SIP

Session Initiation Protocol (SIP) is a protocol used in VoIP platforms to initiate and manage call sessions. SIP is considered a call initiation protocol.

SIP technology also enables SIP trunking, a service that allows on-premise PBX networks to connect to VoIP services for outbound calls rather than being restricted to traditional telephony networks.

For a more in-depth look, check out: What is SIP Communication? Everything You Need to Know