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:
“But what we strive to gratify, though we may call it a distant hope, is an immediate desire; the future estate for which men drudge up city alleys exists already in their imagination and love.”
—George Eliot [Mary Ann (or Marian)
“The admission of Oriental immigrants who cannot be amalgamated with our people has been made the subject either of prohibitory clauses in our treaties and statutes or of strict administrative regulations secured by diplomatic negotiations. I sincerely hope that we may continue to minimize the evils likely to arise from such immigration without unnecessary friction and by mutual concessions between self-respecting governments.”
—William Howard Taft (1857–1930)
“... the black girls didn’t get these pills because their black ministers were up on the pulpit saying that birth control pills were black genocide. What I’m saying is that black men have exploited black women.... They didn’t want them to have any choice about their reproductive health. And if you can’t control your reproduction, you can’t control your life.”
—Joycelyn Elders (b. 1933)