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:
“Currently, U.S. society has been encouraged by its political and subsidized mass-media intelligentsia to view U.S. life as a continual “morning in America” paradise, where the only social problems occur in the inner cities. Psychologists call this denial.”
—Ishmael Reed (b. 1938)
“The admission of the States of Wyoming and Idaho to the Union are events full of interest and congratulation, not only to the people of those States now happily endowed with a full participation in our privileges and responsibilities, but to all our people. Another belt of States stretches from the Atlantic to the Pacific.”
—Benjamin Harrison (1833–1901)
“The glance is natural magic. The mysterious communication established across a house between two entire strangers, moves all the springs of wonder. The communication by the glance is in the greatest part not subject to the control of the will. It is the bodily symbol of identity with nature. We look into the eyes to know if this other form is another self, and the eyes will not lie, but make a faithful confession what inhabitant is there.”
—Ralph Waldo Emerson (1803–1882)