# Empirical Evaluation of TLS-Enhanced MQTT on IoT Devices for V2X Use Cases
## 2 Related Work
### Lightweight IoT Protocols and V2X  
At the application layer, CoAP and MQTT remain the most prevalent protocols for IoT communication due to their lightweight architecture [2; 18; 19]. CoAP, following a RESTful request-response model and operating over UDP, is designed for environments demanding low power consumption and reduced latency. MQTT, by contrast, uses a brokered publish/subscribe model over TCP/IP, which naturally supports asynchronous and decoupled communication. Table 1 summarizes key differences, showing that MQTT natively offers features such as reliability, Quality of Service (QoS) control, and decoupling between senders and receivers that counterbalance the advantages of CoAP [2]. Furthermore, its ability to handle larger payloads makes it highly suitable for dynamic vehicular networks, where complex or aggregated data need to be exchanged reliably. The literature confirms the suitability of MQTT across various domains. [PERSON] et al. [20] analyze broker performance on Raspberry Pi in smart city contexts, but their subscriber is a standard PC. [PERSON] et al. [21] conduct performance testing on constrained nodes but use a powerful broker machine (i7 computer with 2.4 GHz processor and 8 GB RAM). Similarly, [PERSON] et al. [22] evaluate MQTT in industrial IoT, running brokers in virtual machine (VM) environments. In contrast, our setup uses three Raspberry Pi 4 B boards as publisher, broker, and subscriber, representing full IoT deployment on uniform, mid-class hardware. [PERSON] et al. [23] explore security extensions such as Authentication and Authorization in Constrained Environments (ACE), showing feasibility on moderately constrained devices. However, these rely on authorization servers that do not reflect resource-constrained computing settings. Similarly, [PERSON] et al. [24] highlight how MQTT can support low-latency services within Industry 4.0 settings through its lightweight design. However, the authors use Cloud Servers, which are powerful in nature. In our work, we examine the use of MQTT in mid-power devices, such as Raspberry Pi 4\(B\), covering security issues of TLS, in full IoT deployment, where all the participants of the MQTT protocol are instances of IoT devices. [PERSON] [25] demonstrates that broker-based MQTT can lower end-to-end latency and improve horizontal scalability in connected vehicles, while [PERSON] et al. [26] present a generic MQTT interface that streams LiDAR detection from vehicles with sub-millisecond delays over 5G links. Both studies confirm MQTT's performance benefits for V2X, yet neither considers the confidentiality or authenticity of safety-critical payloads. [PERSON] and [PERSON] [27] take a first step toward secure messaging by proposing encrypted and authenticated MQTT dissemination of emergency alerts in Cellular V2X (C-V2X) networks, but they leave open the question of how such security measures affect resource-constrained vehicular hardware. More recent works further underscore MQTT's versatility in vehicular contexts. [PERSON] et al. [28] introduce the MIN-MQTT framework, which leverages network identifiers to enhance packet forwarding and mobility support in vehicular networks, adding data \begin{table}
\begin{tabular}{l c c} \hline \hline  & **CoAP** & **MQTT** \\ \hline Delay reduction & ✓ & \(\times\) \\ Minimized power consumption & ✓ & \(\times\) \\ Higher sleep time & ✓ & \(\times\) \\ Reliability & \(\times\) & ✓ \\ QoS flexibility & \(\times\) & ✓ \\ Congestion control & \(\times\) & ✓ \\ Client simplicity & \(\times\) & ✓ \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of CoAP and MQTT. integrity through signature verification, whereas [PERSON] et al. (2019) deploy an MQTT broker within an Advanced Driver Assistance System (ADAS) to enable real-time collision avoidance. [PERSON] et al. (2018) and [PERSON] et al. (2019) employ MQTT to protect vulnerable road users and manage intelligent intersections, respectively, both relying on road-side infrastructure and multiple high-end nodes.