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:
“One day my mother called me ... and she said, “Forty-nine million Americans saw you on television tonight. One of them is the father of my future grandchild, but he’s never going to call you because you wore your glasses.””
—Lesley Stahl (b. 1941)
“For the mother who has opted to stay home, the question remains: Having perfected her role as a caretaker, can she abdicate control to less practiced individuals? Having put all her identity eggs in one basket, can she hand over the basket freely? Having put aside her own ambitions, can she resist imposing them on her children? And having set one example, can she teach another?”
—Melinda M. Marshall (20th century)