The 6TiSCH architecture is expected to play a significant role to enable the Internet of Things paradigm also in industrial environments, where reliability and timeliness are of paramount importance to support critical applications. Many research activities have focused on the Scheduling Function (SF) used for managing the allocation of communication resources in order to guarantee the application requirements. Two different approaches have mainly attracted the interest of researchers, namely distributed and autonomous scheduling. Although many different (both distributed and autonomous) SFs have been proposed and analyzed, a direct comparison of these two approaches is still missing. In this work, we compare some different SFs, using different behaviors in allocating resources, and investigate the pros and cons of using distributed or autonomous scheduling in four different scenarios, by means of both simulations and measurements in a real testbed. Based on our results, we also provide a number of guidelines to select the most appropriate SF, and its configuration parameters, depending on the specific use case. INDEX TERMS Industrial Internet of Things, 6TiSCH Architecture, Scheduling Function, Simulation and Measurements.

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Wireless Sensor Networks (WSNs) will represent a crucial enabling technology to interconnect sensors and actuators in future smart cities. Since many applications will demand for reliable and low-latency communication, current standardization efforts are focusing in the definition of novel wireless standard architectures, e.g., the 6TiSCH architecture, to improve reliability and introduce support for quality of service. In this paper, we evaluate the performance of the 6TiSCH architecture during the initial network formation. Specifically, the performance of the 6top protocol, defined in 6TiSCH for distributed negotiation of resources, is evaluated. Simulations highlighted how the initial negotiation of resources is influenced by the routing protocol and the link-quality estimation mechanism adopted. The performance evaluation allowed to draw a set of guidelines for network configuration to guarantee the reliability of the initial allocation of resources

The Time Slotted Channel Hopping (TSCH) ratified as an amendament to the IEEE 802.15.4 enables ultra low-power wireless communication among constrained devices, ensuring deterministic latency and high reliability. The IETF 6TiSCH Working Group (WG) is currently standardizing a novel Wireless Sensor Network (WSN) architecture to integrate networks of nodes adopting TSCH into existing IPv6 networks. Within the 6TiSCH architecture, a distribued algorithm, named Scheduling Function (SF), is assumed to be implemented on each node to manage the allocation of the communication resurces in a proper and efficient manner. Although many SFs have been proposed in literature, the WG is focusing on defining a reference SF named SF0, whose design is based on the original On-The-Fly (OTF) bandwidth reservation algorithm. In this paper, we carry out a performance evaluation of the OTF algorithm in order to evaluate if its current definition can ensure low latency data delivery with high reliability. In our evaluation, we focus on how its performance is influenced by the dynamics of the routing protocol and the 6top protocol, the protocol defined in the 6TiSCH architecure for the distributed negotiation of resources. Our results highlight that OTF performance is significantly influenced by the dinamicity of the routing protocol and by scheduling inconsistencies between neighbors that often lead to congestion from which the network hardly recover. In order to overcome such limitations, a modified version of the SF, named Enhanced-OTF, is proposed in order to mitigate the effects of congestion. The proposed approach is shown to effectively improve the overall network performance by allowing the nodes to recover from congestion in a short time.

The IETF is currently defining the 6TiSCH architecture for the Industrial Internet of Things to provide reliable and timely communication. 6TiSCH includes a distributed management mode, in which network resources are computed autonomously by nodes and allocated in a cooperative way. Specifically, nodes use the 6top protocol to negotiate network resources with their neighbors. In this paper, we investigate the performance of 6top protocol through a set of experimental measurements on a testbed. We show that the time required to complete a 6top transaction in a real environment is not negligible, as often assumed in many studies. In addition, a significant percentage of 6top transactions fails, with a negative impact the performance of the application. We investigate the reasons for such failures and propose some guidelines to reduce their number.