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:
“The welcome house of him my dearest guest.
Where ever, ever stay, and go not thence,
Till natures sad decree shall call thee hence;
Flesh of thy flesh, bone of thy bone,
I here, thou there, yet both but one.”
—Anne Bradstreet (c. 1612–1672)
“Powerful, yes, that is the word that I constantly rolled on my tongue, I dreamed of absolute power, the kind that forces others to kneel, that forces the enemy to capitulate, finally converting him, and the more the enemy is blind, cruel, sure of himself, buried in his conviction, the more his admission proclaims the royalty of he who has brought on his defeat.”
—Albert Camus (1913–1960)
“The mind is the greatest of all human forces. Control the mind and you control the body.”
—Griffin Jay, Randall Faye, and Lew Landers. Armand Tesla (Bela Lugosi)