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New Member

7920 re-registers with CME intermittently

Hi ,

We have an issue with a customer running VoWLAN. The solution is deployed in a large warehouse facility with roughly 12 AP's covering a 60000ft facility. The voice quality will be fine for about 30 mins and the will start degrading to the point that the phone de-registers from the CME. About 2-3 mins later it returns to normal. The AP's in the warehouse are using 2.2dbi rubber duck antennae and are spaced roughly 30meters apart in a 2 , 1 configration across the floor. Non-overlapping channels have been used and the power level of 3 has been selected on the WLC. The strange things is that if I have a PC and a laptop configured and associated to the same AP, and I run a ping to both of these devices, the laptop responds 100% but the phone looses 2 - 3 packets intermittently. WCS was recently installed and is revealing de-auth attacks. Not sure where these are coming from, and if these would cause this type of intermittent disconnect and problems on the WLAN. see attached doc.

any advice would be appreciated.


Cisco Employee

Re: 7920 re-registers with CME intermittently

When using the 7920 on the controller, will need to ensure that the 802.1p tag for the platinum qos profile is set to 7.

The 7920 will enter sleep every other 2 seconds, so when in idle, could be some delay in getting ping response.

If on call, will always be awake.

If getting poor voice quality, ensure you have overlapping coverage of the highest rate enabled for the 802.11b network. Sounds like there is a possibility for multipath here as well sine it's a warehouse.

May want to try enabling only lower data rates (i.e. 2mbps).

The 7920 will use the highest rate enabled when on call and the lowest basic rate when in idle. Will not downshift rates for retransmissions.

New Member

Re: 7920 re-registers with CME intermittently


Thank you for your response. By increasing the data rate to a lower rate like 2mbps would it not create very large coverage cells with too much overlap.

I didnt quite understand what you meant around the platinum QoS profile. could you please explain again.

Thanks again


Cisco Employee

Re: 7920 re-registers with CME intermittently

Yes 2 mbps cell would be larger than higher data rate cell.

For the QoS profile, there is an aging feature in 4.0 version, where packets could get aged out within a short period (less than 2 seconds). Due to this, will need to change the platinum qos profile to 802.1p tag of 7 vs 6. Under controller section will see qos profile section. Will want to make that config change if using 7920s.

New Member

Re: 7920 re-registers with CME intermittently

hi ,

Thanks for the explanation. I uploaded a screenshot of some events we are getting on the WCS. It relates to Deauths, do you think this could result in excessive packet loss ?

I am going to try your suggestion on the Qos profile and let you know how it goes.

Thanks !