Analysis and Improvement of the On-The-Fly Bandwidth Reservation Algorithm for 6TiSCH

Abstract

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.

Analysis of Distributed and Autonomous Scheduling Functions for 6TiSCH Networks

“…In distributed scheduling [7]- [10], [20], nodes negotiate the allocation of TSCH cells with their neighbors, using the 6P protocol, and adapt the number of allocated cells, depending on traffic and network conditions. The communication schedule is typically non-optimal, however this approach is very suitable to large-scale and/or dynamic networks.…”

“…in managing congestion (e.g., originated by changes in the preferred parent). These limitations are overcome by E-OTF [7], [17], an enhanced version of OTF. The main drawback of distributed scheduling is the overhead due to 6P transactions.…”

“…In this paper, we compare three different SFs that take different approaches. Specifically, we consider ALICE [13] as autonomous SF, E-OTF [7] as fully distributed SF, and MSF [6] as hybrid SF, and analyze their performance in four different scenarios. Since ALICE is static (while E-OTF and MSF are adaptive to traffic changes), we also consider ALICE with the Frame Pending option enabled, which makes it adaptive to traffic changes.…”

“…In this paper, we consider three SFs for 6TiSCH that follow a different behavior for cell allocation. Specifically, we consider E-OTF [7], a completely distributed SF, ALICE [13] that leverages a link-based autonomous scheduling approach, and MSF [6] that combines both autonomous and distributed scheduling (MSF is currently under standardization by the 6TiSCH WG as the reference SF for IIoT applications). Both E-OTF and MSF are adaptive SFs, as they are able to adjust the number of allocated cells to time-varying traffic conditions, while ALICE leverages a static allocation policy and is, thus, unable to adapt to traffic changes.…”

On the suitability of 6TiSCH for industrial wireless communication

“…Another question related to this challenge is whether and to what extent the choice of RPL as routing protocol obstacles the adoption of the 6TiSCH-stack in industrial automation. From [Ri17] and [Ri18] it emerges that the interplay between 6top protocol and the dynamic of the RPL negatively affects the performance of the 6TiSCH-networks. We believe that the re-design of several mechanisms adopted by RPL (i.e.…”