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

On the (over)-Reactions and the Stability of a 6TiSCH Network in an Indoor Environment

International audienceIndustrial networks differ from others kinds of networks because they require real-time performance in order to meet strict requirements. With the rise of low-power wireless standards, the industrial applications have started to use wireless communications in order to reduce deployment and management costs. IEEE802.15.4-TSCH represents currently a promising standard relying on a strict schedule of the transmissions to provide strong guarantees. However, the radio environment still exhibits time-variable characteristics. Thus, the network has to provision sufficient resource (bandwidth) to cope with the worst case while still achieving high energy efficiency. The 6TiSCH IETF working group defines a stack to tune dynamically the TSCH schedule. In this paper, we analyze in depth the stability and the convergence of a 6TiSCH network in an indoor testbed. We identify the main causes of instabilities, and we propose solutions to address each of them. We show that our solutions improve significantly the stability

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

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