Session Initiation Protocol (SIP) trunking is a service offered by a communications service provider that uses the protocol to provision voice over IP (VoIP) connectivity between an on-premises phone system and the public switched telephone network (PSTN).
SIP is used for call establishment, management and teardown. SIP trunking is typically sold as a replacement for digital Primary Rate Interfaces (PRIs), which are based on time-division multiplexing (TDM).
SIP trunking is widely deployed by communications service providers across the globe, many of which are using it to replace their TDM-based services. By delivering SIP trunking over existing Ethernet or Multiprotocol Label Switching (MPLS) network infrastructure, the providers reduce the cost and management complexity associated with legacy digital platforms, while also provisioning additional features.