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. Common examples of such features are “Call Waiting”, “Call Forward on Busy”, and “Do Not Disturb”.
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 called as call processing.
In telecommunication, the term call processing has the following meanings:
- The sequence of operations performed by a switching system from the acceptance of an incoming call through the final disposition of the call. See call control for a more complete description.
- The end-to-end sequence of operations performed by a network from the instant a call attempt is initiated until the instant the call release is completed.
- In data transmission, the operations required to complete all three phases of an information transfer transaction.