Due to the flexibility it offers, publish–subscribe messaging middleware is a popular choice in Industrial IoT (IIoT) applications. The Data Distribution Service (DDS) is a widely used industry standard for these systems with a focus on versatility and extensibility, implemented by multiple vendors and present in myriad deployments across industries like aerospace, healthcare and industrial automation. However, many IoT scenarios require real-time capabilities for deployments with rigid timing, reliability and resource constraints, while publish–subscribe mechanisms currently rely on components that are not strictly real-time capable, such as the Linux networking stack, making it hard to provide robust performance guarantees without large safety margins. In order to make publish–subscribe approaches viable and efficient also in such real-time scenarios, we introduce user-space DDS networking transport extensions, allowing us to fast-track the communication hot path by bypassing the Linux kernel. For this purpose, we extend the best-performing vendor implementation from a previous study, CycloneDDS, to include modules for two widespread user-space networking technologies, the Data Plane Development Kit (DPDK) and the eXpress Data Path (XDP). Building on this, we additionally offer two more extensions to the second most performant implementation FastDDS, also based on DPDK and XDP, and realize novel optimizations not present in the original extension implementations. We evaluate each extension’s performance benefits against four existing DDS implementations (OpenDDS, RTI Connext, FastDDS and CycloneDDS). The DPDK-based and XDP-based extensions offer a performance benefit of 31%–38% and 18%–22% reduced mean latency, respectively, as well as an increase in bandwidth and sample rate throughput of at least 160%, while reducing the latency bound by at least 93%, demonstrating the performance and dependability advantages of circumventing the kernel for real-time communications.

Due to the flexibility it offers, publish-subscribe messaging middleware is a popular choice in Industrial IoT (IIoT) applications. The Data Distribution Service (DDS) is a widely used industry standard for these systems with a focus on versatility and extensibility, implemented by multiple vendors and present in myriad deployments across industries like aerospace, healthcare and industrial automation. However, many IoT scenarios require real-time capabilities for deployments with rigid timing, reliability and resource constraints, while publish-subscribe mechanisms currently rely on components that are not strictly real-time capable, such as the Linux networking stack, making it hard to provide robust performance guarantees without large safety margins. In order to make publish-subscribe approaches viable and efficient also in such real-time scenarios, we introduce userspace DDS networking transport extensions, allowing us to fasttrack the communication hot path by bypassing the Linux kernel. For this purpose, we extend the best-performing vendor implementation from a previous study, CycloneDDS, to include modules for two widespread user-space networking technologies, the Data Plane Development Kit (DPDK) and the eXpress Data Path (XDP), and we evaluate their performance benefits against four existing DDS implementations (OpenDDS, RTI Connext, FastDDS and CycloneDDS). The CycloneDDS-DPDK and CycloneDDS-XDP extensions offer a performance benefit of 31% and 18% reduced mean latency, respectively, as well as an increase in bandwidth and sample rate throughput of up to 59%, while reducing the latency bound by at least 94%, demonstrating the performance and dependability advantages of circumventing the kernel for real-time communications.

Publish-subscribe messaging is a popular communication paradigm in the (Industrial) Internet of Things, and the Data Distribution Service (DDS) is a well known standard for pub-sub communication middleware. Many vendor implementations of DDS exist, leaving users with the need to choose according to project and performance requirements. However, the wide range of parameters in DDS implementations not covered in the standard specification make this selection difficult and time-consuming. We present DDS-Perf, a novel and versatile cross-vendor benchmarking tool for performance analysis, and use it to provide data from studies on 4 popular DDS implementations (OpenDDS, RTI Connext, FastDDS and CycloneDDS) across a wide range of experimental setups. DDS-Perf allows us to provide a consistent methodology across all vendors, increasing fairness and comparability. Overall, we find that RTI Connext achieves the best all-round performance (exhibiting the best bandwidth and peak sample rate), while FastDDS (best end-to-end latency) and CycloneDDS also show promising results.

Publish-subscribe messaging has seen increased adoption in the context of timing critical applications, with multiple frameworks integrating publish-subscribe middleware into their ecosystem. The Data Distribution Service (DDS) is a standard for pub-sub systems that has gained traction, through e.g. the adoption in ROS2, with multiple vendors distributing their implementations of the standard. However, while DDS is being used in a real-time context, the examined implementations are not strictly real-time capable and therefore cannot provide hard timing guarantees to the application. Still, users are looking to take advantage of the flexibility offered by DDS in close-to real-time use cases, raising the question of how well DDS implementations can provide soft real-time reliability assurances. We use DDS-Perf, a novel cross-vendor benchmarking tool for impartial performance analysis of DDS implementations, to examine how reliably four vendors (OpenDDS, RTI Connext, Fast-DDS and CycloneDDS) can deliver real-time-like performance under different scenarios. From a typical out-of-the-box setup, we offer a guide to users for tuning performance/reliability and examine problems users might encounter trying to satisfy real-time constraints. The vendor implementations are tested against a range of experiments to evaluate operating performance under favorable and adverse conditions. Overall, we find that OpenDDS has the worst performance out-of-the-box and after calibration, while FastDDS and CycloneDDS offer the best performance, which is comparable to user-space networking technologies in the average case but with a much higher worst-case latency bound.