Routing Mechanism for Emergency Calls in the Visited Voice Network

The emergency call service is a fundamental part of real-time communication. Emergency calls initiated by UEs are forwarded to the nearest PSAP (Public Safety Answering Point) based on their visited network location. However, in the IMS (IP Multimedia Subsystem) network, when a subscriber moves from the home network (area B) to the visited network (area A), and dials an emergency call, the signaling traffic traverses the home network before reaching the PSAP in the visited network. Above all, excessive signaling overhead and delay are introduced. Moreover, emergency calls may fail in disaster scenarios where long-distance links are disrupted. To address these issues, this paper proposes an IDR (IMS Dual Registration) strategy, which enables emergency call routing in the visited voice network, reducing transmission delay and improving service availability.