We have a non-gatekeeper controlled intercluster trunk setup between a 6.1.3 cluster (clusterA) and a 4.1.3 cluster (clusterB). The phones and the Intercluster trunks in each cluster are in separate regions and the codec between these regions are set to G729. When I place a call from clusterA to device in clusterB the phone in clusterA is communicating using a G711 codec and the phone in clusterB is communicating using a G729 codec. If we use wireshark to look at this call we see a transcoding resource in clusterA involved in this call. When I place a call from clusterB to device in clusterA the phone in clusterB is communicating using a G711 codec and the phone in clusterA is communicating using a G711 codec. If we use wireshark to look at this call we see a transcoding resource in clusterA involved in this call.
When we setup a non-gatekeeper controlled intercluster trunk between two 6.1.3 clusters using the same configurations parameters, the calls no matter who initiates the call uses a G729 codec on both side with no transcoding resource involved. Any ideas as to what could be causing this?