Section: New Results

Quality-of-Service

Self-adaptive MAC protocol for both QoS and energy efficiency

Participants : Kévin Roussel, Shuguo Zhuo, Olivier Zendra, Ye-Qiong Song [contact] .

WSN research focus has progressively been moved from the energy issue to the QoS issue. Typical example is the MAC protocol design, which cares about not only low duty-cycle at light traffic, but also high throughput with self-adaptation to dynamic traffic bursts.

We have mainly contributed to enhancing the implementation of the high efficient traffic self-adaptive MAC protocols. As part of RIOT ADT project, we have improved and implemented a fully functional iQueue-MAC which provides not only the unique feature of high traffic self-adaptivity, but also the robustness by using two control channels (https://github.com/RIOT-OS/RIOT/pull/5618).

As part of LAR project, we were interested by using the Cooja/MSPSim network simulation framework for RIOT OS based platforms. We have showed that Cooja is not limited only to the simulation of the Contiki OS based systems and networks, but can also be extended to perform simulation experiments of other OS based platforms, especially that with RIOT OS. Moreover, when performing our own simulations with Cooja and MSPSim, we observed timing inconsistencies with identical experimentations made on actual hardware. Such inaccuracies clearly impair the use of the Cooja/MSPSim framework as a performance evaluation tool, at least for time-related performance parameters. The detailed results of our investigations on the inaccuracy problems, as well as the consequences of this issue, and possible ways to fix or avoid it are available in [27].

QoS and fault-tolerance in distributed real-time systems

Participants : Florian Greff, Laurent Ciarletta, Arnauld Samama [Thales TRT] , Eric Dujardin [Thales TRT] , 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 started a study on the real-time dependability of distributed multi-criticity systems interconnected by an embedded mesh network (RapidIO). For easing the QoS specification at the higher level, DDS middleware is used. We postulate that enhancing QoS for real-time applications entails the development of a cross-layer support of high-level requirements, thus requiring a deep knowledge of the underlying networks. This year, we proposed and implemented a new simulation/emulation/experimentation framework called ERICA, for designing such a feature. ERICA integrates both a network simulator (Ptolemy) and an actual hardware network to allow implementation and evaluation of different QoS-guaranteeing mechanisms. It also supports real-software-in-the-loop, i.e. running of real applications and middleware over these networks [21].

We have also dealt with mesh networking of embedded components. Our approach is to allow applications to make online real-time flow resource requests and consequently dynamically allot network resources according to these requirements. To this end, additional mechanisms must be provided in order to meet the real-time constraints while the platform remains as dynamic as possible. We gather these mechanisms into a Software-Defined Real-time Network (SDRN) paradigm. The online admission control and pathfinding algorithms have been developed allowing the controller to dynamically configure the real-time network nodes. We have evaluated several pathfinding algorithms.

Wireless sensor and actuator networks

Participants : Lei Mo, Adrian Guenard, Yifei Qi [Zhejiang University] , Jiming Chen [Zhejiang University] , Ye-Qiong Song [contact] .

Wireless sensor and actuator networks provide a key technology for fully interacting within a CPS (Cyber-Physical System). However, the introduction of the mobile actuator nodes in a network rises some new challenging issues. In this context, we addressed two important issues: the multiple target tracking using both fixed and mobile sensors and the optimal scheduling of mobile wireless energy chargers (actuators) for fixed sensor nodes.

In the low-cost and large-scale deployment of mobile sensor nodes for target tracking, due to the constraints of limited sensing range, it is of great importance to design node coordination mechanism for reliable tracking so that at least the target can always be detected with a high probability, while the total network energy cost can be reduced for longer network lifetime. In [3], we dealt with this problem considering both the unreliable wireless channel and the network energy constraint. We transfer the original problem into a dynamic coverage problem and decompose it into two subproblems. By exploiting the online estimate of target location, we first decide the locations where the mobile nodes should move into so that the reliable tracking can be guaranteed. Then, we assign different mobile nodes to each location in order that the total energy cost in terms of moving distance can be minimized. Extensive simulations under various system settings have shown the effectiveness of our solution.

We also investigated the multiple mobile chargers coordination problem that is minimizing the energy expenditure of the mobile chargers while guaranteeing the perpetual operation of the wireless sensor network. We extended our previous result (published in IPCCC2015) by taking into account mobile charger’s charging ability. We formulated this problem as a mixed-integer linear program (MILP), and proposed a novel decentralized method which is based on Benders decomposition. The convergence of proposed method is analyzed theoretically. Simulation results demonstrate the effectiveness and scalability of the proposed method.

NDN performance evaluation

Participants : Thibault Cholez [contact] , Xavier Marchal, Olivier Festor.

NDN (Named Data Networking) is a promising protocol that can help to reduce congestion at Internet scale by putting content at the center of communications instead of hosts. NDN can also natively authenticate transmitted content with a mechanism similar to website certificates that allows clients to assess the original provider. But this security feature comes at a high cost, as it relies heavily on asymmetric cryptography which affects server performance when NDN Data are generated. This is particularly critical for many services dealing with real-time data (VOIP, live streaming, etc.), but current tools are not adapted for a realistic server-side performance evaluation of NDN traffic generation when digital signature is used. We propose a new tool, NDNperf, to perform this evaluation and show that creating NDN packets is a major bottleneck of application performances. On our testbed, 14 server cores only generate $\sim$400 Mbps of new NDN Data with default packet settings. We gave recommendation about the configuration of NDN (packet size, cryptographic function) and proposed practical improvements to the NDN library that all combined can vastly increase the performance of server-side NDN Data generation (x8,5). This work was published in the ACM-ICN conference [22].