M_PUBLISH: A Multi-Topic Publishing Protocol Extension for MQTT-Based IoT Systems

The Message Queuing Telemetry Transport (MQTT) protocol has become one of the most widely used messaging protocols for IoT and Industrial Internet of Things (IIoT) applications because of its lightweight publish–subscribe architecture. However, the standard MQTT PUBLISH message supports only a single topic–payload pair, requiring multiple protocol transactions and acknowledgment exchanges when several related measurements need to be transmitted together. This limitation increases communication overhead and latency, particularly in data-intensive IoT and IIoT environments. To address this limitation, this paper proposes M_PUBLISH, a protocol-level extension that aggregates multiple topic–payload pairs into a single MQTT control packet. At the broker, the aggregated packet is transparently decomposed into standard MQTT PUBLISH messages before being forwarded to subscribers, preserving native topic-based routing and compatibility with existing MQTT subscribers. The proposed protocol is analytically and experimentally evaluated in terms of latency, protocol overhead, frame size, and goodput across all MQTT QoS levels. The protocol is implemented in the aMQTT broker and validated under representative IoT/IIoT scenarios, including packet loss, network latency, bandwidth limitation, and selective subscribers. The results show up to 95% lower end-to-end latency, up to 20× higher goodput, and significantly lower protocol overhead while remaining compatible with existing MQTT subscribers and require modifications to publishers and brokers.