A Session Border Controller (SBC) is a network device that manages and secures voice and video communication sessions over the internet. It acts as a gatekeeper, ensuring that calls are properly routed and that the quality of service is maintained. SBCs help prevent unauthorized access and protect against various types of attacks, such as denial-of-service. In addition to security, SBCs also handle protocol translation, enabling different communication systems to work together seamlessly. They can optimize bandwidth usage and improve call quality by managing network traffic. Overall, SBCs play a crucial role in modern VoIP (Voice over Internet Protocol) communications.