settings to encourage iPads to switch wifi networks/APs

[tschaps]

We are a school with an iPad program which started this year. About 1,500 iPads and 60 Apple TVs for iPad mirroring throughout the school with 62 MSM430's and MSM466's controlled by two teamed MSM765zls. Up until this past weekend, the iPads and Apple TVs were all on one subnet. Crazy as it sounds, it all has been working quite well and so splitting up the broadcast domain got pushed to the backburner until other tech issues were resolved.

But now we have two iPad/Apple TV subnets with two SSID's on two different VLANs and subnets, each covering about the half the school (let's call them SSID1 and SSID2). As the single VSC setup before it, these networks are not access-controlled VSCs, just WPA2-encrypted on both 5 Ghz and 2.4 Ghz radios, controller providing authentication. In testing, we found that we could not use the same SSID for both zones/subnets, because while the iPads hop quite well between APs during passing time, if they connect to a network with the same SSID as the previous one, they do not attempt to renew their DHCP lease, so they end up with no network connectivity when moving to the other zone. WPA2 network configuration profiles are pushed out from our MDM system, so the students never touch or see the passwords.

Today was the first test day, and it mostly worked quite well, no big problems, but as expected, the 'border' area had a few issues. Specifically, in the library some iPads are hanging on to the SSID2 across the "border" which they were associated to before walking into the library instead of hopping to the new AP on SSID1 in the library, I assume because it is a different SSID. Cycling the wi-fi on the iPad quickly resolves the problem in most cases, but I'm trying to figure out a way to get the iPads to more quickly give up the now weak SSID2 and connect to SSID1 without user intervention and without degrading performance.

The iPads generally connect to the 5 Ghz radio very well, but they have the 2.4 Ghz option they can use. I know that if I increase the multicast Tx rate, it noticeably increases the performance with 50-60 iPads connected, but if I increase it too much, I find I cannot get very far away from the radio before I lose network and mDNS connectivity even though signal strength is still pretty good. This isn't helpful for my need, I need the iPad to want to hop to the stronger radio or else have the radios push the iPad away when their signal strength goes down.

I'm looking for recommendations how to balance all the various settings: multicast Tx, allowed wireless rates, QOS, "Distance between APs", etc. to achieve what we need. I don't think, from my understanding, that moving to an access-controlled setup, wireless mobility settings, or even RADIUS would help this, but I am open to it. I do know from my research that the iOS devices cannot make use of WPA2 opportunistic key caching, though I am not sure that would help here anyway. As I said, the iPads hop between APs amazingly well when the same SSID is present.

Also important to note that Bonjour/MulticastDNS is used heavily for many services, including allowing the iPads to find the Apple TV of the room they're in (Apple TVs are wired but on same subnet as the iPad zone). So maintaining a distinct border between the SSID1 and SSID2 zones is important. We found the best 'border' lines we could to reduce bleed over, but there are a few problem areas as described.

Any help appreciated. Thanks

[Georgeisaac]

Roaming decisions are taken careby clients not by WAPs (DCF).Seamless roaming is not poosible with diffrent SSIDs as per current wireless standards..Wireless standards like 802.11u are coming up which can provide seamless roaming irrespective of SSID..

[tschaps]

I apologize that this response took so long. 

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@Georgeisaac wrote:

Roaming decisions are taken careby clients not by WAPs (DCF)...

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I understand that, but the clients make that decision based on certain factors relative to the quality of the wireless signal, so I am wondering whether I can tweak networks settings to make conditions right to encourage the clients to look for other networks and make the leap sooner, instead of trying to hang on to a wireless network in another zone. 

It seems to me some combinations of all the settings we have access to would affect those client roaming decisions .

thanks

[gguynes]

Checking to see if you have come to a conclusion to your request?  I am facing many of the same questions surrounding apple devices and AppleTVs.

[tschaps]

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@gguynes wrote:

Checking to see if you have come to a conclusion to your request? ...

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Not really, i set up special AP groups for the border AP's which had the VSC used by the iPads only on 5 Ghz and the 5 Ghz radio broadcasting at reduced power. Though the iPads almost always grab a 5 Ghz signal anyway, this setup assured that iPads near the 'borders' would be on 5 ghz and a weaker signal, so as users crossed the border into a different zone of the school, they would lose the signal faster. The iPads are very good at quickly associating to the other network zone SSID's and getting an IP address, so that by the time the student sits down in a classroom, the iPad is ready to go, and it's on the correct subnet for using the Apple TV in that classroom. 

I was hoping for a more elegant solution, but that one worked and continues to work, I assume, but I left that job two months ago, so I am no longer in that particular loop.

Good luck, T