The RAS channel is an unreliable channel which is used to carry messages used in the gatekeeper discovery and endpoint registration processes which associate an endpoint's alias address with its call signalling channel transport address. H.225.0 recommends time-outs and retry counts for various messages as the the RAS messages are transmitted on an unreliable channel.[para] Once an endpoint or gatekeeper cannot respond to a request within the specified timeout, may use the Request in Progress (RIP) message to indicate that it is still dealing out the request. An endpoint or gatekeeper receiving the RIP resets its timeout timer and retry counter.
Registration, Admission and Status (RAS), defined in the ITU-T H.225.0/RAS, is the protocol between endpoints (terminals and gateways) and gatekeepers. The RAS is used to perform registration, admission control, bandwidth changes, status, and disengage procedures between endpoints and gatekeepers. An RAS channel is used to exchange RAS messages. This signaling channel is opened between an endpoint and a gatekeeper prior to the establishment of any other channels.
Registration, admission, and status (RAS) is a component of a network protocol that involves the addition of (or refusal to add) new authorized users, the admission of (or refusal to admit) authorized users based on available bandwidth, and the tracking of the status of all users. Formally, RAS is part of the H.225 protocol for H.323 communications networks, designed to support multimedia bandwidths. RAS is an important signaling component in networks using voice over IP (VoIP).
RAS messages are exchanged on a specific frequency called the RAS channel. The RAS channel is the first to be opened, and precedes any communications between endpoints and gatekeepers in the network. Signals in RAS can be categorized as (1) gatekeeper discovery requests and responses; (2) admission, registration, and unregistration messages and responses; (3) location requests and responses; (4) status requests and responses; and (5) bandwidth-control requests and responses.