Image Processing Reference
In-Depth Information
need hundreds of them for realistic test conditions. Moreover, prototype hardware is very expensive
and far away from the targeted “ cent/node.” Consequently, a software environment is required that
combines the scaling power of simulations with real application behavior. Moreover, the administra-
tion of the network must not affect sensor network applications. Afterwards, three current software
approaches are presented.
12.4.1 A TinyOS SIMulator
Fault analysis of distributed sensor networks or their particular components is quite expensive and
time consuming especially when sensor networks consist of hundreds of nodes. For that purpose,
a simulator providing examination of several layers (e.g., communication layer, routing layer) is an
efficient tool for sensor application development.
TinyOS SIMulator (TOSSIM) is a simulator for wireless sensor networks based on the TinyOS
framework. As described in Refs. [,], the objectives of TOSSIM are scalability, completeness,
fidelity, and bridging. Scalability means TOSSIM's ability to handle large sensor networks with
many nodes in a wide range of configurations. The reactive nature of sensor networks requires
not only the simulation of algorithms but also the simulation of complete sensor network appli-
cations. Therefore, TOSSIM achieves completeness in covering as many system interactions as
possible. TOSSIM is able to simulate thousands of nodes running entire applications. The simu-
lator's fidelity becomes important for capturing subtle timing interactions on a sensor node and
between nodes. A significant attribute is the revealing of unanticipated events or interactions. here-
fore, TOSSIM simulates the TinyOS network stack down to bit level. At last, TOSSIM bridges the
gap between an academic algorithm simulation and a real sensor network implementation. There-
fore, TOSSIM provides testing and verification of application code that will run on real sensor
node hardware. his avoids programming algorithms and applications twice, for simulation and for
deployment. The TOSSIM components are integrated into the standard TinyOS compilation tool
chain which supports the direct compilation of unchanged TinyOS applications into the TOSSIM
framework.
Figure . shows a TinyOS application divided into hardware-independent and hardware-
dependent components. Depending on the target platform, the appropriate hardware-dependent
modules are selected in the compilation step. This permits an easy extension regarding new sensor
node platforms. At the same time, this is the interface to the TOSSIM framework. Compared with a
native sensor node platform, TOSSIM is a sensor node emulation platform supporting multiple sen-
sor node instances running on standard PC hardware. Additionally, the TOSSIM framework includes
a discrete event queue, a small number of reimplemented TinyOS hardware abstraction components,
mechanisms for extensible radio and analog-to-digital converter (ADC) models, and communication
services for external programs to interact with a simulation.
The core of the simulator is the event queue. Because TinyOS utilizes an event-based scheduling
approach, the simulator is event-driven, too. TOSSIM translates hardware interrupts into discrete
simulator events. The simulator event queue emits all events that drive the execution of a TinyOS
application. In contrast to real hardware interrupts, events cannot be preempted by other events and
therefore are not nested.
The hardware emulation of sensor node components is performed by replacing a small number
of TinyOS hardware components. hese include the ADC, the clock, the transmit strength variable
potentiometer, the EEPROM, the boot sequence component, and several components of the radio
stack. his enables simulations of a large number of sensor node configurations.
The communication services are the interface to PC applications driving, monitoring, and actuat-
ing simulations by communicating with TOSSIM over TCP/IP. The communication protocol was
designedatanabstractlevelandenablesdeveloperstowritetheirownsystemsthathookinto
TOSSIM. TinyViz is an example of a TOSSIM visualization tool that illustrates the possibilities
