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Wireless phones drop connection when multiples phones on same AP

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.

5 REPLIES
New Member

Re: Wireless phones drop connection when multiples phones on sam

Let me add a couple more details. These are 802.11g phones, and they start dropping around 6-7 phones. They are configured for G.729. I know of the limitation of 7 phone for 802.11B from http://www.cisco.com/en/US/products/hw/phones/ps379/products_implementation_design_guide_chapter09186a00802a0a05.html, but we have more bandwidth here.

Cisco Employee

Re: Wireless phones drop connection when multiples phones on sam

So this isn't the Cisco 7920 then as it's only 802.11b, but you are referencing our 7920 design guide. We don't encourage using G.729 unless the RTP is traversing a WAN. If local, then use G.711 or maybe G.722 if supported. The 7920 will not drop a call even if travelling out of range, but maybe far end may disconnect if no audio is heard.

Also some clients may drop calls if they support CAC / TSPEC and get a rejection message after roaming to another AP or don't get a ADDTS response.

Re: Wireless phones drop connection when multiples phones on sam

Your RF environment is also playing a factor.. How are you stating you have more bandwidth? Are you referencing the number of APs you have serving an area or are you referencing the wired connection to the AP?

New Member

Re: Wireless phones drop connection when multiples phones on sam

The number of APs. There are 8 802.11G APs, and we might only be able to use 6 or 7 802.11G wireless phones before the connections drop.

Cisco Employee

Re: Wireless phones drop connection when multiples phones on sam

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.

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