC 7265, we have no problems. Also, with other older model chromebooks, we have no issues. The AP’s I am using are the Aruba 345 with Aruba OS 8.5.0.5 and 7205 mobility controllers.    Is anyone else running into this problem?

What can you tell use about the used channel bandwidth and used channels and what about SNR to the clients? Are they 2.4 or 5Ghz connected?

 

Most likely this is a client driver issue but it can also possible that the AC9560 dont support some channels, but i dont have specs of that interface. Did you update the latest drivers for this adapter?

 

Maybe you could capture some "Association Request" with a 802.11 packet traces?

 

https://ark.intel.com/content/www/us/en/ark/compare.html?productIds=99446,83635

 

https://clients.mikealbano.com/contribute

Hello Marcel   thank you for assisting,

Clients are connected on the 5 Ghz band and SNR ranges from 50 – 58 db.  Client Client bandwidth and radio bandwidth both report as VHT 80MHz and client Health score 0%.   Total channel utilization for 5 Ghz band is 30% and ranges up to 50%.

I don't know much about your network, but if you are running 80mhz channels (E) in a network with density, this should be adjusted to 40mhz channels to avoid cochannel interference.  That will give ALL clients a chance to perform better and in turn make it better for your Chromebooks that might be less tolerant in that atmosphere.

 

EDIT: 50% channel utilization on the 5ghz band is not bad in bursts, but if it is sustained, that is too much, so you should look at  running 40mhz channels AND possibly reducing the transmit power of your access points.

Hi,

 

Collin is fully right, never! do 80mhz (except at home in some situations;)). You will quickly got to much co-channel interference. In education i will advise 40mhz or even lower to 20mhz in very high density enviroments like exam area where are a lot of clients together.

 

But the most likely root cause you will maybe find in this topic.

https://forums.intel.com/s/question/0D50P0000490Y3TSAU/intel-wirelessac-9560-not-working-with-channel-36-and-80mhz-width?language=en_US

 

AC-9560 intel chipset supported channels:

 

 

I would have to chime in here as well - we dropped everything to 20mhz bands due to similar issues.  We have a vibrant BYOD program here and found that we never have connectivity issues with odd clients when set to 20mhz.  We also have a fairly dense deployment of APs so this helps significantly with channel overlap.

 

-Dan

cjoseph

Currently, each classroom has around 25-40 devices with one Aruba 345 in each room. I'll try disabling 80 Mhz support later today. What are your recommendations on the settings I'm currently running below?

 

Adaptive Radio Management (ARM)

 

default-a

Assignment: single-band

Allowed bands for 40MHz channels: a-only

Min Tx EIRP: 12

Max Tx EIRP: 18

Client Match: Enabled

 

default-g

Assignment: single-band

Allowed bands for 40MHz channels: a-only

Min Tx EIRP: 6

Max Tx EIRP: 9

Client Match: Enabled

Try to put your 5GHz radio a little lower, 9 - 15 should be a good starting point. 2.4GHz radio looks fine to me.

 

default-a

Min Tx EIRP: 9 dBm (8mW)

Max Tx EIRP: 15 dBm (31mW)

 

Note: Minus 3dBM half the TX power (18dBM=63mW)

 

Another optimazation, disable the lower basis rates below 24Mbps to optimize roaming and keep airtime clean. This also avoid very old and slow 802.11b devices to connect that could consume all available airtime.

 

Marcel, when it comes to disabling the lower basis rates, would I turn these off for both basic and transmit rates? and would i need to turn on everything from 24 and above for the basic rates? 

FWIW, I would stray away from manipulating data rates unless you have a good understanding of the impact it’ll make. Do you have evidence that management and control frames are consuming a large percentage of in-air bandwidth? If so, go for it. Without the evidence though, you may compound the problem by introducing interoperability issues with your clients.

My two cents.

- Ryan -

---removed dubble post---

I agree it depends on some factors and there is no good or bad. For education are this the recommended values following the "RF and Roaming Optimization for Aruba 802.11ac" design guide, link. (page 11)

 

802.11a/ g: Basic rates: 6,12,24
802.11a/ g transmit rates: 6,12,24,36,48,54

 

Basis rates are for management frames, beacons are always send at the lowest basis rate. Transmit rates are for data frames.

 

Personaly i like to disable 6 and 12 rates aswell, when disable 6 the old legacy 802.11b are not able to connect anymore.

 

Marcel, thank you for the help, after disabling the 80 mhz band the issue with the Dell Chromebook 3100 has been resolved. Also, thank you for the link to the RF and Roaming Optimization for Aruba 802.11ac guide it has been very beneficial.

Thank you for your feedback and good to hear that we have been able to help you.