H.323 and SIP are both IP protocols for calls. H.323 is older. Your settings should indicate whether H.323 or SIP is enabled/disabled. If you're just dialing IP addresses for calls, it most likely is H.323. The User/Admin Guides for the HDX and VSX detail the ports used for H.323 calls. You may also do WireShark packet captures to see the call attempts and traffic. This should show what port connections are being requested and the responses, if any.