IP telephony

Definition of IP telephony in The Network Encyclopedia.

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What is IP Telephony?

An umbrella term for technologies that allow the transmission of voice and video over TCP/IP internetworks instead of the traditional Public Switched Telephone Network (PSTN). Many vendors have produced platforms and software for IP telephony, but the technology is still in its growth stage and standards are not yet clearly established.

The advantage of IP telephony is that it allows voice communication to be closely integrated with data transmission over corporate networks and allows long-distance communication to be established over the Internet instead of through private long-distance carriers such as Sprint and MCI WorldCom.

The primary difficulty with IP telephony is that the existing Internet Protocol (IP) internetwork is connectionless and suffers from latency that can cause annoying glitches (pauses) in voice and video transmission over IP packets.

This happens because TCP/IP was not originally designed as a connection-oriented service capable of specific levels of quality of service (QoS), whereas the PSTN, with its circuit-switched connections, provides just that.