Controllerless Networks

Hi everyone !

Please find an interesting issue that I'm currently facing at customer side. Thank you in advance for your support :)

Context: Customer wants to associate simultaneously on same SSID at least 20-50 devices at the exact same moment (in the future : 5000 in total that would be shifted on a period of time on different IAPs in order to avoid too much simultaneaous connections).

Setup: For now it is really simple since we are still in pilot phase (tried to make it as simple as possible):

• One IAP-325 on last firmware 6.5.3.
• 25 clients (Android mostly) only2,4GHz capable.
• One SSID with WPA2-PSK that will open access to a private network (on native vlan 1). No restrictions (full open). No protection or detection features.
• Each devices have a static IP address in same subnet, just like the IAPs themselves (no DHCP in the network).
• One Access Switch is connecting the IAP and one server, nothing more. No uplink to Internet or different network (fully contain).
• Purpose is for each device to associate to SSID in order to communicate with the server (just the time to DL a 2Ko file and switch off Wifi adapter). 

 Issue:

• After a reboot on the IAP, no clients (not even one at a time) will associate to SSID even though PSK is correct. After rebooting few times more, all good. It is critical to have 100% success since IAP is supposed to be moved /rebooted regularly (mobile kit).
• When working, association to SSID takes long (10-15 secs) IF 25 clients simultaneously try to associate. This is less critical though.

Based on few other topics (not exactly same but similar), I tried to enable "Drop broadcast and multicast" or enable "convert broadcast ARP to unicast". No success. Moreover issue is reproductible on three different AP-325.

To me it sounds like a wireless medium-related issue :/ But could be that a "magic button" isn't enabled.

Thank you guys for your consideration.

SDelay

20 to 50 2.4ghz devices is a heavy lift.  On the SSID in Advanced you should enable "Broadcast Filter ARP".  You should also take a look at the RF utilization on the front page to see the RF utilization on the 2.4ghz band for that AP.  

Hi Cjoseph,

Thank you for your reply.

After opening a TAC ticket, it happened that changing in RF settings "Min transmit power"/"Max transmit power" from 3dBm/max to 12dBm/21dBm solved the association issue. Now issue is different and switched to the second issue: latency.

As you said Cjoseph, you are certainly right that it is heavy lift for 2,4Ghz. I discovered that customer's devices (cheap Android tablets) are programmed to get idle after 25 seconds if no successful Wifi association is made. Resulting with many tablets not succesfully connected sometimes. Does 25sec sound to you an appropriate time frame to simultaneously connect 25 devices Cjoseph ?

I'm thinking to suggest customer to use 3 IAPs in order to fully make use of all 2,4Ghz channels and increase assocation latency, would it be a good idea ?

Moreover, I guess cheap chipset in those tablets might affect the latency aren't they (1SS, no MU-MIMO) ?

Thanks !

SDelay

What kind of android tablets are these?  You might also want to remove some of the lower rates in the advanced portion of the SSID profile.

http://community.arubanetworks.com/t5/Controller-Based-WLANs/Why-do-I-need-to-disable-lower-data-rates-on-802-11g-band/ta-p/174978

Android tablets coming from China, really basic/cheap ones (non public brand). Not sure of the purpose to disable the lower rates here. Would it make available more airtime ? Note that clients are actually just quickly connecting, then download a 2ko file then disconencting (should be few seconds), but all of this simultaneously.

Sdelay

It would make available more airtime, but I don't know to what extent.