An Operational Reliability Engineering Framework for Sustained High Availability in 5G Core Networks Serving Millions

The rapid global deployment of fifth-generation (5G) mobile networks has introduced unprecedented operational complexity within the 5G core, driven by cloud-native architectures, network function virtualization, software-defined networking, and ultra-low latency service requirements. Ensuring sustained high availability for 5G core networks serving millions of subscribers therefore demands a systematic operational reliability engineering approach that goes beyond traditional fault management and redundancy models. This paper proposes an Operational Reliability Engineering Framework designed to support continuous service availability, resilience, and performance stability in large-scale 5G core environments. The framework integrates reliability engineering principles with real-time observability, predictive analytics, automated fault isolation, and lifecycle-driven resilience planning across both physical and virtual network functions. Key framework components include reliability-centered design, proactive failure mode and effects analysis, service-based architecture dependency mapping, intelligent incident response orchestration, and closed-loop feedback mechanisms for continuous improvement. The proposed framework emphasizes the operationalization of reliability through measurable indicators such as service availability, mean time to detect, mean time to recover, and customer-impact metrics, aligned with strict service level agreements. A layered reliability governance model is introduced to coordinate network operations, DevOps, and vendor ecosystems, ensuring consistent reliability assurance across distributed cloud infrastructures. The framework also addresses scalability challenges, dynamic traffic behavior, and evolving threat landscapes by embedding adaptive capacity planning, stress testing, and fault-injection techniques into routine operations. By providing a structured and actionable reliability model tailored to 5G core networks, this study contributes a practical blueprint for telecom operators seeking to achieve sustained high availability at national and global scale. The framework supports not only technical robustness but also operational decision-making, enabling operators to proactively manage risk, reduce unplanned outages, and maintain service continuity in highly dynamic 5G environments. Overall, the proposed Operational Reliability Engineering Framework offers a comprehensive and scalable approach to sustaining high availability in mission-critical 5G core networks serving millions of users. The framework is intended to be technology-agnostic, interoperable with multivendor ecosystems, and applicable across standalone and non-standalone 5G deployments, supporting long-term network evolution while preserving operational stability, regulatory compliance, service assurance objectives, and continuous alignment with emerging industry standards and best practices worldwide today globally.