Emergency Call Routing in Mobile IP Networks
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Solution Overview
Problem
Third-generation Mobile IP Telephony networks face challenges in providing seamless access to location-based services and emergency calls for roaming subscribers, as they often lack the necessary location information to route calls effectively, especially in UMTS standard-based networks.
Innovation Solution
The system employs a mechanism where the Gateway GPRS Service Node provides the address of a Call State Control Function, which selects a Public Safety Answering Point based on Service Area Identification, allowing emergency calls to be routed without authentication or billing, and transfers the subscriber's approximate geographic location to facilitate connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If IP Telephony subscribers use voice call services in their home network while roaming, then they can access location-based services, but they cannot make emergency calls in the visited network without additional location information
Solution Approach 1:
The patent introduces a Location Services Switching Function (LSSF) as an intermediary component that mediates between the visited network and the home network. The LSSF receives emergency call requests from visited network call control entities, obtains location information from the visited network, and forwards the calls to appropriate PSAPs. This intermediary enables emergency call capability for roaming subscribers without requiring them to have location-based services activated in their home network.
Solution Approach 2:
The patent implements preliminary action by having the LSSF proactively obtain location information from the visited network before the emergency call is fully routed. The LSSF requests location information when it receives an emergency call request, and this location information is used to select the appropriate PSAP. This preliminary acquisition of location data enables the system to handle emergency calls even when the subscriber's home network does not have location-based services configured.
2Ease of operation
If the system provides emergency calls without authentication or billing, then accessibility is improved, but fraud risk increases
Solution Approach 1:
The patent implements feedback mechanisms where the LSSF receives and processes feedback information from the visited network about the subscriber's location and call status. The system uses this feedback to dynamically select PSAPs and manage call routing. The feedback loop also includes monitoring the call flow to ensure proper authentication and billing controls are maintained despite the simplified access process.
Solution Approach 2:
The LSSF acts as an intermediary that maintains security and fraud prevention controls while providing easy access. It performs authentication and billing management functions, acting as a buffer between the simple access mechanism and the secure core network. The LSSF ensures that emergency calls are properly authenticated and billed according to network policies while still allowing seamless access for roaming subscribers.
3Reliability
If location information is obtained from the visited network, then emergency calls can be routed correctly, but network complexity increases
Solution Approach 1:
The LSSF is designed as a multi-functional component that performs multiple tasks: receiving emergency call requests, obtaining location information from the visited network, selecting PSAPs, and forwarding calls. By consolidating these functions into a single universal component, the patent reduces overall network complexity compared to having separate specialized components for each function. The LSSF's multi-functionality allows it to handle various call types and scenarios through a unified approach.
Solution Approach 2:
The LSSF serves as an intermediary layer between the visited network and the home network's core services. It handles the complexity of location information exchange and PSAP selection centrally, shielding the rest of the network from these complexities. This intermediary approach allows the network to maintain simple interfaces with visited networks while managing the complexity internally through standardized protocols and procedures.
Data Source
AI summary
An emergency telephone call is supported and routed to a Public Safety Answering Point (PSAP) in an IP based packet switched wireless communications network. An activate PDP context request is sent from a user equipment to the network. A parameter in the activate PDP context request indicates that the PDP context will be used to transfer an emergency call. An activate PDP context accept message is returned from the support node to the user equipment. The activate PDP context accept message acknowledges the activate PDP context request message and provides the address of a call state control function. A call setup request transferred to the call state control function includes the Service Area Identity (SAI). The call state control function selects a PSAP based, at least in part, on the SAI included in the call setup request and forwards the emergency call to the selected PSAP.