DAG-Enabled blockchain and cloud-fog-IoT architecture for sustainable and secure smart City infrastructure

Smart city operations increasingly depend on timely and secure data management, yet Fog-IoT ecosystems face persistent issues related to latency, energy consumption, and data integrity. This study proposes a Cloud-Fog-IoT architecture integrated with a Directed Acyclic Graph (DAG)-based blockchain to enhance scalability and security. Experimental evaluation was conducted using a 10-node peer-to-peer topology (8:2 transaction mix of reads to writes, 1 MB block size, 500 ms block timeout) across Raspberry Pi 4B devices (4GB RAM, gigabit Ethernet). Compared to a cloud-IoT baseline (centralized AWS m5.large, mean network latency 70 ms) and a fog-only configuration (Intel NUC edge nodes, direct aggregation), the proposed system demonstrated a mean transaction throughput of 560 tx/s (95% CI: ), compared with 430 tx/s (95% CI: ) and 350 tx/s (95% CI: ), respectively. Mean end-to-end latency was reduced to 220 ms (95% CI: ), compared to 290 ms and 310 ms for cloud-IoT and fog-only systems. Energy consumption decreased to 0.22 Joules/tx (95% CI: [0.21, 0.23]), versus 0.37 and 0.30 Joules/tx for the baselines. The architecture supported 15 concurrent nodes versus 9 for the cloud-IoT system and achieved a transaction success rate of 99% (cloud-IoT: 90%; fog-only: 91%). Results indicate robust and scalable performance for secure smart city deployments, with consistent definitions and units throughout the manuscript.