We have a intercluster trunk configured from CCM 6.0 to CCM 8.0; where some phones are registered on CCM 6.0 and other phones are registered on CCM 8.0.
When we call from phone registered on CCM 6.0 to CCM 8.0 call is happening and voice is flowing through the Trunk.
But when we try calling from phone registered on CCM 8.0 to CCM 6.0 sometimes the call is landing but voice does not flow and sometimes its just shows processing and call does not proceed.
( Both the CCM's are connected on the same zone without any firewall.)
Kindly Update what could be the problem.