Call Admission Control (CAC) prevents oversubscription of VoIP networks. It is used in the call set-up phase and applies to real-time media traffic as opposed to data traffic. CAC mechanisms complement and are distinct from the capabilities of Quality of Service tools to protect voice traffic from the negative effects of other voice traffic and to keep excess voice traffic off the network. Since it averts voice traffic congestion, it is a preventive Congestion Control Procedure. It ensures that there is enough bandwidth for authorized flows.
Integrated Services with RSVP (which reserve resources for the flow of packets through the network) using controlled-load service ensures that a call cannot be set up if it cannot be supported. CAC rejects calls when either there is insufficient CPU processing power, the upstream and downstream traffic exceeds prespecified thresholds, or the number of calls being handled exceeds a prespecified limit.
Connection Admission Control (CAC) can be used to prevent congestion in connection-oriented protocols such as ATM. In that context, there are several schemes available. However, VoIP differs in that it uses RTP, UDP and IP, all of which are connectionless protocols.
Famous quotes containing the words call, admission and/or control:
“People who love only once in their lives are ... shallow people. What they call their loyalty, and their fidelity, I call either the lethargy of custom or their lack of imagination. Faithfulness is to the emotional life what consistency is to the life of the intellect—simply a confession of failures.”
—Oscar Wilde (1854–1900)
“To be rich is to have a ticket of admission to the masterworks and chief men of each race. It is to have the sea, by voyaging; to visit the mountains, Niagara, the Nile, the desert, Rome, Paris, Constantinople: to see galleries, libraries, arsenals, manufactories.”
—Ralph Waldo Emerson (1803–1882)
“We long for our father. We wear his clothes, and actually try to fill his shoes. . . . We hang on to him, begging him to teach us how to do whatever is masculine, to throw balls or be in the woods or go see where he works. . . . We want our fathers to protect us from coming too completely under the control of our mothers. . . . We want to be seen with Dad, hanging out with men and doing men things.”
—Frank Pittman (20th century)