Emergency STN Handover in LTE to CS Voice Services
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Solution Overview
Problem
The existing emergency service handover method in LTE/SAE networks fails to ensure continuity of emergency voice calls due to the SCC AS in the home domain not recognizing sessions, as it relies on STN obtained from the HSS, leading to incorrect bearer establishment and handover failures.
Innovation Solution
The proposed method involves the enhanced MSC obtaining and using an emergency STN specifically configured for the visited SCC AS, ensuring the correct handover from the IMS domain to the CS domain by using the emergency STN for routing and handover purposes, thereby ensuring continuity of emergency services.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the enhanced MSC uses STN obtained from HSS for handover, then the handover procedure can be initiated, but the visited SCC AS cannot recognize the session leading to handover failure
Solution Approach 1:
The patent segments the STN into two distinct types: regular STN obtained from HSS for normal services, and emergency STN specifically configured for emergency services. This segmentation allows the system to selectively use the appropriate STN type based on service requirements, preventing the visited SCC AS from failing to recognize emergency sessions while maintaining normal handover procedures for non-emergency services.
Solution Approach 2:
The patent applies local quality by configuring specific emergency STN values in the visited domain's SCC AS that are distinct from the home domain's STN. This localized configuration ensures that the visited SCC AS can properly recognize and handle emergency sessions without being confused by home domain STN values, thereby resolving the recognition failure issue.
2Device complexity
If the system uses home domain HSS for obtaining STN, then the handover procedure is simplified, but the visited SCC AS lacks emergency service information causing bearer establishment failure
Solution Approach 1:
The patent implements preliminary action by pre-configuring emergency STN values in the visited domain's SCC AS before emergency handovers occur. This advance preparation ensures that when an emergency handover is needed, the visited SCC AS already has the correct emergency STN information ready, eliminating the need for complex real-time information retrieval and ensuring reliable emergency service continuity.
Solution Approach 2:
The patent introduces emergency STN as an intermediary element that bridges the home domain and visited domain for emergency services. This intermediary carries the necessary emergency service information from the home domain to the visited domain, enabling the visited SCC AS to properly recognize and establish bearers for emergency sessions without requiring complex inter-domain communication protocols.
3Adaptability or versatility
If the system relies on standard VCC procedures with HSS-provided STN, then general voice service continuity is achieved, but emergency service handover fails due to incorrect bearer establishment
Solution Approach 1:
The patent applies local quality by configuring specific emergency STN values in the visited domain's SCC AS that are distinct from the home domain's STN. This localized configuration ensures that the visited SCC AS can properly recognize and handle emergency sessions without being confused by home domain STN values, thereby resolving the recognition failure issue.
Solution Approach 2:
The patent changes the STN parameter specifically for emergency services by introducing emergency STN with distinct values from regular STN. This parameter change allows the system to differentiate between emergency and non-emergency handovers, enabling the visited SCC AS to properly process emergency sessions while maintaining compatibility with standard VCC procedures for regular services.
Data Source
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AI summary
An emergency service handover method is disclosed, which is applied in a single radio voice service system. A UE has established an emergency session which is anchored to a service centralization and continuity application server SCC AS at a visited location, between an IMS domain and an emergency call center via LTE/SAE network. When MSC obtains information that the UE having established the emergency session need switch to a CS domain, an enhanced MSC initiates a session establishment request to the visited SCC AS for performing a handover from the IMS domain to the CS domain on a service layer.