Session border elements are responsible for policing connections. The simplest session border element is a VoIP-aware firewall, an Application-Level Gateway (ALG). Some functions that can be present in a session border element includes signaling and media gateway operations, firewall functions, NAT functionality, and encryption or VPN support. In SIP/IMS, these elements are called Session Border Controllers (SBCs) or security gateways.
BorderNet Session Border Controller
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