Voice over Internet Protocol

Voice over Internet Protocol (VoIP) carries voice calls over Internet Protocol networks by encoding speech as digital data and transmitting it in packets.

Real-time Transport Protocol: A network protocol that carries real-time audio and video, typically alongside timing and sequence information. VoIP commonly uses RTP to transport encoded voice packets and preserve their order and timing.
Internet Protocol: The network-layer protocol that routes data packets between interconnected networks. VoIP depends on IP addressing and packet routing to carry calls between endpoints.
Internet telephony: Telephone service that uses Internet Protocol networks to carry calls. VoIP is the underlying technology behind Internet telephony services.
Public switched telephone network: The traditional circuit-switched telephone network used for landline voice calls. The PSTN provides the legacy circuit-switched model that VoIP can replace or interconnect with.
IP Multimedia Subsystem: An architecture for delivering multimedia services over IP networks, especially in mobile telecommunications. IMS lets telecom operators provide managed voice services using IP-based infrastructure.
Voice codec: A codec encodes and decodes speech, often compressing it for transmission or storage. Codecs determine how VoIP speech is represented, compressed, and reconstructed.
Transmission Control Protocol: A transport protocol that provides ordered, reliable delivery of data between applications. Unlike many voice media streams, TCP prioritizes reliable delivery over timely playback.
IP telephone: A telephone designed to place and receive calls using an Internet Protocol network. An IP telephone is a dedicated endpoint for making VoIP calls.
Circuit switching: A communication method that reserves a dedicated path for a connection's duration. Traditional telephony reserves circuit capacity, while VoIP shares packet network resources.
Emergency telephone number: A short telephone number that connects callers to emergency services in a jurisdiction. VoIP complicates emergency calling because location and service availability may be uncertain.

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