 - Call admission control (CAC) is the practice or process of
regulating traffic volume in voice communications, particularly in
wireless mobile networks and in VoIP (voice over Internet Protocol,
also known as Internet telephony). Call admission control can also be
used to ensure, or maintain, a certain level of audio quality in voice
communications networks, or a certain level of performance in Internet
nodes and servers where VoIP traffic exists.
Most CAC algorithms work by regulating the total utilized
bandwidth, the total number of calls, or the total number of packets or
data bits passing a specific point per unit time. If a defined limit is
reached or exceeded, a new call may be prohibited from entering the
network until at least one current call terminates. Alternatively, a
graceful degradation methodology can be implemented. This means that
the audio quality of individual calls can deteriorate to a certain
extent before new calls are denied entry. Another method involves the
regulation of calls according to defined characteristics such as
priority descriptors. Still another method prevents new calls from
entering the network only if the resources of the central processing
unit (CPU) of a particular computer or server would be overburdened by
such calls.
Call admission control can be tricky, because the volume of
traffic in communications networks is inherently chaotic or "bursty,"
and traffic bursts are virtually impossible to predict. Another problem
is that the actual content of a call may not conform to its descriptor.
| LAST UPDATED: |
07 Mar 2008
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