The public switched telephone network (PSTN) is a traditional, circuit-switched network that is optimized for real-time voice communication. When you call someone, you close a switch by dialing and establish a circuit with the other party. The PSTN guarantees quality of service by dedicating the circuit to your call until you hang up the telephone. Whether you and your party are talking or silent, you continue to use the same circuit until you hang up.
Telephony services in Windows Vista and Windows Server 2008 enable programs to communicate easily over the traditional telephone network. Telephony server provides support for the direct connection to a PSTN network, automatic phone dialing, and interfaces for conference calling, voice mail, and caller ID.
Telephony services helps make the Windows Vista and Windows Server 2008 operations systems a powerful and flexible platform for developing and using computer-telephony integration (CTI) programs. Programs can build on the Telephony service client-server support to provide a graphical interface for system administration and enhanced services, such as voice mail, call queuing, call forwarding, telephony-computer integration, and speech recognition. Besides enabling individual programs to provide telephony services, the Telephony service manages the telephony devices, so that more than one program using a line can remain active simultaneously. One program can wait for a call while another is dialing out.
In a client-server environment, telephony can be managed like any other network service. You can specify the lines and phones available to specific users and use domain security to control access to telephony resources. Telephony service providers and all stored parameters can be updated across a LAN, making it easy to set up, use, and manage resources without regard to physical location.