CAC Bandwidth for iLBC

I am trying to find the amount of bandwidth that CUCM uses for CAC calculations for iLBC. I have been searching and can not find an answer so I decided I would test on my own.

 

Based on my calculation I figured it would be 32K

I set up a location with a max BW to another location of 32, started performance monitor under RTMT and placed a call. The call succeeded and according to RTMT 29K was used. I thne began lowering my location max BW to 31, 30 and 29 all 3 calls succeeded. I then lowered it to 28 and the call failed with "not enough bandwidth". So I increased back up to 29 but the call still failed, raised it to 30 and still failed, raised it to 31 and the call succeeded. Each time I increased or decreased the BW I monitored the available BW in RTMT and made sure it reflected the change before I attempted a call.

It seems that iLBC uses something between 29 and 31 depending if you are increasing or decreasing BW.

Does anyone know the Cisco official number?

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