Niclas Finne

Cross-Level Sensor Network Simulation with COOJA

Simulators for wireless sensor networks are a valuable tool for system development. However, current simulators can only simulate a single level of a system at once. This makes system development and evolution difficult since developers cannot use the same simulator for both high-level algorithm development and low-level development such as device-driver implementations. We propose cross-level simulation, a novel type of wireless sensor network simulation that enables holistic simultaneous simulation at different levels. We present an implementation of such a simulator, COOJA, a simulator for the Contiki sensor node operating system. COOJA allows for simultaneous simulation at the network level, the operating system level, and the machine code instruction set level. With COOJA, we show the feasibility of the cross-level simulation approach

Run-time dynamic linking for reprogramming wireless sensor networks

From experience with wireless sensor networks it has become apparent that dynamic reprogramming of the sensor nodes is a useful feature. The resource constraints in terms of energy, memory, and processing power make sensor network reprogramming a challenging task. Many different mechanisms for reprogramming sensor nodes have been developed ranging from full image replacement to virtual machines.We have implemented an in-situ run-time dynamic linker and loader that use the standard ELF object file format. We show that run-time dynamic linking is an effective method for reprogramming even resource constrained wireless sensor nodes. To evaluate our dynamic linking mechanism we have implemented an application-specific virtual machine and a Java virtual machine and compare the energy cost of the different linking and execution models. We measure the energy consumption and execution time overhead on real hardware to quantify the energy costs for dynamic linkin.Our results suggest that while in general the overhead of a virtual machine is high, a combination of native code and virtual machine code provide good energy efficiency. Dynamic run-time linking can be used to update the native code, even in heterogeneous networks.

Making sensor networks IPv6 ready

With emerging IPv6-based standards such as 6LowPAN and ISA100a, full IPv6 sensor networks are the next major step. With millions of deployed embedded IPv6 devices, interoperability is of major importance, both within the sensor networks and between the sensors and the Internet hosts. We present uIPv6, the first IPv6 stack for memory-constrained devices that passes all Phase-1 IPv6 Ready certification tests. This is an important step for end-to-end interoperability between IPv6 sensors and any IPv6 capable device. To allow widespread community adoption, we release uIPv6 under a permissive open source license that allows both commercial and non-commercial use.

COOJA/MSPSim: interoperability testing for wireless sensor networks

Wireless sensor networks are moving towards emerging standards such as IP, ZigBee and WirelessHART which makes interoperability testing important. Interoperability testing is performed today through black-box testing with vendors physically meeting to test their equipment. Black-box testing can test interoperability but gives no detailed information of the internals in the nodes during the testing. Blackbox testing is required because existing simulators cannot simultaneously simulate sensor nodes with different firmware. For standards such as IP and WirelessHART, a white-box interoperability testing approach is desired, since it gives details on both performance and clues about why tests succeeded or failed. To allow white-box testing, we propose a simulation-based approach to interoperability testing, where the firmware from different vendors is run in the same simulator. We extend our MSPSim emulator and COOJA wireless sensor network simulator to support interoperable simulation of sensor nodes with firmware from different vendors. To demonstrate both cross-vendor interoperability and the benefits of white-box interoperability testing, we run the state-of-the-art Contiki and TinyOS operating systems in a single simulation. Because of the white-box testing, we can do performance measurement and power profiling over both operating systems.

TAC-03: a supply-chain trading competition

The Trading Agent Competition (TAC) has now become an annual fixture since its inception in 2000. The competition was conceived with the objective of studying automated trading strategies by focusing the research community on the development of competing solutions to a common trading scenario. The success of past TAC events has motivated broadening the scope of the competition beyond the context of the travel agent scenario used thus far. For the fourth edition of this competition, TAC-03, to be held in August 2003, the authors have created a novel supply-chain trading game with the aim of investigating automated agents in the context of dynamic supply-chain management.

The announcement layer: beacon coordination for the sensornet stack

Sensornet protocols periodically broadcast beacons for neighborhood information advertisement, but beacon transmissions are costly when power-saving radio duty cycling mechanisms are used. We show that piggybacking multiple beacons in a single transmission significantly reduces transmission costs and argue that this shows the need for a new layer in the sensornet stack--an announcement layer--that coordinates beacons across upper layer protocols. An announcement layer piggybacks beacons and coordinates their transmission so that the total number of transmissions is reduced. With an announcement layer, new or mobile nodes can quickly gather announcement information from all neighbors and all protocols by issuing an announcement pull operation. Likewise, protocols can quickly disseminate new announcement information to all neighbors by issuing an announcement push operation. We have implemented an announcement layer in the Contiki operating system and three data collection and dissemination protocols on top of the announcement layer. We show that beacon coordination both improves protocol performance and reduces power consumption.

Sensor Networking in Aquatic Environments - Experiences and New Challenges

In this paper we present the design and implemen tation of a small-scale marine sensor network. The network monitors the temperature in the Baltic Sea on different heights from the water surface down to the bottom. Unlike many other wireless sensor networks, this network contains both a wired and a wireless part. One of the major challenges is that the network is hard to access after its deployment and hence both hard- and software must be robust and reliable. We also present the design of an advanced buoy system featuring a diving unit that achieves a better vertical resolution and discuss remaining challenges of sensor networking in aquatic environments.

Integrating building automation systems and wireless sensor networks

Building automation systems (BAS) are used to control and improve indoor building climate at reduced costs. By integrating BAS with wireless sensor networks, the need for cabling can be removed, and both installation and operational costs significantly reduced. Furthermore, temporary BAS installations are made possible. By implementing and evaluating the open BAS standard BACnet on resource-constrained sensor nodes we show that integrating existing standard BAS protocols with wireless sensor networks is feasible.

Sensornet Checkpointing: Enabling Repeatability in Testbeds and Realism in Simulations

When developing sensor network applications, the shift from simulation to testbed causes application failures, resulting in additional time-consuming iterations between simulation and testbed. We propose transferring sensor network checkpoints between simulation and testbed to reduce the gap between simulation and testbed. Sensornet checkpointing combines the best of both simulation and testbeds: the non-intrusiveness and repeatability of simulation, and the realism of testbeds.

Accurate Network-Scale Power Profiling for Sensor Network Simulators

Power consumption is the most important metric in wireless sensor network research, but existing simulation tools for measuring or estimating power consumption are either impractical or have unclear accuracy. We present COOJA/MSPSim, a practical simulation-based tool for network-scale power estimation based on Contikis built-in power profiling mechanism, the COOJA sensor network simulator and the MSPSim sensor node emulator. We compare experimental results measured on real sensor nodes with simulation results for three different MAC protocols. The accuracy of our results indicates that COOJA/MSPSim enables accurate network-scale simulation of the power consumption of sensor networks.