A Session Border Controller (SBC) is a critical component in telecommunications, securing Voice over IP (VoIP) infrastructures and enabling interoperability among different signalling messages and media flows. Deployed in both enterprise and carrier networks, SBCs manage demarcation points between users and service providers, ensuring the security of communication sessions. 

Originally supporting various signalling types, modern SBCs primarily focus on securing SIP infrastructures. They play a crucial role in providing interworking between protocol versions and optional headers, enhancing security through ingress Access Control Lists (ACLs), rate limiting, and message processing. 

SBCs also handle media traffic, ensuring the security of Real-Time Transport Protocol (RTP) flows and allowing for transcoding. In contemporary implementations, signalling and media components are decoupled for greater flexibility and scalability, aligning with the IP Multimedia System (IMS) reference architecture.