In telephony, call control refers to the software within a telephone switch that supplies its central function. Call control decodes addressing information and routes telephone calls from one end point to another. It also creates the features that can be used to adapt standard switch operation to the needs of users. These are called supplementary services and are commonly invoked by a Vertical service code. Examples include "Call Waiting", "Call Forward on Busy" etc.
Call control software, because of its central place in the operation of the telephone network, is marked by both complexity and reliability. Call control systems will typically require many thousands of person years in development. They will contain millions of lines of high level code. However they must and do meet reliability requirements that specify switch down time of only a few minutes in forty years.
The required functionality and reliability of call control is a major challenge for Voice over IP (VoIP) systems. VoIP systems are based on Internet standards and technology which have not previously attempted to satisfy such complex and demanding requirements as those that specify call control.
An alternative name often used is call processing.
Famous quotes containing the words call and/or control:
“It has become necessary to call the attention of European governments to a fact which is apparently so insignificant that the governments seem not to notice it. The fact is this: an entire people is being annihilated. Where? In Europe. Are there witnesses? One witness, the entire world. Do the governments see it? No.”
—Victor Hugo (1802–1885)
“America is not so much a nightmare as a non-dream. The American non-dream is precisely a move to wipe the dream out of existence. The dream is a spontaneous happening and therefore dangerous to a control system set up by the non-dreamers.”
—William Burroughs (b. 1914)