Jacques Tiberghien

QoS-aware cross-layer mechanism for multiple instances RPL

In Low power and Lossy Networks (LNNs), routing has been considered as a main design and development challenge. This has led to the open design of the IPv6 routing protocol for LLNs called RPL. The protocol allows creating groups (instances) of multiple loop-free routing topologies over a physical network. The purpose of forming an optimized tree routing topology is to drive packets from the nodes to the collection point or sink which is the root of the tree. In this paper, we take advantage of extracted routing information to support high performance transmission of priority packets by proposing a QoS-aware cross-layer mechanism. The mechanism is explained and its performance is evaluated through simulation experiments. Simulation results show that the proposed mechanism provides high Packet Reception Ratio with low Packet Delivery Latency for priority traffic.

Poster Abstract: Outdoors Range Measurements with Zolertia Z1 Motes and Contiki

Practically useful outdoor transmission ranges have been determined experimentally for Zolertia Z1 motes running Contiki. Both internal and external antennas were tested. The analog and digital quality of the received signal as well as the packet delivery rate have been measured. The influence of transmission power, bushes and weather conditions have been explored. Internal antennas were excessively sensitive to orientation, while external antennas allowed reliable and rather stable communications over distances between motes of up to 150 m. Radio duty cycling was responsible for some, still partially unexplained, packet losses.

Demonstrating the Versatility of a Low Cost Measurement Testbed for Wireless Sensor Networks with a Case Study on Radio Duty Cycling Protocols

Today, Wireless Sensor Networks (WSNs) with open source operating systems still need many efforts to guarantee that the protocol stack succeeds in delivering its expected performance. This is due to subtle implementation problems and unexpected interactions between protocol layers. The subtleties are often related to the judicious choice of parameters, in particular those related to timing issues. As these issues are often not visible in simulation studies, this paper proposes a low-cost versatile measurement testbed and demonstrates its usefulness in measuring the performance of RDC protocols. We demonstrate how the testbed helped to identify bugs in the implementation of an RDC protocol.

How Interactions between RPL and Radio Duty Cycling Protocols Affect QoS in Wireless Sensor Networks

To guarantee that a Wireless Sensor Network succeeds in delivering its expected QoS, it is essential to understand and optimize cross-layer interactions. This paper presents a study on the interactions between the RPL routing protocol and Radio Duty Cycling (RDC) protocols. This study constitutes a first step towards a full understanding of their impact on the QoS of the network. By means of simulation and real world measurements, differences in the performance of RPL with different RDC protocols were observed and explained, and several properties of the RDC protocols impairing the performance of RPL were discovered.

An animated simulation environment for microprocessors

Abstract The dynamic observation of the state of a process while it executes is very helpful to give insight into the operation of a computer, and hints about causes of malfunction. Traditional teaching and debugging tools used to trace program execution give unfortunately very limited access to the state of a process by just displaying a few of the processor registers. An instruction set processor simulator build at the ‘Vrije Universiteit Brussel’ uses a multi-window users-interface to give its operator a more complete view of the state of the process that is executed on the simulated processor. This paper details the motivations for the project, its present status, and some of the technical aspects of its realization.

Tackling malfunctions caused by Radio Duty Cycling protocols that do not appear in simulation studies

When a commercial Wireless Sensor Network designed for environmental control and security in buildings was tested before being launched, disappointing differences between the behaviour in simulations and in the real world were observed. Fortunately, these differences disappeared when the energy saving radio duty cycling protocols were deactivated. The company then decided to provide their customers with larger batteries. They also suggested the authors of this paper to start an in depth experimental analysis of radio duty cycling as implemented in the Contiki operating system for Zolertia Z1 motes. Many subtle issues that remained hidden in simulations appeared to have infrequent but disruptive consequences in the real world. These issues have been identified, understood and corrected. They were a source of inspiration for recommendations tending to improve the overall reliability of Contiki.

Experimental Comparison of Radio Duty Cycling Protocols for Wireless Sensor Networks

The performances of three different asynchronous radio duty cycling protocols available in the Contiki lightweight operating system have been compared experimentally in view of their adoption in medium sized wireless sensor networks integrated in the Internet of Things. This study unveils some of the subtleties of those protocols, allowing an improved tuning of their parameters, as well as the identification of overlooked shortcomings and implementation flaws. To ensure fair comparisons default options have been unified and small implementation and design problems have been tackled. Besides the previously mentioned interventions, default values for parameters were kept. The results of the comparison can help designers of wireless sensor networks with their choices and guide designers of protocols to overcome some critical issues.

Experimental evaluation of message latency and power usage in WSNs

Different techniques for measuring packet delivery ratio, packet latency and power usage on single hop radio links have been developed. These techniques were tested with Zolertia Z1 motes running Contiki by measuring the performances of different radio duty cycling protocols using a range of radio wake-up rates and various levels of global radio traffic. Advantages and disadvantages of the different techniques are discussed and the feasibility of enhancing them for multihop networks is explored.

Distributed simulation of computer networks

Abstract Complexity and lack of adequate performance evaluation tools for computer networks make them analytically intractable and numerically prohibitive to evaluate. Simulation is therefore the only available evaluation method. Simulation of such complex networks is usually very slow. Using multiple processors appears to be a promising approach. In this paper, the applicability of different general purpose distributed simulation algorithms to the domain of computer network simulation is discussed. Several ways of introducing parallelism are discussed and evaluated.

Protocol description and simulation in the OCCAM programming language

Abstract Various high-level languages are being used to describe communication protocols and their implementations. This paper discusses the various considerations that have led the authors to the selection of Occam for this purpose.