Wireless phones drop connection when multiples phones on same AP

Question

I'm attempting to find a solution as to why wireless phones drop the calls when there are multiple phones associated with an AP. The BW usage of the phones is a small fraction of the available BW. Call quality is OK with multiple phone associations, and a single phone on an AP does not drop a call.
There doesn't appear to be any pattern associated with the dropped calls. Not every phone drops a call, but this happens frequently.
Thank you.

Answer 1

Are these Cisco APs? If so, can enable QBSS.
For Cisco IOS, enter "dot11 phone". For Airespace is called "AP CAC Limit" in the WLAN config. This will send a Channel Utilization value to the phone for that AP's channel. If 12.3(7)JA or later, this will be CCA based value showing true channel utilization. This is on a 255 scale, where default limit for calls is 105. Can still receive incoming calls though when > 105.
The phone call shouldn't be dropped though even if AP association is lost, unless some device is disconnecting the call due to not receiving any RTP packets (i.e. Cisco CallManager Express). If this is a 7920, go to the 7920 site survey to view the CU value. The last # displayed will be the QBSS / CU value. If this somewhat > 0 (i.e. 30+ or so) without any 802.11 traffic present, then may want to investigate what devices or causing this load on the 802.11 channel. An option could be to move to another channel as well. Ensure non-overlapping channels are used though per 7920 scanning mechanism and to ensure seamless roaming.
If these are 7920s, recommend using 3.01 fw.