A Session Border Controller is a network element that provides security and interoperability between differing SIP-based networks, managing signialling and occasionally media transport. The SBC enforces security, quality of service and admission control mechanism over the VoIP sessions. SBCs are used in a number of network situations: Between service providers (peering SBC), access into a service provider (access SBC) or at a customer's site (enterprise SBCs)
Enterprise session border controllers are increasingly being packaged as part of a larger sale of unified communications (UC) and contact center solutions in conjunction with SIP trunking.