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:
“Only what is rare is valuable.
Let no one dare to call another mad who is not himself willing to rank in the same class for every perversion and fault of judgment. Let no one dare aid in punishing another as criminal who is not willing to suffer the penalty due to his own offenses.”
—Margaret Fuller (1810–1850)
“Prayer is not asking. It is a longing of the soul. It is daily admission of one’s weakness ... It is better in prayer to have a heart without words than words without a heart.”
—Mohandas K. Gandhi (1869–1948)
“When a book, any sort of book, reaches a certain intensity of artistic performance it becomes literature. That intensity may be a matter of style, situation, character, emotional tone, or idea, or half a dozen other things. It may also be a perfection of control over the movement of a story similar to the control a great pitcher has over the ball.”
—Raymond Chandler (1888–1959)