Hi Andrea,
Prior to CallManager 3.3, intercluster trunks are implemented as H.323 gateways. On the 3.1 CallManager, you can configure a H.323 gateway that uses Intercluster-Trunk as the Device Prototcol (instead of H.225). For its Device Name, use the IP address of the 3.3 Callmanager. You can then configure a Route Pattern that handles calls destined to the patterns on the 3.3 server, and point that to the new H.323 gateway.
CallManager 3.3 supports three types of trunks for intercluster and H.323 communications:
Intercluster trunks
H.225 Gatekeeper-Controlled Trunk
Intercluster Gatekeeper-Controlled Trunk
In your case, you should use Inter-Cluster Trunk (Non-GateKeeper Controlled). For its Device Name, use the IP address of the 3.2 Callmanager. You then configure a Route Pattern that matches calls destined to the patterns on the 3.2 server, and point that to the new Inter-Cluster Trunk.
Regards,
Michael.