Avaya CM & Asterisk - G729 issue

I have successfully tied together an Avaya CM and Asterisk instance using an H.323 trunk and G711A (alaw). I am now trying to get G729 working in order to save on bandwidth. I have a G729A codec installed and licensed from Digium on the Asterisk box (indeed this works fine between two Asterisk boxes and an IAX2 trunk).

However, when I disabled G711A on the Avaya and enabled G.729, no voice channel is created and I can not complete a call between the Asterisk and the Avaya. I tried one by one to enable G.729A, G.729AB and G.729B, but all failed. Further, no encryption is being used.

Is there some fine tuning I need to do on the Avaya side as there are some parameters (ie - silence surpression and frames per packet) to get this to work with a standard G.729A codec on the Asterisk side?