I"ve codecs registered as H323 on VCS. these codecs aren't able to call other endpoints that aren't registered as h323 on the vcs. this codec also isn't able to do IP call to other codecs.
If this is VCS Expressway (or standalone VCS Control deployment) which should make a IP addressing call directly, then you should configure “Direct” for “Call to unknown IP addresses” under “VCS configuration > Dial plan > Configuration” of Web GUI (like what Dharmesh mentioned already).
If this is VCS Control and have traversal link between VCS Expressway, but making a call to other H323 Endpoint in same local network, then
VCS Control now know direct reachable network and will make direct H.323 IP address based call, if destination IP address is within what has configured as subzone.
Are the other codecs which are registered, but not using h323, SIP registered instead?
Can you check what the Interworking setting is set to - it should be ok as long as it isn't set to off.
Also can you check that the search rule that will target these endpoints is adding the sip domain to the destination alias if the h323 endpoints aren't dialling that.
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