The Call Control API defines an easy-to-use interface for 1st-party Call Control. With this interface, an application can make, receive, transfer, hangup, and perform other operations on calls using 4 telephony protocols: SIP, H.323, CTI, or SCCP. However, from the perspective of the developer using the API, the protocol used is irrelevant and hidden from the developer. The protocol actually used is decided how the Application Server is deployed; not how the application is written.