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A Joining Procedure and Synchronization for TSCH-RPL Wireless Sensor Networks

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Wireless Sensor Networks have become a key enabler for Industrial Internet of Things (IoT) applications; however, to adapt to the derived robust communication requirements, deterministic and scheduled medium access should be used, along with other features, such as channel hopping and frequency diversity. Implementing these mechanisms requires a correct synchronization of all devices in the network, a stage in deployment that can lead to non-operational networks. The present article presents an analysis of such situations and possible solutions, including the common current approaches and recommendations, and proposes a new beacon advertising method based on a specific Trickle Timer for the Medium Access Control (MAC) Time-Slotted Channel Hopping (TSCH) layer, decoupling from the timers in the network and routing layers. With this solution, improvements in connection success, time to join, and energy consumption can be obtained for the widely extended IEEE802.15.4e standard.
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... This involves the joining nodes as a cooperative part of the association process. Accordingly, an active scan procedure can accelerate the network formation without affecting the energy consumption of the joining nodes because broadcasting EBRs do not lead to additional energy consumption since nodes consume less energy in TX mode than in RX mode [9]. EBR, however, had never, to our knowledge, been used in the literature. ...
... Another beacon advertising method was proposed by Vera et al. in [9]. This solution aims to manage the EB sending interval by using a custom trickle timer. ...
Article
The Time Slotted Channel Hopping (TSCH) mode of the IEEE 802.15.4 standard is expected to revolutionize the Industrial Internet of Things. Indeed, it can achieve high reliability and deterministic latency with a very low duty cycle. Nevertheless, forming a TSCH network with the standard approach might not be as efficient, constituting, thus, one of the TSCH’s major issues. Such a network formation process relies on nodes passively scanning for advertised Enhanced Beacon (EB) frames to join the network. Doing so, a node wishing to join a TSCH network may stay awake randomly scanning for EBs for a considerable period of time, leading to a lengthy formation process with excessive energy consumption. To deal with these issues, this paper presents a practical and effective Radio duty-cycled, Active-Scan based network formation process for TSCH networks (RAST). Our proposal leans on active-scan procedures combined with radio duty cycling mechanisms to shorten joining delays and reduce energy consumption. Obtained results from extensive and realistic simulations show that our solution is efficient and outperforms state-of-the-art solutions, regarding the association time and energy consumption by up to two orders of magnitude.
... Very close to our contributions are the references [190], [191]. Through Cooja simulations, Vera-Pèrez et al. [190] investigate the optimal configuration of the TSCH and RPL parameters for improving the 6TiSCH network formation. ...
... Very close to our contributions are the references [190], [191]. Through Cooja simulations, Vera-Pèrez et al. [190] investigate the optimal configuration of the TSCH and RPL parameters for improving the 6TiSCH network formation. In particular, the authors suggest that nodes adopt a short period (i.e. 4 s) during the first two minutes of network advertising and then a longer period (i.e. ...
Thesis
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With current low-power wireless standards, the mistrust about wireless technology for industrial applications is unjustifiable. For instance, a Medium Access Control (MAC) technique, called Time Slotted Channel Hopping (TSCH), has made wire-like end-to-end reliability, certified security, and over a decade of battery lifetime a reality in Industrial Wireless Sensor Networks (IWSNs). TSCH is integrated into the IEEE~802.15.4 standard, and it is a cornerstone of the open standardised protocol suite for the Industrial Internet of Thing (IIoT) proposed by IETF. Specifically, the IETF 6TiSCH stack combines the industrial performance of TSCH with a set of higher layers protocols providing IPv6-connectivity to constrained devices. Thus, it promises, above all, interoperability between vendors and seamlessly integration of IWSNs into the Internet. Despite these high potentials and the high reputation of 6TiSCH in industry and academia, challenges remain, and some of its limitations need to be understood. In this thesis, we focus on the issues related to the harmonisation of the asynchronous IPv6-based upper layers with the synchronous TSCH technique,which rely on control plane primitives such as the network bootstrap procedure, the management of communication resources and the collection of network statistics. We identify in which circumstances the 6TiSCH standardised control primitives, which should lay the foundations for a reliable operational 6TiSCH network, exhibit limitations. After explaining the shortcomings and their causes, we design refinements and validate them simulatively. The focus is not on data transmissions but on mechanisms for a dependable exchanging of control messages. Nevertheless, these have been designed without significantly reducing the available bandwidth for data applications and the lifetime of power-constrained nodes. Accordingly, we provide the following main contributions. First, we analyse the interplay between the scheduling of control messages and the multi-hop route computation during the network bootstrap phase, pointing out the limits of the current guidelines that may preclude or penalise the 6TiSCH network's operational state. Indeed, an improper choice of the protocol parameters may lead to a very long and energy-consuming network formation and stabilisation phase (e.g. more than 30 minutes even in small 5x5 grid networks). Second, we examine different resource allocation strategies for bootstrapping a 6TiSCH network. Here, we design, implement and evaluate a scheduling mechanism for coordinating the transmission of control messages among neighbouring nodes in a dynamic and distributed way. This mechanism has exhibited a significantly faster network formation than the default configuration, even in challenging chain network topologies, where it consumes at most 0.4% of the battery's charge of a sensor node. Finally, we investigate how to obtain an accurate Link Quality Estimation (LQE) in 6TiSCH. We demonstrate that state-of-the-art strategies, which are not designed having TSCH in mind, are too inaccurate for guaranteeing a reliable and stable 6TiSCH network setup. Indeed, internal interference hampers their link measurements. To overcome this issue, we propose a LQE strategy that allows a collision-free transmission of broadcast probe messages even during the network setup. This proposal improves the estimation accuracy dramatically, exhibiting a quite perfect estimation of at least 90% of the links in different network topologies and in a short time (i.e. in order of minutes) We are firmly convinced that 6TiSCH is an IIoT key enabler. Despite that, we forewarn the risk of its blind adoption as one-size-fits-all solutions in this work. Addressing some limitations in its control primitives and providing essential enhancements, we believe this thesis supports the future wide adoption of 6TiSCH in the industry.
... That helps reduce the points of interference and path fading, thus increasing reliability. The problem here is that a large number of channels (N ch ) have a longer synchronization time [9]. ...
... In this scheduling shown in Fig. 2, 5 shared slots can be seen, 1 for each node (red). In addition, multiple inputs from the Mobile node (M) at different points of the slotframe (6,9,12; green) and a single arrival timeslot at the Sink node (11; yellow). Therefore, this solution uses 5 shared slots in a slotframe of 13. ...
Article
Full-text available
The growing use of mobile nodes in manufacturing environments is increasing the Quality of Service (QoS) requirements of the communications infrastructures that support them, as is the case with Industrial Wireless Sensor Networks (IWSN). Managing networks using Software Defined Networks (SDN) addresses the challenge of handling multiple sources in a satisfactory manner. The global vision of the topology that the SDN controller has allows a logical segmentation of the network, through the allocation of dedicated resources for each information flow, thus ensuring independent service levels and complete isolation. Mobile nodes produce constant changes in topology, which lead to instability for routing protocols. Traditional routing solutions with protocols such as Routing Protocol for Low-Power and Lossy Networks (RPL) require additional time to make the parent node change. This paper proposes Mobile Multicast Forwarding with Software Defined Network (MMF-SDN), an approach using Software Defined Networking solution for WIreless SEnsor Network (SDN WISE) protocol that exploits the advantages of SDN and Time Slotted Channel Hopping (TSCH) synchronism. The mobile nodes are managed as multicast sources, through a cumulative allocation of resources from the controller. This allows reception states to be synchronized at the parent nodes to provide network stability, avoiding subsequent recalculations in the routing protocol. Parent node changes are transparent and immediate. This proposal improves on other SDN based solutions, reducing energy consumption in reception by up to 50%, 70% end-to-end delay and improving scalability with a 30% reduction in slotframe occupancy.
... Implementing these techniques needs synchronization of all devices in the network. Thus, the authors in (Vera-Pérez et al., 2018) attempted to find a new beacon advertising mechanism depending on the trickle algorithm for the MAC TSCH layer and the timers in the network and network layers. The new solution combines IEEE802.15.4e with its TSCH modes and RPL. ...
Article
In the course of time, the Internet of Things (IoT) has attracted significant research interest. However, IoT devices have limited resources available in terms of battery power, processing capacity, memory, bandwidth, etc. In an attempt to provide connectivity and Internet Protocol version 6 (IPv6) support to IoT devices, the IPv6 routing protocol for Low-Power and Lossy Networks (RPL) was officially launched as the standard routing protocol for IoT in 2012. Despite being reputed and used in diverse applications, several recent studies have revealed RPL's drawbacks and limitations. The main objective of this work is to help the IoT research community understand all aspects of RPL. The paper also provides a detailed description of the operation of the RPL protocol. What is more, this work includes novel and thorough examples, thereby gaining practical knowledge of the pros and cons of this protocol. In addition, this paper reviews and summarizes relevant RPL-based protocols and conducts comprehensive comparisons among them from the perspectives of reliability, robustness, energy efficiency, and flexibility. Technically speaking, after studying and reviewing the majority of the proposed RPL solutions, we are ultimately capable, in this work, of highlighting all the challenges faced by IoT researchers while enhancing RPL and providing what is expected to be dealt with professionally. The present work also gives more details about RPL simulation platforms and RPL applications. Not only to this extent, but rather the historical bibliometric analysis of RPL, which shows the trends in the area of research to be focused on, has been professionally analyzed based on RPL challenges over the years 2010 and 2021. To this end, the conclusions and recommendations of this study are presented along with the effective directions for future RPL, and their applicability. As a result, the authors believe that this work will be a valuable reference for all RPL researchers and designers.
... Most of these solutions assume that all of the nodes are part of the network and have discovered the optimal routes to the sink. The algorithms related to EB scheduling are generally shared cell based solutions and they assume that nodes have only omni-directional antennas [24]. 6TiSCH minimal configuration is the standard strategy for the allocation of cells for the control frame transmission [21]. ...
Article
Full-text available
Steerable directional antennas are increasingly utilised to improve the overall performance of the traditional wireless sensor networks. Steerable directional antenna based networking solutions increase the network capacity by providing a longer range of transmission and reduced interference as compared to networking solutions with omni-directional antennas. However, the use of smart antennas requires complex algorithms and such algorithms may not be easily leveraged in low power Internet of Things (IoT) networks. This study presents mechanisms for integrating low complexity smart antenna solutions into IETF 6TiSCH protocol with the aim of creating scalable and reliable industrial IoT networks. The solution defines extensions to MAC layer and scheduling mechanisms of IETF 6TiSCH protocol to enable its seamless integration with low complexity steerable smart antennas. The results of this study show that smart antenna enabled 6TiSCH protocol stack outperforms the legacy 6TiSCH stack in terms of data delivery performance especially in high density scenarios.
... Most of these solutions assume that all of the nodes are part of the network and have discovered the optimal routes to the sink. The algorithms related to EB scheduling are generally shared cell based solutions and they assume that nodes have only omni-directional antennas [24]. 6TiSCH minimal configuration is the standard strategy for the allocation of cells for the control frame transmission [21]. ...
Preprint
Steerable directional antennas are increasingly utilised to improve the overall performance of the traditional wireless sensor networks. Steerable directional antenna based networking solutions increase the network capacity by providing a longer range of transmission and reduced interference as compared to networking solutions with omni-directional antennas. However, the use of smart antennas requires complex algorithms and such algorithms may not be easily leveraged in low power Internet of Things (IoT) networks. This study presents mechanisms for integrating low complexity smart antenna solutions into IETF 6TiSCH protocol with the aim of creating scalable and reliable industrial IoT networks. The solution defines extensions to MAC layer and scheduling mechanisms of IETF 6TiSCH protocol to enable its seamless integration with low complexity steerable smart antennas. The results of this study show that smart antenna enabled 6TiSCH protocol stack outperforms the legacy 6TiSCH stack in terms of data delivery performance especially in high density scenarios.<br
Article
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Emerging Industry 4.0 applications require ever-increasing amounts of data and new sources of information to more accurately characterize the different processes of a production line. Industrial Internet of Things (IIoT) technologies, and in particular Wireless Sensor Networks (WSNs), allow a large amount of data to be digitized at a low energy cost, thanks to their easy scalability and the creation of meshed networks to cover larger areas. In industry, data acquisition systems must meet certain reliability and robustness requirements, since other systems such as predictive maintenance or the digital twin, which represents a virtual mapping of the system with which to interact without the need to alter the actual installation, may depend on it. Thanks to the IEEE 802.15.4e standard and the use of Time-Slotted Channel Hopping (TSCH) as the medium access mechanism and IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) as the routing protocol, it is possible to deploy WSNs with high reliability, autonomy, and minimal need for re-configuration. One of the drawbacks of this communication architecture is the low efficiency of its deployment process, during which it may take a long time to synchronize and connect all the devices in a network. This paper proposes an analytical model to characterize the process for the creation of downstream routes in RPL, whose transmission of multi-hop messages can present complications in scenarios with a multitude of interfering nodes and resource allocation based on minimal IPv6 over the TSCH mode of IEEE 802.15.4e (6TiSCH). This type of multi-hop message exchange has a different behaviour than the multicast control messages exchanged during the synchronization phase and the formation of upstream routes, since the number of interfering nodes changes in each retransmission.
Conference Paper
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Synchronized communication has recently emerged as a prime option for low-power critical applications. Solutions such as Glossy or Time Slotted Channel Hopping (TSCH) have demonstrated end-to-end reliability upwards of 99.99%. In this context, the IETF Working Group 6TiSCH is currently standardizing the mechanisms to use TSCH in low-power IPv6 scenarios. This paper identifies a number of challenges when it comes to implementing the 6TiSCH stack. It shows how these challenges can be addressed with practical solutions for locking, queuing, scheduling and other aspects. With this implementation as an enabler, we present an experimental validation and comparison with state-of-the-art MAC protocols. We conduct fine-grained energy profiling, showing the impact of link-layer security on packet transmission. We evaluate distributed time synchronization in a 340-node testbed, and demonstrate that tight synchronization (hundreds of microseconds) can be achieved at very low cost (0.3% duty cycle, 0.008% channel utilization). We finally compare TSCH against traditional MAC layers: low-power listening (LPL) and CSMA, in terms of reliability, latency and energy. We show that with proper scheduling, TSCH achieves by far the highest reliability, and outperforms LPL in both energy and latency.
Article
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The IEEE 802.15.4e standard is an amendment of the IEEE 802.15.4-2011 protocol by introducing time-slotted channel hopping access behavior mode. However, the IEEE 802.15.4e only defines time-slotted channel hopping link-layer mechanisms without an investigation of network formation and communication scheduling which are still open issues to the research community. This article investigates the network formation issue of the IEEE 802.15.4e time-slotted channel hopping networks. In time-slotted channel hopping networks, a joining node normally takes a long time period to join the network because the node has to wait until there is at least one enhanced beacon message advertised by synchronized nodes (synchronizers) in the network on its own synchronization channel. This leads to a long joining delay and high energy consumption during the network formation phase, especially so in highly dynamic networks in which nodes join or rejoin frequently. To enable a rapid time-slotted channel hopping network formation, this article proposes a new design for slotframe structure and a novel adaptive joining scheme based on fuzzy logic. Our proposed scheme enables a synchronizer to be able to adaptively determine an appropriate number of enhanced beacons it should advertise, based on the number of available synchronizers in the network, so that joining nodes can achieve a short joining time while energy consumption of enhanced beacon advertisement at the synchronizers is optimized. Through extensive mathematical analysis and experimental results, we show that the proposed scheme achieves a significant improvement in terms of joining delay compared to state-of-the-art studies.
Article
Which wireless technology is able to meet the requirements of space launch vehicles in terms of latency, throughput and robustness? The IEEE 802.15.4e amendment has been designed to meet such requirements. More specifically, the Time Slotted Channel Hopping (TSCH) mode has been designed for industrial automation, process control and equipment monitoring. In this paper, we focus on the time needed by a joining node to detect beacons advertising the TSCH network. An Enhanced beacon is a TSCH frame that contains information on synchronization, channel hopping and timeslot used in the advertised network. However, the advertising policy is left unspecified by the IEEE 802.15.4e standard and is under the responsibility of a layer upper than the MAC one. Since beacons are broadcast, they are lost in case of collisions.The main problem is how to avoid such collisions? In this paper, we propose a Deterministic Beacon Advertising Algorithm, called DBA. The goal of DBA is to ensure that beacons are transmitted on all frequencies used by the TSCH network, regularly and without collision. With DBA, the exact value for the maximum time for a joining node to detect a beacon can be computed easily. We use the NS3 Simulator to evaluate this time as well as the number of message losses, considering different network topologies (star or multihop). We compare the performance of DBA with that of two algorithms existing in the state of the art.
Article
The industrial Internet of Things (IIoT) is expected to revolutionize the current industry. The capillary introduction of sensors and actuators for real-time monitoring and remote control and their seamless integration into existing information systems will represent a technological breakthrough. The definition of wireless communication standards will play a crucial role in reducing deployment costs and minimizing the time for installation. The new IPv6 over the TSCH mode of IEEE802.15.4e communication stack, 6TiSCH, represents the current leading standardization effort that aims at achieving both reliable and timed wireless communication and integration within IPv6 communication networks for industrial systems. In this paper, the network formation dynamics of 6TiSCH networks are assessed, considering the current guidelines for the so-called minimal configuration, a static initial configuration to guarantee control communication during network bootstrap. It is shown that the minimal configuration might lead to long network formation and suboptimal performance of the routing algorithm which may result into a disconnected network. In order to overcome this issue, a dynamic resource management algorithm to be executed during network bootstrap is proposed. Simulation and experimental results show that the proposed solution allows to minimize the network formation time and also helps in optimizing routing operations leading to the discovery of better routes.
Article
Time Slotted Channel Hopping (TSCH) Medium Access Control (MAC) is a key feature of the IEEE 802.15.4 standard, aimed at accommodating the requirements of industrial Internet of Things systems. Time Division Multiple Access (TDMA) is a main pillar of TSCH, on top of which frequency hopping is added to increase the resilience of short range radio links. A tight synchronization among the network nodes is required in TSCH. Luckily, once a node joins the network, several lean techniques can be used to keep alive its synchronization. On contrary, the subtleties of the joining phase in TSCH still deserve investigations since they could hinder an effective usage of the TSCH MAC. To this end, the problem of acquiring the first synchronization in a TSCH network is investigated hereby, from several perspectives: (i) four novel mechanisms are proposed and implemented in real motes to speed up joining operations; (ii) their average joining time is analytically modeled with closed form expressions as a function of node density, communication reliability, and beacon transmission frequency; (iii) their effectiveness and the agreement between experimental and theoretical outcomes are evaluated in several scenarios.
Conference Paper
Time Slotted Channel Hopping (TSCH) is one of main features of IEEE 802.15.4e standard designed for wireless sensor networks. It improves energy efficiency, network capacity and communication reliability in industrial applications. However, in the joining phase of TSCH network formation, sensor nodes have to remain awake status for a long time till they can reach synchronization. This is the reason which consumes a significant amount of energy. In this paper, we therefore propose a reliable lightweight joining scheme for TSCH network formation to speed up joining operation. The scheme is present in detail through analysis models as well as implementation result in real sensor nodes. Moreover, the comparison with other approaches is also mentioned to show the potential efficiency and better performance of our proposal.