Internet Telephony

WHAT IS IP TELEPHONY?
The terms IP Telephony, "Internet Telephony", "voice-over-IP", and "fax-over-IP" are all related and are often used as synonyms.
To be more precise, IP telephony is the collection of technologies that emulates and extends today's circuit-switched telecommunications services to operate on packet-switched data networks based on the Internet Protocol (IP). Defined in this way, IP telephony encompasses the other terms and extends those capabilities even further to include new telecommunications applications made possible by the convergence of voice and data.

Today's Public Switched Telephone Network (PSTN) provides its users with dedicated, end-to-end circuit connections for the duration of each call. Based on the calling and called parties' numbers, circuits are reserved among the originating switch, any tandem switches along the route between the two ends of the call, and the terminating switch. Signaling between these PSTN switches supports basic call setup, ...