# Publish/Subscribe-Middleware-Based Intelligent Transportation Systems: Applications and Challenges
## 4 Application of Publish/Subscribe Middleware in ITS  
This section explores middleware applications across different ITS domains, including infrastructure, where publish/subscribe architectures and distributed systems improve traffic monitoring; transportation modes, where middleware enhances maritime, land, and air transportation; and communication technologies, where advancements in mobile networks (4G/5G), P2P systems, and Information-Centric Networking (ICN) drive ITS efficiency. ITS can leverage middleware technologies to support real-time data dissemination, improve safety measures, and optimize transportation management, paving the way for next-generation smart mobility solutions.  
Figure 8 shows a functional taxonomy of publish/subscribe middleware applications in ITS that we extracted from the publication pool. The diagram categorizes middleware usage in ITS based on the transportation and computer networks paradigm. Our study found middleware applications in all modes of transportation. We also categorize the computer networking aspect of the applications based on the networking infrastructure types and communication technologies. The red boxes represent the main subsections of this section. The green boxes correspond to their respective subtopics, discussing each identified mode, infrastructure type, and communication technology in detail in the following subsections.  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Ref.** & **Middleware Name** & **FOSS** & **Developer-Stated Application Domain** \\ \hline
[33] & MQTT (Protocol) & \(\blacklozenge\) & Lightweight IoT messaging, embedded systems, telemetry \\
[34] & Apache Kafka & \(\blacklozenge\) & Distributed event streaming, big data pipelines, analytics \\
[35] & NATS & \(\blacklozenge\) & Cloud-native messaging, microservices, control systems \\
[36] & RabbitMQ & \(\blacklozenge\) & General-purpose messaging, enterprise integration, background jobs \\
[37] & ZeroMQ & \(\blacklozenge\) & Low-latency messaging for embedded, edge computing, and HPC \\
[38] & Apache Pulsar & \(\blacklozenge\) & Cloud-native streaming and messaging for data analytics \\
[31] & Google Cloud Pub/Sub & \(\blacklozenge\) & Cloud-native messaging and event ingestion \\
[39] & RTI Connect DDS & \(\blacklozenge\) & Safety-critical real-time systems: automotive, aerospace, robotics \\
[40] & OpenDDS & \(\blacklozenge\) & Real-time distributed systems: defense, automation \\
[41] & Fast DDS & \(\blacklozenge\) & Real-time robotics, autonomous vehicles, industrial systems \\
[42] & CoreDX DDS & \(\blacklozenge\) & Embedded real-time systems: avionics, defense, automotive \\
[43] & Vortex OpenSpilec & \(\blacklozenge\) & High-reliability embedded systems: marine, aerospace, SCADA \\
[44] & GurumDDS & \(\blacklozenge\) & Robotics, defense systems, autonomous platforms \\
[45] & Cyclone DDS & \(\blacklozenge\) & ROS2-based robotics, automation, distributed real-time applications \\ \hline \hline \end{tabular}
\end{table}
Table 4: Prominent publish/subscribe middleware solutions.  
Figure 8: Taxonomy of publish/subscribe middleware applications in ITS.