Telephone API Server is a general interface to enable a standard platform for interactions between various applications and telephony data. (handles all (PSTN, IP, …) telephony data) Public Switched Telephone Network (PSTN) -Plain Old Telephone Service (POTS) -regular analog phone service (analog converted to digital, then back) Internet Protocol Telephony (IPT) -transfer of digital data(voice, data, video, …) over TCP/IP networks. (Internet) Application Program Interface (API) -platform for building software applications that enable software developers to access various system resources/features without writing hardware-specific code.