Section: New Results


Self-adaptive MAC protocol for both QoS and energy efficiency in IoT

Participants : Shuguo Zhuo, François Despaux, Ye-Qiong Song [contact] .

The diversity of IoT applications implies the requirement of reliable yet efficient MAC solutions for supporting transmissions for various traffic patterns. We have mainly contributed to enhance the implementation of the high efficient traffic self-adaptive MAC protocols. As part of RIOT ADT project, our main achievements are the development of two MAC protocols lw-MAC and GoMacH [26]. lw-MAC is similar to X-MAC and ContikiMAC. It allows to introduce a first duty-cycled MAC into RIOT IoT protocol stack. GoMacH is a nearly optimal protocol that provides high reliability and throughput for handling various traffic loads in IoT. GoMacH seamlessly integrates several outstanding techniques. It adopts the phase-lock scheme to achieve low-power duty-cycled communication. It also utilizes a dynamic slots allocation scheme for providing accurate and instantaneous throughput boost. Furthermore, like in TSCH, GoMacH spreads its communications onto IEEE 802.15.4’s 16 channels, leading to high reliability. GoMacH has been implemented in open source on RIOT OS, and has also been seamlessly integrated into IETF’s 6LoWPAN/RPL/UDP stack as well as CCN-light. Experimental results on SAMR21-xpro test-beds and IoT-LAB verify the practicality of GoMacH and its capabilities for consistently providing high throughput, high delivery ratio, and low radio duty-cycle. They are both publically available on the RIOT open source github.

QoS and fault-tolerance in distributed real-time systems

Participants : Florian Greff, Laurent Ciarletta, Arnauld Samama [Thales TRT] , Dorin Maxim, Ye-Qiong Song [contact] .

The QoS must be guaranteed when dealing with real-time distributed systems interconnected by a network. Not only task schedulability in processors, but also message schedulability in networks should be analyzed for validating the system design. Fault-tolerance is another critical issue that one must take into account.

In collaboration with Thales TRT industrial partner as part of a CIFRE PhD work, we have developed a Software-Defined Real-time Network (SDRN) framework [14]. SDRN deals with the real-time flow allocation problem in mesh networks. The objective is to find a suitable path under delay constraint while allowing load balancing. For this purpose, combined online flow admission control and pathfinding algorithms have been developed on an SDN-like controller. At switch level, each output port is ruled by a credit-based weighted round robin, allowing isolation of flows. As a consequence, a freshly admitted flow will not influence existing flows, allowing incremental online admission of new flows. This approach has been applied to a RapidIO mesh network example and compared with the compositional performance analysis method. Numerical results clearly show the benefit of our proposal in terms of complexity and delay bound pessimism. In [15], Fault-tolerance issue in mesh networks has been addressed. In fact, one of the major advantages of a mesh topology is its ability to leverage the path redundancy in order to recover from link or node failures, through a flow reconfiguration process. However, one needs to ensure that hard real-time packets will keep being delivered on time during this transient reconfiguration period. Anticipating each possible fault is very complex and can result in a waste of network resource. Our contribution is the combination of an optimized content-centric source routing in nominal mode and a destination-tag flexible and scalable routing in transient recovery mode. We show the benefit of this approach in terms of flexibility and network resource utilization. Our method can ensure real-time properties enforcement even during the transient reconfiguration period. Algorithms have been developed to extend the SDRN flow allocation and routing methods in order to implement this hybrid fault-tolerant extension.

As part of Eurostars RETINA project, in the in-vehicle networking domain, we have focused on the evaluation of the worst-case response time of AVB traffic under time-aware shaper of TSN (time-sensitive networking). It is a hierarchical real-time scheduling problem, where a packet is scheduled by the credit-based shaper, priority and time-aware shaper (TDMA). We have proved that the eligible interval approach, developed for AVB, is still hold for TSN case. The worst case delay expression, as well as the feasibility condition are deduced. Our methods (analysis and simulation) are applied to an automotive use case, which is defined within the Eurostars RETINA project, and where both control data traffic and AVB traffic must be guaranteed. It has been shown that our delay bound is tight in single switch case [19].