A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations <s> E. Real Testbeds Evaluation <s> Wireless sensor networks are composed of large numbers of tiny networked devices that communicate untethered. For large scale networks, it is important to be able to download code into the network dynamically. We present Contiki, a lightweight operating system with support for dynamic loading and replacement of individual programs and services. Contiki is built around an event-driven kernel but provides optional preemptive multithreading that can be applied to individual processes. We show that dynamic loading and unloading is feasible in a resource constrained environment, while keeping the base system lightweight and compact. <s> BIB001 </s> A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations <s> E. Real Testbeds Evaluation <s> This paper introduces the FIT IoT-LAB testbed, an open testbed composed of 2728 low-power wireless nodes and 117 mobile robots available for experimenting with large-scale wireless IoT technologies, ranging from low-level protocols to advanced Internet services. IoT-LAB is built to accelerate the development of tomorrow's IoT technology by offering an accurate open-access and open-source multi-user scientific tool. The IoT-LAB testbed is deployed in 6 sites across France. Each site features different node and hardware capabilities, but all sites are interconnected and available through the same web portal, common REST interfaces and consistent CLI tools. The result is a heterogeneous testing environment, which covers a large spectrum of IoT use cases and applications. IoT-LAB is a one-of-a-kind facility, allowing anyone to test their solution at scale, experiment and fine-tune new networking concept. <s> BIB002
In this survey, we have reviewed and analyzed a significant number of proposals for RPL's enhancements that raises some observations regarding the use of testbeds evaluation in such proposals. An interesting observation is that only about 10% of reviewed articles have used real testbeds for the evaluation purposes. Even more interesting, the maximum number of nodes in such testbeds has never been greater than 30, a size only applicable to home automation applications. Simulation-based evaluation, while useful, cannot fully reflect all aspects of real scenarios. We argue therefore that research efforts to overcome the limitations of RPL should aim to evaluate solutions using real large-scale testbeds to reflect the settings in real-world environments. Such a large-scale open testbed for IoT research is available in BIB002 that provides an infrastructure populated with numerous IoT wireless sensor devices and heterogeneous communicating objects. Several IoT operating systems can be deployed on those nodes, including Contiki BIB001 and RIOT  [80].