The RAS(Registration, Admission, and Status) protocol is part of H.323 and is used for communication between a gatekeeper and a terminal, where the protocol handles registration, admission control, requesting status information, and bandwidth changes.
RAS messages are exchanged over RAS channel, which is established first, before any other channel. In RAS protocol there are several status and control messages for endpoints access in H.323 networks. So the Admission Rejection( ARJ), the Admission Request( ARQ) and the confirmation with the Admission Confirmation.
Registration, Admission, and Status (RAS) is specified in H.225 of the International Telecommunication Union( ITU-T).