you need to do before an endpoint can place or receive H.323 calls using a URI address?

What do you need to do before an endpoint can place or receive H.323 calls using a URI address?

A.
Register the endpoint to the SIP server.

B.
Register the endpoints to the gatekeeper.

C.
Register the endpoint to the gateway.

D.
Register the endpoint to the Cisco TelePresence MCU.