g729 - when do I need a license?

Here is the setup I an contemplating:

qty 7 * BT200’s <–> Asterisk <–> 512k up connection <–> CallCentric <-> PSTN

The BT200 and CallCentric both support g729. My concern is the limited amount of bandwidth available. Here are two scenarios that concern me.

Scenario #1:
PSTN customer will call someone at my friend’s office. The call hits the Asterisk box, realizes that all phones are busy so it forwards the call back out through CallCentric to another PSTN phone.

PSTN calls in -> CallCentric -> DSL connection -> Asterisk -> (everyone on the phone) -> DSL Connection -> CallCentric -> PSTN

CallCentric indicates support for g729. Can I configure Asterisk to require g729 to reduce bandwidth requirements? If so then do I need a license for every channel in this specific scenario? How about when a BT200 calls to check their voicemail stored on the Asterisk server?

Scenario #2:

Grandstream BT200 -> Asterisk -> DSL -> CallCentric -> PSTN

I assumed since the BT200 supports g729 and CallCentric supports g729 then Asterisk is simply acting as a pass-thru server. Am I correct? If so then do I need to make any special modifications outside of sip.conf to make sure g729 is used for all calls? Is there any way to confirm/deny g729 is being used?

If I am missing anything then I would greatly appreciate any knowledge you are willing to share.

Scenario #1:


I think you don’t need, g729 passthrough should be enough but this depends on your dialplan configuration.

In this case a g729 license is required if codec used is g729.

Scenario #2:

Yes but this depends on your dialplan configuration, I mean depends on the dialplan applications used.


The CLI command “sip show channels” shows the used codec for every active channel.


Marco Bruni