# Empirical Evaluation of TLS-Enhanced MQTT on IoT Devices for V2X Use Cases
## 3 MQTT and V2X Use Cases
It is important to mention that the message requirements will depend on the type of emergency. That is to say, within the message payload, the alert message varies, where it can symbolize any type of emergency alert, from an object on the road to an accident requiring immediate intervention. In such latency-sensitive contexts, maintaining message authenticity, integrity, and confidentiality is critical to preventing spoofing, false signal injection, or data leakage. In V2V (Vehicle-to-Vehicle) communication, MQTT facilitates peer-level data exchange. Each vehicle may simultaneously act as a publisher and a subscriber, sharing and con  
Figure 2: Examples of MQTT message exchange in V2X scenarios. suming information on proximity-based topics through an MQTT broker, which could be an in-network unit like an RSU or even a vehicle acting in a temporary broker role. This setup supports coordinated actions like synchronized driving, where consistent and trusted communication is essential [25]. In structured V2V paradigms like platooning [35; 36], multiple vehicles coordinate their movements in real time, which can include merging, lane changes, intersection crossing, or cooperative adaptive cruise control. Each vehicle may transmit telemetry, speed, and braking status as a publisher while also subscribing to others' data. A designated lead vehicle can operate as the MQTT broker, managing message flow and maintaining group coherence. Vehicles adjust their behavior based on this broker-managed data stream whose integrity is essential. All participating nodes must be authenticated and messages must be signed and encrypted to ensure origin authenticity and integrity. In V2N use cases, MQTT enables long-range communication over cellular or 5G networks. For example, RSUs can operate as publishers, transmitting congestion data, traffic incidents, or routing recommendations. These are relayed through a centralized cloud-based MQTT broker, to which vehicles subscribe dynamically based on their geographic location [37]. The same architecture supports upstream data flows, where vehicles act as publishers, continuously streaming telemetry (e.g., engine diagnostics, sensor payloads, or driving behavior metrics) to the cloud. Cloud-based services act as subscribers, consuming this information through the broker to enable functions such as monitoring or predictive maintenance [38]. To maintain trust in such environments, information dissemination plays a pivotal role. Robust identity management is necessary, data consistency must be preserved in transmission, and private diagnostics should not be exposed beyond authorized systems. V2P scenarios provide another example of the usefulness of MQTT in safety-critical, low-latency interactions. LiDAR or vision-based sensors installed near crosswalks or urban corners act as publishers, broadcasting pedestrian detection events on predefined MQTT topics. These alerts are routed through an MQTT broker, typically deployed on edge computing elements co-located with RSUs. Vehicles entering the sensor coverage zone operate as subscribers, receiving real-time pedestrian presence updates through the broker [25]. Given the time-sensitive and safety-critical nature of V2P interactions, the MQTT communication framework must enforce strict publisher authentication, ensuring that only certified sensor nodes are allowed to publish, messages are not be modified during their transmission, and personal information is adequately protected from third-party access. Figure 2 provides an illustrative representation of V2X communication enabled by MQTT, demonstrating the simultaneous operation of V2I, V2V, V2N, and V2P scenarios within a unified, event-driven messaging architecture. The lightweight MQTT publish/subscribe paradigm facilitates asynchronous data exchange across vehicular and infrastructure nodes.