A Session Border Controller is typically deployed as a dedicated hardware appliance or software on a server, to control the initiation, session and termination of VoIP calls on a network. In this context, a phone call is known as a session, so a SBC controls the setup of the call between two parties and then maintains the call for the duration until the party’s hang-up, when it terminates the call.
SBCs, act to setup VoIP calls however, they can also prevent unauthorized calls and even act as a type of firewall by applying rules and access lists. As a result, SBC are typically installed in enterprise and service provider networks, in a peer-to-peer configuration to provide quality of service to VoIP calls and to provide additional security. More recently, enterprises have been installing SBC internally at departmental borders in order to provide the same levels of QoS and security but in a distributed fashion in order to spread the administration burden and also to focus the configuration. Additionally, service providers have been installing SBC at the border of their residential customer networks to provide the same functions for all their residential customers and SMBs.