Voice over IP (VoIP)

Voice over IP, or VoIP, refers to the transmission of voice in data packets across IP networks. Voice signals are digitised, compressed using codecs such as G.711, G.722 or Opus, and transmitted via RTP. Call setup and teardown are usually handled by the SIP protocol. Endpoints include IP phones, softphones on PCs and smartphones, and DECT systems, connected to an on-premises IP phone system or to a cloud service. Connectivity to the public network is provided through SIP trunks, following the widespread decommissioning of ISDN and analogue lines. Stable voice quality requires sufficient bandwidth, low latency, low jitter and prioritisation through quality of service. Encryption via SRTP and TLS and a backup power supply for the network equipment should also be considered.