This work has been partially funded by the Spanish Ministry of Science, Innovation and Universities (ref. RTI2018-098156-B-C52), by the Research Plan of the University of Castilla-La Mancha (ref. 2019-GRIN-27060), and by FONDECYT / World Bank (ref. 026-2019 FONDECYT-BM-INC.INV).

Internet of Things (IoT) has posed new requirements to the underlying processing architecture, specially for real-time applications, such as event-detection services. Complex Event Processing (CEP) engines provide a powerful tool to implement these services. Fog computing has raised as a solution to support IoT real-time applications, in contrast to the Cloud-based approach. This work is aimed at analysing a CEP-based Fog architecture for real-time IoT applications that uses a publish-subscribe protocol. A testbed has been developed with low-cost and local resources to verify the suitability of CEP-engines to low-cost computing resources. To assess performance we have analysed the effectiveness and cost of the proposal in terms of latency and resource usage, respectively. Results show that the fog computing architecture reduces event-detection latencies up to 35%, while the available com...