Emergency Call Back via Intersystem Paging Identifier
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Solution Overview
Problem
Current solutions for emergency call back to a wireless unit that has moved into a border system are time-consuming, especially when the mobile directory number (MDN) is unknown, and there is no effective method for handling situations where the MDN is not registered or the wireless unit lacks a SIM/R-UIM, leading to difficulties in reconnecting emergency calls across different serving systems.
Innovation Solution
A unique call back number is generated and recorded at the original serving system and PSAP, which includes a mobile switching center identifier, allowing the PSAP to page the wireless unit through intersystem paging, ensuring emergency call back even when the unit has roamed to a border system, and updating this number as necessary to maintain connectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the emergency call back is routed through the wireless unit's home system using existing standards, then the call can be delivered to the border system, but the process becomes time-consuming especially for international roamers or systems separated by great distances
Solution Approach 1:
The patent introduces a border system as an intermediary that directly pages the wireless unit in the border system's coverage area, bypassing the need for routing through the home system. The border system receives the emergency call back request and directly pages the wireless unit using its identifier, significantly reducing call back time for roaming units.
2Adaptability or versatility
If the wireless unit has no MDN or MSID registered (new phone, expired subscription, or no SIM/R-UIM), then the unit can still place emergency calls, but there is no solution for call back since no identifier is known to the serving system or PSAP
Solution Approach 1:
The patent performs preliminary action by assigning a temporary identifier to the wireless unit at the time of the emergency call setup. This temporary identifier is stored in both the PSAP and the serving system before the call is dropped, ensuring that call back is possible even though the unit has no permanent MDN or MSID registered.
Solution Approach 2:
The patent uses a temporary, short-lived identifier assigned only for the duration of the emergency call and call back process. This disposable identifier enables call back functionality without requiring permanent registration or a SIM/R-UIM in the wireless unit.
3Ease of operation
If the wireless unit moves from the original serving system coverage area to a border system coverage area, then the unit remains reachable for normal service, but the original serving system cannot directly page the unit for call back
Solution Approach 1:
The patent makes the border system multi-functional by enabling it to both provide normal wireless service to roaming units and handle emergency call back paging. The border system receives emergency call back requests from the original serving system and directly pages units in its coverage area, combining routing and paging functions.
Data Source
AI summary
In the method, a paging identifier for a wireless unit is obtained using a unique call back identifier for an emergency call placed by the wireless unit in response to an emergency call back. Then, an emergency intersystem page, which provides the paging identifier of the wireless unit and identifies the emergency intersystem page as requesting paging of the wireless unit for an emergency call back, is sent.