Department of Information Engineering
Voice over IP (VoIP) and multimedia real-time communications between two are more parties are widely used over the Internet. The Session Initiation Protocol (SIP) is the current signaling standard for such applications and allows users to establish and negotiate any end-to-end multimedia session. Unfortunately current SIP-based platforms use a centralized architecture where calls between User Agents (UAs) are routed based on static public-reachable proxy servers, suffering of well-known scalability and availability problems. Moreover security is currently poorly implemented and, when supported, it usually relies on a third-party trust relationship or on a Public Key Infrastructure (PKI).