A Session Border Controller (SBC) is a network component for safe coupling of different computer networks or computer networks with different security requirements. SBC are mainly used in IP telephony networks (VoIP) to connect external (insecure) data networks with internal (secure) IT structures or to implement so-called sessions.

An SBC enables control and monitoring of signaling and media streaming as well as setup, execution and termination of telephone conversations or other interactive media that are involved in a communication.

An SBC is, as the name implies, used at network boundaries and couples internal and external networks. The SBC analyzes the various data streams (sessions) and acts on the different data streams (here: media data or signaling data) depending on the configuration. Within the telecommunications area (VoIP) signaling data and voice / video data are transmitted separately.

In general a SIP-based phone sends the signaling data to the telephone system, while the voice data is usually transmitted via the shortest route directly from phone to phone. By decoupling of signaling and voice data on the one hand the advantages of IP-based data networks can be used but on the other hand, the transmission of voice (media) data cannot be affected by the telephone system.