Could you provide the following in order to allow us to better help you:
1) What firmware version are you running on the WLC?
2) What type of security are you running (WPA2-Enterprise, WPA2-PSK, open, etc.)?
3) Are only Apple devices affected in terms of connectivity?
4) If you are using WPA2-Enterprise, what type of authentication are you using (PEAPv0-MSCHAPv2, EAP-TLS, etc.)?
5) Is this happening on both the 2.4GHz and 5GHz bands?
6) Is there a reason why you disabled 802.11n?
7) Have you ruled out a non-802.11 interferer in the area?
8) Have you upgraded the firmware version of the clients?
As you can see, there are a ton of factors that could be leading to this issue, and more than I've listed. We need more information to provide better help.
answering your questions
1) WLC firmware 220.127.116.11
3) only apple devices
4) auth pre-share, encyption AES
5) only on 2,4GHz, we are not using 5GHz
6) we disabled "n" because of the connectivity problems with apple devices. Besides, is there any known incompatibility between apple and "n" standart?
7) cannot tell you for sure, but the area is not so huge, it an office with several cabinets without any microwave or smth
8) apple devices are with different iOS systems, some of them use last iOS5
I thought there can be smth similar to airprint, when you should enable multicast on WLC...
Thanks for the responses. I would recommend upgrading to 18.104.22.168. I don't see anything in the release notes that would impact your situation, so that's just a general recommendation as it contains fixes for other things. I'm not aware of compatibility issues with 802.11n and Apple devices. We've had all types of Apple devices on our network, running WPA2-PSK/AES and 802.11n.
One thing I did have to do at one point was to uncheck "Enable Aironet IE" under the WLAN Advanced tab. We had a couple of Apple devices that would not connect properly with that enabled.
As for the office, are there other companies' offices around yours? It's possible that they are causing enough interferance with yours to cause the drops. I'd use something like inSSIDer or Netstumbler to see what other 802.11 networks are around you. In particular, see if any are operating on a channel other than 1, 6, or 11. That can really mess things up for your network if they are.
iCloud uses a unicast stream, so no need to enable multicast.