  Industrial Internet of Things (IIoT) technologies have revolutionized
industrial processes, enabling smart automation, real-time data analytics, and
improved operational efficiency across diverse industry sectors. IIoT testbeds
play a critical role in advancing IIoT research and development (R&D) to
provide controlled environments for technology evaluation before their
real-world deployment. In this article, we conduct a comprehensive literature
review on existing IIoT testbeds, aiming to identify benchmark performance,
research gaps and explore emerging trends in IIoT systems. We first review the
state-of-the-art resource management solutions proposed for IIoT applications.
We then categorize the reviewed testbeds according to their deployed
communication protocols (including TSN, IEEE 802.15.4, IEEE 802.11 and 5G) and
discuss the design and usage of each testbed. Driven by the knowledge gained
during this study, we present suggestions and good practices for researchers
and practitioners who are planning to design and develop IIoT testbeds for
connectivity research.
