why do we need 20% overlap for voice deployment and how to verify the overlap percentage in heat map

[vinodjad1234]

Hi Experts, 

As per cisco recommendation for voice deployment, we need to have 20% cell overlap. I was going site survey documents however I was not able to get the answer for below questions : 

1) Why cell overlap should be 20% in voice deployment , why not 30% or 10% ?  

2) Once we get site survey report with heat map , how to verify the cell overlap percentage ? 

It would be really great if someone could share details about this.

[ali aqrabawi]

i'm not site survey expert but i will share my thoughts :

1) Why cell overlap should be 20% in voice deployment , why not 30% or 10% ?  

30% could be considered very high which may resulting in interference with adjacent neighbor  channels ,,   

2) Once we get site survey report with heat map , how to verify the cell overlap percentage ? 

this is smth i would like to know , but i would say that if i get -67 at the AP edge cells and farther the client will find an AP with RSSI > -67 , then i would say this is a 20% channel overlapping or so .

[mohanak]

The recommended AP cell overlap for VoWLAN deployments at 2.4GHz, is 20 percent. The purpose of the 20 percent overlap is to ensure that a VoWLAN handset can detect and connect to alternative APs, when it is close to the cell boundary. This should allow a VoWLAN client to change AP associations with a minimum of interruption to a call, by minimizing the amount of data rate shifting and retransmission at a cell boundary for a given VoWLAN client.

Refer link : https://learningnetwork.cisco.com/thread/77284