Cisco Cisco IOS Software Release 12.2(8)T

Router(config-if-atm-vc)# vbr-rt peak-rate 

average-rate [burst]

Configure the PVC for the variable-bit-rate real-time 
(voice) traffic. Guidelines for setting the peak rate, 
average rate, and burst size are as follows:

peak rate—If it does not exceed your carrier’s 
allowable rate, set to the line rate (for example, 
1536 kbps for T1-ATM).

average rate—Calculate according to the 
maximum number of calls the PVC will carry 
times the bandwidth per call. The following 
formulas give you the average rate in kbps:

For VoIP:

G.711 with 169 or 80 byte sample size: max calls 
x 128K

G.726 with 40 byte sample size: max calls x 85K

G.729a with 10 byte sample size: max calls x 85K

For VoAAL2:

G.711 with 40 byte sample size: max calls x 85K

G.726 with 40 byte sample size: max calls x 43K

G.729a with 30 byte sample size: max calls x 15K

If voice activity detection (VAD) is enabled, the 
bandwidth usage is reduced by as much as 
12 percent with the maximum number of calls in 
progress. With fewer calls in progress, bandwidth 
savings are less.

burst— Set the burst size as large as possible, and 
never less than the minimum burst size. Guidelines 
are as follows:

The minimum burst size is 4 times the number of 
voice calls.

The maximum burst size is the maximum allowed 
by the carrier.

You can calculate the value using the calculator at 
the following URL:

http://www-vnt/SPUniv/DSP/Codec_Calc1.asp

Router(config-if-atm-vc)# vcci pvc-identifier

Assigns a unique identifier to the PVC.

Router(config-if-atm-vc)# exit

Exits ATM virtual circuit configuration mode.

Router(config-if)# exit

Exits interface configuration mode.

Router(config)# dial-peer voice number pots

Enters dial-peer configuration mode for the POTS dial 
peer.

Router(config-dial-peer)# application MGCPAPP

Initiates MGCP for the voice ports.

You can enter the MGCPAPP keyword in either 
uppercase or lowercase.