Is Link-Layer Anycast Scheduling Relevant for IEEE802.15.4-TSCH Networks?

International audienceWith the wide adoption of low-power wireless transmissions , industrial networks have started to incorporate wireless devices in their communication infrastructure. Specifically, IEEE802.15.4-TSCH enables slow channel hopping to increase the robustness, and relies on a strict schedule of the transmissions to increase the energy efficiency. Anycast is a link-layer technique to improve the reliability when using lossy links. Several receivers are associated to a single transmission. That way, a transmission is considered erroneous when none of the receivers was able to decode and acknowledge it. Appropriately exploited by the routing layer, we can also increase the fault-tolerance. However, most of the anycast schemes have been evaluated by simulations, for a sake of simplicity. Besides, most evaluation models assume that packet drops are independent events, which may not be the case for packet drops due to e.g. external interference. Here, we use a large dataset obtained through an indoor testbed to assess the gain of using anycast in real conditions. We also propose a strategy to select the set of forwarding nodes: they must increase the reliability by providing the most independent packet losses. We demonstrate using our experimental dataset that anycast improves really the performance, but only when respecting a set of rules to select the next hops in the routing layer

A distributed algorithm for semantic collectors election in wireless sensors networks

Semantic clustering is a recent technique for saving energy in wireless sensor networks. Its mechanism of action consists in dividing the network into groups (clusters) formed by semantically related nodes and at least one semantic collector, which acts as a bridge between its internal nodes and the sink node. Since semantic collector nodes need to perform more tasks than normal nodes, they deplete their energy budget faster, so it is necessary to use efficient mechanisms for electing semantic collectors to prolong the network lifetime. Our hypothesis is that an effective choice of semantic collectors allows a longer network lifetime. To test it, we start from a previous work of the authors of this article and we propose an algorithm for electing semantic collectors in a distributed way based on a fuzzy inference engine. The inputs of the inference engine are the residual energy of nodes and their received signal strength indicator (RSSI). Simulation results confirm our hypothesis, since the algorithm provides (i) an improvement of 17.4% in relation to another proposal of the related literature, and (ii) a gain of 68.8% over the time life of the network’s original work.Keywords: Wireless Sensors Networks, Semantic Cluster, Semantic Collector Election

Améliorations des normes pour la performances prévisibles dans l'Internet des objets industriel dans les ambiances à l’intérieur

Les réseaux industriels sont utilisés pour surveiller les processus liés à la sécurité, où une fiabilité élevée et des délais prévisibles doivent être assurés. Pour cette raison, la norme IEEE 802.15.4-2015 a été publiée en 2016, en définissant le mode TSCH (Time-Slotted Channel Hopping). TSCH permet l’ordonnancement des transmissions où chaque noeud dispose de ressources dédiées pour communiquer en évitant les collisions. De plus, le mécanisme de saut de canal permet aux noeuds d’atténuer les effets des interférences externes. Toutefois, les pertes de paquets continuent à se produire en raison de variations de radio. L’objectif de ce travail est d’améliorer la fiabilité des réseaux sans fil dans les environnements intérieurs, où les obstacles et les interférences externes sont la règle. Nous nous concentrons principalement sur la recherche expérimentale pour identifier les limites et dans quelles circonstances ces réseaux ne parviennent pas à fournir une performance prévisible.Industrial networks are typically used to monitor safety-related processes, where high reliability and an upper-bounded delay must be ensured. To attend these requirements, IEEE 802.15.4-2015 standard was published in 2016, defining the Time-Slotted Channel Hopping (TSCH) mode. TSCH allows the scheduling of transmissions, such that each device has enough opportunities for communicating while avoiding collisions. In addition, slow-channel hopping mechanism allows the nodes to combat the effect of external interference. Although TSCH increases the reliability, packet losses keep on occurring due to variations on the radioconditions, very common in indoor environments. The goal of this work is to improve the reliability of low-power wireless networks in indoor scenarios, where obstacles and external interference are the rule. We focus mostly on experimental research to identify the limits and in which circumstances these networks fail at providing a predictable performance

Modeling Wireless Sensor Network Lifetime Using Survival Analysis

CoordenaÃÃo de AperfeiÃoamento de NÃvel SuperiorAs Redes de Sensores Sem Fio (RSSF) sÃo exemplos de Resource-Constrained Networks (RCNs) nas quais recursos de processamento, armazenamento e energia sÃo limitados. A partir do momento em que uma RSSF tÃpica entra em funcionamento, decorre-se um intervalo de tempo, conhecido como tempo de vida da rede, durante o qual os nÃs sensores executam operaÃÃes de sensoriamento, processamento e comunicaÃÃo, consumindo energia de suas fontes (e.g. pilhas) atà valores mÃnimos de carga que os mantÃm em operaÃÃo. Estimar a priori a estrutura probabilÃstica/estocÃstica do tempo de vida de uma RSSF antes da sua implantaÃÃo fornece meios de elaborar estratÃgias de manutenÃÃo de forma a maximizar seu tempo de vida e de garantir que a rede sobreviverà tempo suficiente para cumprir seu objetivo. Assim sendo, esta dissertaÃÃo aborda os modelos Exponencial, Weibull e Log-Normal, comumente utilizados em estudos de AnÃlise de SobrevivÃncia, para obter estimativas do tempo de sobrevivÃncia de uma rede real a partir dos tempos de vida de seus nÃs observados em simulaÃÃo. Nossa hipÃtese de base à a de que a AnÃlise de SobrevivÃncia pode melhorar a acurÃcia da estimativa do tempo de vida de uma RSSF e, por conseguinte, o seu planejamento operacional. Aqui propomos respostas a trÃs questÃes em aberto na literatura: (i) quantos nÃs sensores irÃo sair de operaÃÃo durante o tempo de vida de uma RSSF (ii) em qual intervalo de tempo a maior parte dos nÃs vai sair de operaÃÃo (iii) por quanto tempo a rede permanecerà em funcionamento.Wireless Sensor Networks (WSN) are examples of Resource-Constrained Networks (RCNs) in which processing resources, storage and energy are limited. From the moment a typical WSN goes into operation, the sensor nodes begin to perform operations like sensing, processing and communicating, consuming the stored energy in their batteries until its ends completely, a situation that is characterized like the death of the devices and consequently the network. Knowing a priori the expected lifetime of a WSN before deploying it, enables the development of maintenance strategies to maximize it lifespan and ensure that it survives enough time to accomplish it goal. Therefore, we propose in this work the use of Exponential, Weibull and Log-Normal models, which are commonly used in studies of Survival Analysis, to infer survival statistics of a real network from the lifespans of its nodes observed in simulation. Our hypothesis is that the Survival Analysis may improve the accuracy of estimating the lifetime of a WSN and, consequently, their operational planning. This work proposes answers to three questions which are open in the literature: (i) how many sensor nodes will die during the lifetime of a WSN (ii) in which time period most of the nodes will die (iii) for how long network will remains operational

Améliorations des normes pour la performances prévisibles dans l'Internet des objets industriel dans les ambiances à l’intérieur

Industrial networks are typically used to monitor safety-related processes, where high reliability and an upper-bounded delay must be ensured. To attend these requirements, IEEE 802.15.4-2015 standard was published in 2016, defining the Time-Slotted Channel Hopping (TSCH) mode. TSCH allows the scheduling of transmissions, such that each device has enough opportunities for communicating while avoiding collisions. In addition, slow-channel hopping mechanism allows the nodes to combat the effect of external interference. Although TSCH increases the reliability, packet losses keep on occurring due to variations on the radioconditions, very common in indoor environments. The goal of this work is to improve the reliability of low-power wireless networks in indoor scenarios, where obstacles and external interference are the rule. We focus mostly on experimental research to identify the limits and in which circumstances these networks fail at providing a predictable performance.Les réseaux industriels sont utilisés pour surveiller les processus liés à la sécurité, où une fiabilité élevée et des délais prévisibles doivent être assurés. Pour cette raison, la norme IEEE 802.15.4-2015 a été publiée en 2016, en définissant le mode TSCH (Time-Slotted Channel Hopping). TSCH permet l’ordonnancement des transmissions où chaque noeud dispose de ressources dédiées pour communiquer en évitant les collisions. De plus, le mécanisme de saut de canal permet aux noeuds d’atténuer les effets des interférences externes. Toutefois, les pertes de paquets continuent à se produire en raison de variations de radio. L’objectif de ce travail est d’améliorer la fiabilité des réseaux sans fil dans les environnements intérieurs, où les obstacles et les interférences externes sont la règle. Nous nous concentrons principalement sur la recherche expérimentale pour identifier les limites et dans quelles circonstances ces réseaux ne parviennent pas à fournir une performance prévisible

Impact of the Initial Preferred Parent Choice in Wireless Industrial Low-Power Networks

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Experimental in-depth study of the dynamics of an indoor industrial low power lossy network

International audienceAn increasing number of industrial applications rely on low power embedded devices because of their flexibility. To work properly, the network has to respect requirements concerning specifically the delay and the reliability. Fortunately, low power, and slow channel hopping MAC help to cope with these requirements. For instance, IEEE802.15.4-TSCH relies on a strict schedule of the transmissions, spread over orthogonal radio channels, to setup a resilient wireless infrastructure. A routing protocol (e.g. RPL) has then to construct energy-efficient routes on top of this link-layer topology. Unfortunately, the radio environment keeps on exhibiting time-varying characteristics, due to e.g. obstacles, and external interference. In a reservation-based stack, the network will have to implement over-provisioning, to cope with small-term variations: additional resources allow the network to operate in the worst situation. Inversely, long-term changes are triggered only when a node/link failure is detected. In this paper, we investigate experimentally the performance stability of a 6TiSCH/ IETF/ RPL stack in collocated deployments. We focus on some key metrics to exhibit the intermittent losses of guarantees (e.g. delivery ratio) under yet static conditions. Our results in large scale testbeds highlight that in the presence of radio oscillations, 6TiSCH introduces frequent network reconfigurations to combat interference and provide high reliability. We perform a multi-layer analysis of the 6TiSCH stack identifying the main sources of instability and proposing solutions to address each one of them. Our performance evaluation highlights the accuracy of our solutions to set up an efficient and reliable network

Passive Link Quality Estimation for Accurate and Stable Parent Selection in Dense 6TiSCH Networks

International audienceIndustrial applications are increasingly demanding more low-power operations, deterministic communications and end-to-end reliability that approaches 100%. By keeping nodes time-synchronized and by employing a channel hop- ping approach, IEEE 802.15.4-TSCH (Time-Slotted Channel Hoping) aims at providing high-level network reliability. For this, however, we need to construct an accurate schedule, able to exploit reliable paths. In particular, radio links with high Packet Error Rate should not be exploited since they are less energy-efficient (more retransmissions are required) and they negatively impact the reliability. In this work, we take advantage of the continuously advertisement packets transmitted by the nodes to identify neighbors with a good link quality. We argue that when a node ranks its neighbors through their rate of broadcast packets received, it can identify stable parents, even when the data packets use different, collision-free transmission opportunities. Our experiments on a large-scale platform highlight that our approach improves the convergence delay, identifying the best routes to the border router during the bootstrapping (or re- converging) phase without adding any extra control packet

Scheduling for IEEE802.15.4-TSCH and Slow Channel Hopping MAC in Low Power Industrial Wireless Networks: A Survey

International audienceThe so-called Industrial Internet of Things (IIoT) is expected to transform our world, and in depth modernize very different domains such as manufacturing, energy, agriculture, construction industry, and other industrial sectors. The need for low power radio networks first led to low duty cycle approaches where nodes turn off their radio chipset most of the time to save energy. The medium access control (MAC) has thus been largely investigated over the last fifteen years. Unfortunately, classical contention access methods use a random access and are unable to provide guarantees. In the meantime, some dedicated standards have emerged (e.g. IEEE 802.15.4-2006, IEEE 802.15.4-2015), combining Time Division Multiple Access (TDMA) with slow channel hopping in order to enable reliability and energy efficiency. Slow channel hopping allows each node to use different channels for a frame and its possible retransmissions with a low-cost hardware. To provide high-reliability, these protocols rely on a common schedule in order to prevent simultaneously interfering transmissions. In this context, we clearly observe a strong growth of the number of proposals in the last years, denoting a strong interest of the research community for deterministic slow channel hopping scheduling for the IIoT. We categorize here the numerous existing solutions according to their objectives (e.g. high-reliability, mobility support) and approaches. We also identify some open challenges, expected to attract much attention over the next few years

Analysis of the Network Attachment Delay of Mobile Devices in the Industrial Internet of Things

International audienceIndustrial networks are typically used to monitor safety-related processes where high reliability and an upper bounded latency are crucial. Because of its flexibility, wireless is more and more popular, even for real-time applications. Because radio transmissions are known to be lossy, deterministic protocols have been proposed, to schedule carefully the transmissions to avoid collisions. In parallel, industrial environments now integrate mobile industrial robots to enable the Industry 4.0. Thus, the challenge consists in handling a set of mobile devices inside a static wireless network infrastructure. A mobile robot has to join the network before being able to communicate. Here, we analyze this attachment delay, comprising both the synchronization, and the negotiation of dedicated cells. In particular, since the control frames (EB and 6P) have a strong impact on the convergence, our proposed model carefully integrates the collision probability of these packets. We validate the accuracy of our model, and we analyze the impact of the different EB transmission policies on the discovery delay. Our performance evaluation demonstrates the interest of using efficiently the radio resources for beacons to handle these mobiles devices