A session border controller (SBC) is a device or application that governs the manner in which calls, also called sessions, are initiated, conducted and terminated in a VoIP (Voice over Internet Protocol) network. An SBC can be placed in the communication path between any two parties engaged in a VoIP session. A common location for a stand-alone SBC is a connection point, called a border, between a private local area network (LAN) and the Internet.
An SBC can exist as a single, independent hardware unit containing all of the resources necessary for call signaling and call control. Alternatively, the signaling and control functions can be divided between the communicating systems.
An SBC can facilitate VoIP sessions between phone sets or proprietary networks that use different signaling protocols. In addition, an SBC can include call filtering, bandwidth use management, firewalls and anti-malware programs to minimize abuse and enhance security. An SBC can act as a router and conceal the internal topology of a private network from the external environment. However, regulations demand that SBCs allow interception and monitoring of communications for law enforcement purposes. Emergency calls are given top priority so they can be completed under all network traffic conditions.