UE IMS Registration Fallback for Voice Service Reliability
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Solution Overview
Problem
In evolved packet system (EPS) mobile communication systems, there is no guarantee that a user equipment (UE) will initiate IMS registration or successfully register for voice services, leading to potential failures in IMS registration and inadequate voice service access, especially when the UE's voice setting is set to 'IMS PS voice only' or 'IMS voice preferred, CS voice secondary', and the network indicates 'IMS Voice over PS session supported'.
Innovation Solution
The UE is configured to trigger IMS registration with proper indicators for voice services when the network provides a 'IMS Voice over PS session supported' indication, and if IMS registration fails, it attempts a combined registration procedure for CSFB or retries IMS registration, depending on the UE's usage setting, to ensure voice service access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE is configured to automatically initiate IMS registration when network indicates 'IMS Voice over PS session supported', then voice service access is improved, but device complexity and signaling overhead increase due to additional registration procedures
Solution Approach 1:
The UE performs preliminary actions by proactively initiating IMS registration when it receives the 'IMS Voice over PS session supported' indication from the network, rather than waiting for voice service requests. This preliminary registration ensures voice service availability is established in advance, improving reliability while the complexity is managed through conditional triggers based on network indications and UE usage settings.
Solution Approach 2:
The registration behavior is made dynamic through configurable UE usage settings ('Voice Centric', 'Data Centric', 'Data Only') that allow the UE to adapt its registration behavior based on user preferences and service requirements. The UE dynamically adjusts whether to initiate IMS registration, attempt combined registration, or refrain from registration based on the combination of network capabilities and configured settings, balancing reliability improvements with complexity management.
2Reliability
If the UE attempts multiple alternative registration methods (combined registration, retry IMS registration) when initial IMS registration fails, then voice service availability is improved, but loss of time and increased signaling overhead occur
Solution Approach 1:
The UE prepares alternative registration strategies in advance by configuring usage settings that define fallback behaviors. When initial IMS registration fails, the UE executes pre-planned alternative actions (combined registration for CSFB, or retry IMS registration) based on its usage setting, improving registration success rate while minimizing decision time through pre-configured policies.
Solution Approach 2:
The UE applies partial action by selectively attempting alternative registration methods only when initial IMS registration fails and only based on specific usage settings. Not all UEs will attempt all alternative methods - the action is partial and conditional, reducing overall time loss and signaling overhead while still improving registration success rates for UEs that require voice services.
3Adaptability or versatility
If the UE is configured with 'Voice Centric' usage setting and IMS registration fails, then voice service access is maintained through CSFB, but device complexity and network signaling increase
Solution Approach 1:
The UE implements multi-functionality by supporting both IMS-based voice services and CSFB (Circuit Switched Fallback) within a single device architecture. The usage setting mechanism allows the UE to universally handle different voice service access methods (IMS only, IMS with CSFB fallback, or CSFB preferred) based on network capability indications and user preferences, providing adaptability while managing complexity through unified configuration.
Solution Approach 2:
The UE dynamically switches between different voice service access modes (IMS registration, combined registration for CSFB) based on real-time network conditions and configured usage settings. This dynamic behavior allows the UE to adapt to available network capabilities and maintain voice service access flexibility while managing complexity through policy-based decision-making rather than hard-coded multi-mode management.
Data Source
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AI summary
A method for user equipment, UE, in a mobile communication system is disclosed. The method comprises receiving at the UE a Non Access Stratum, NAS, protocol response message with a network provided Voice over IP Multimedia Core Network Subsystem, VoIMS, indicator. The UE has a UE usage setting being one of a preference of the UE for voice service, a preference of the UE for data service or Data Only meaning that the UE requires only data services and can accept that there is no voice service. The NAS protocol response message is an accept message. The method further comprises if the VoIMS indicator indicates that VoIMS is supported, attempting IMS registration and if IMS registration fails, responsive to the UE usage setting indicating UE preference for voice service, selecting by the UE another radio access technology and disabling, by the UE, E-UTRA cell reselection and cell selection.