SBC (Session Border Controller)

A network device at the edge of a VoIP network that provides security, NAT traversal, codec transcoding, and SIP normalization for voice traffic. SBCs hide the internal network topology, protect against SIP-based denial of service attacks, and interoperate with non-compliant SIP endpoints. They also handle media anchoring to ensure RTP flows through the controlled network for lawful intercept and billing. Most enterprise SIP trunks and carrier interconnects use an SBC at the boundary.