IMS Emergency Call Routing for Inbound Roaming Continuity
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Solution Overview
Problem
Travelers using their mobile devices in foreign countries often face emergency call failures due to unfamiliar local emergency numbers, as their home networks may not recognize the numbers they dial, leading to failed connections with public safety answering points (PSAPs).
Innovation Solution
An Internet Protocol (IP) multimedia subsystem (IMS) node is configured to receive call requests from inbound roaming UEs, determine if the called party identifier corresponds to an emergency number associated with the UE's home network, and route the call to the appropriate public service answering point (PSAP) by adding or replacing the number with a local equivalent emergency number.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If travelers use their home emergency numbers while roaming abroad, then they can dial familiar numbers, but the visited network cannot recognize these numbers and the emergency call fails
Solution Approach 1:
The visited network acts as an intermediary by detecting when a roaming user dials their home emergency number and automatically translating it to the local emergency number. This mediator function resolves the contradiction by allowing users to dial familiar numbers while ensuring the local network can recognize and route the call appropriately.
Solution Approach 2:
The system changes the called party identifier parameter dynamically. When an emergency call is detected from a roaming user, the system modifies the dialed number from the home country emergency number to the visited country's emergency number, enabling successful call routing while maintaining user convenience.
2Reliability
If the visited network uses only local emergency numbers, then emergency calls work reliably for local users, but roaming users cannot use their familiar emergency numbers
Solution Approach 1:
The emergency number mapping system is dynamic rather than static. It automatically detects when a user is roaming and adapts by translating their home emergency number to the local number. This dynamic behavior allows the system to maintain reliability for local users while becoming adaptable to accommodate roaming users' needs.
Solution Approach 2:
The system performs preliminary detection and translation of emergency numbers before the call is routed. By identifying roaming status and translating the emergency number in advance, the system ensures both reliability for local users and compatibility for roaming users without requiring changes to user behavior.
3Reliability
If the network translates emergency numbers for roaming users, then emergency call continuity is maintained, but the network complexity increases
Solution Approach 1:
The network performs self-service by automatically detecting roaming status and emergency call attempts, then autonomously translating the emergency number without requiring external intervention or complex manual configuration. This self-service approach maintains emergency call continuity while limiting complexity growth through automated rather than manual processes.
Data Source
AI summary
Described herein is an Internet Protocol (IP) multimedia subsystem (IMS) node configured to receive a call request from an inbound roaming user equipment (UE) and determine that a called party identifier in the call request corresponds to an emergency number. The emergency number is associated with geographic entity in which a home network of the inbound roaming UE is located. In response to the determining, the IMS node sends the call request to an emergency call session control function (E-CSCF) for routing to a public service answering point (PSAP).