Silent Retry for Voice Session Fallback in 5G Networks
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Solution Overview
Problem
The transition from 4G LTE to 5G standalone architecture is expected to take years, resulting in heterogeneous telecommunication networks, where EPS fallback calls are prone to issues like long UE response times, leading to dropped calls due to unsuccessful voice session establishment in legacy systems.
Innovation Solution
Implementing a silent retry procedure by UE or TAS using specific error codes and timeouts to automatically reattempt establishing voice sessions in EPS instead of transitioning back to 5G, ensuring seamless communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If EPS fallback is used to support legacy devices and voice sessions, then compatibility with legacy systems is improved, but call success rate deteriorates due to UE response timeouts and session establishment failures
Solution Approach 1:
The system performs preliminary actions by detecting EPS fallback session failures before the call is fully established, then proactively triggers a retry mechanism. The UE or network side detects the failure condition (timeout or error code) and automatically initiates a new voice session establishment attempt in EPS, preventing the call from proceeding in a failed state and improving overall call success rate while maintaining legacy system compatibility
Solution Approach 2:
The system implements feedback by monitoring the outcome of EPS fallback voice session establishment attempts. When a failure is detected (through timeout or error code reception), this feedback triggers an automatic retry mechanism. The system continuously monitors retry outcomes and can terminate further retries after a configurable number of attempts, creating a closed-loop control system that adapts to network conditions and improves call reliability
2Reliability
If automatic retry mechanism is implemented to improve call success rate, then reliability is improved, but network stress and resource consumption worsen
Solution Approach 1:
The system applies partial action by implementing selective retry only for specific failure conditions (EPS fallback voice session failures) rather than all call failures. The retry mechanism is triggered only when specific error codes or timeout conditions are detected, avoiding unnecessary retry attempts that would waste network resources. Additionally, the retry count is limited to a configurable maximum, preventing excessive action that would overload the network
Solution Approach 2:
The system changes parameters by making the retry behavior configurable through network parameters. The maximum number of retry attempts, timeout thresholds, and error code mappings can be adjusted by the network operator to optimize performance under different network conditions. This parameter flexibility allows the system to adapt retry intensity to match network capacity, improving reliability while controlling network stress
3Ease of operation
If UE waits for network response during EPS fallback procedure, then protocol compliance is improved, but response time worsens causing call drops
Solution Approach 1:
The UE performs preliminary actions by proactively detecting EPS fallback failures and initiating retry before the normal protocol timeout would cause call termination. Instead of passively waiting for the network to timeout and terminate the call, the UE actively monitors for failure conditions and takes preemptive action to reestablish the session, reducing effective response time while maintaining protocol compliance
Solution Approach 2:
The UE implements self-service by autonomously detecting EPS fallback failures and triggering retry mechanisms without requiring network intervention or additional signaling. The UE independently monitors its own response times, detects failures based on configured thresholds, and autonomously initiates retry procedures, eliminating the need for extended waiting periods while maintaining protocol compliance
Data Source
AI summary
Techniques and systems for selectively implementing a silent retry procedure after a voice session has moved from a preferred IP-based system (e.g., 5GS) to a legacy IP-based system (e.g., EPS) are disclosed. The silent retry procedure may be implemented by a UE and/or by a TAS using one or more specific error codes and/or timeouts. In this manner, after a voice session has been redirected or handed over from a preferred system (e.g., 5GS) to a legacy system (e.g., EPS), and based on an issue arising that prevents the voice session from being successfully established thereafter, the UE or the TAS may reattempt to establish the voice session directly in the legacy system, instead of allowing the UE to transition back to the preferred system (e.g., 5GS) after a session failure in the legacy system, which increases the overall success rate of establishing voice sessions.