We have quite a few Polycom devices registered to our expressway as SIP devices.
Previously the interworking on the expressway let us use the public IP of the expressway to call the Polycoms in an h323 format by calling publicIP##SIP extension assigned on gateway.
The h323 calls are no longer going through, but SIP calls still are. I'm not sure when it stopped working, and I'm not really sure where to look for why h323 calls won't ring through anymore.