Massive Internet-of-Things (IoT) deployments must simultaneously support monitoring, control, and safety-critical communication over shared wireless infrastructure. Classical timeliness metrics, such as Age of Information and its variants, quantify the freshness of received updates but do not account for deterministic safety timing requirements that arise in cyber-physical systems. Consequently, freshness-oriented metrics may indicate satisfactory performance even when worst-case timing guarantees required by functional safety standards are violated. This paper introduces the Unified Safety--Age Metric (USAM), a safety-aware timeliness metric that integrates information freshness, deadline reliability, and deterministic response-time feasibility into a single architecture-aware performance measure. We consider heterogeneous IoT traffic served by a gateway with intermittent receiver readiness and analyze system behavior in the ultra-sparse regime typical of massive machine-type communications. The analysis shows that, as device activity decreases, queueing delays become negligible and system timeliness becomes dominated by infrastructure readiness and deterministic response-time constraints. In this regime, feasibility is determined primarily by the receiver duty cycle rather than by average traffic load. Numerical results illustrate the safety-blindness of classical freshness metrics and demonstrate that USAM explicitly captures the feasibility boundary imposed by heterogeneous traffic requirements. The proposed framework provides a foundation for analyzing safety-aware communication architectures in large-scale IoT systems.

翻译：大规模物联网部署需在共享无线基础设施上同时支持监控、控制及安全关键通信。经典时效性度量指标（如信息年龄及其变体）量化了接收更新信息的新鲜度，但未考虑信息物理系统中由功能安全标准确定的确定性安全时序要求。因此，当违反功能安全标准所要求的极端情况时序保障时，以新鲜度为导向的指标仍可能显示性能达标。本文提出统一安全-年龄度量（USAM），这是一种安全感知的时效性度量指标，将信息新鲜度、截止时间可靠性及确定性响应时间可行性集成至单一架构感知的性能评价体系中。我们考虑由间歇性接收就绪网关服务的异构物联网流量，并分析大规模机器类通信典型超稀疏场景下的系统行为。分析表明，随着设备活动性降低，排队延迟可忽略，系统时效性由基础设施就绪度与确定性响应时间约束主导。在此场景下，可行性主要由接收器占空比而非平均流量负载决定。数值结果揭示了经典新鲜度指标的安全盲区，并证明USAM可显式捕获异构流量需求所施加的可行性边界。该框架为分析大规模物联网系统中的安全感知通信架构奠定了基础。