  The increased data transmission and number of devices involved in
communications among distributed systems make it challenging yet significantly
necessary to have an efficient and reliable networking middleware. In robotics
and autonomous systems, the wide application of ROS\,2 brings the possibility
of utilizing various networking middlewares together with DDS in ROS\,2 for
better communication among edge devices or between edge devices and the cloud.
However, there is a lack of comprehensive communication performance comparison
of integrating these networking middlewares with ROS\,2. In this study, we
provide a quantitative analysis for the communication performance of utilized
networking middlewares including MQTT and Zenoh alongside DDS in ROS\,2 among a
multiple host system. For a complete and reliable comparison, we calculate the
latency and throughput of these middlewares by sending distinct amounts and
types of data through different network setups including Ethernet, Wi-Fi, and
4G. To further extend the evaluation to real-world application scenarios, we
assess the drift error (the position changes) over time caused by these
networking middlewares with the robot moving in an identical square-shaped
path. Our results show that CycloneDDS performs better under Ethernet while
Zenoh performs better under Wi-Fi and 4G. In the actual robot test, the robot
moving trajectory drift error over time (96\,s) via Zenoh is the smallest. It
is worth noting we have a discussion of the CPU utilization of these networking
middlewares and the performance impact caused by enabling the security feature
in ROS\,2 at the end of the paper.
