first it would be neccessary to know more about your deployment.
Different endpoints, different protocols, different search rules, different configuration, different networks, ...
all that can lead to different behaviror :-)
Reading here in the forum and the deployment/admin guides can help you understand over time better how
things are related to each other.
First of all, if both networks are not transparent to each other, which means routed network with not NAT,
and a whole bunch of ports open in between all components (EndpointA->VCSC-A->VCSC-B-EndpointB)
you can not use a neigbor zone out of the box as it will end up with problems.
If there is NAT or you can not open up all the needed ports directly in between endpoint A&B you will need a traversal zone in between these two networks.
If it should be a transparent network and its not working. its often a firewall, especially their L3 functionality
which breaks it.
If its a NATed or shut down firewalled network, in some scenarios calls might still get through, for example interworking
forces a traversal call, even if two VCS-C are involved. But that one thing works does not mean that this is
the right deployment.
Consider asking your Cisco Partner or an external consultant to help you on that or if you have time
read and get some courses to better understand whats going on :-)
