VoIP glossary · Session Border Controller
What is SBC?
An SBC (Session Border Controller) is a security and interoperability device that sits at the edge of a voice network, controlling which SIP traffic gets in and fixing incompatibilities between systems.
SBC explained
Think of an SBC as a firewall that understands SIP. It hides internal addresses, handles NAT, enforces call limits, blocks scanners and malformed messages, and can transcode or rewrite headers so two different systems can talk to each other.
Carriers run SBCs at every interconnect. Enterprises use them in front of their PBX, especially with Microsoft Teams Direct Routing or several trunks from different providers. Open-source options such as Kamailio with RTPengine can fill the same role.
Example
A company puts an SBC between its CUCM cluster and the SIP trunk. The SBC converts between CUCM’s internal numbering and E.164 and blocks INVITEs from unknown IPs.
Put it into practice
Prepaid SIP trunks and wholesale routes from $200. Ask sales for rates or the NOC for a technical answer.