Image Processing Reference
In-Depth Information
depend on existing services at certain moments and when they are no longer available,
the nodes either reconfigure or try to provide them themselves.
•
Network structure
: New kinds of nodes may be added to the network. heir different and
increased capabilities will bring changes to the regular way in which the network func-
tions.Sotwaremodulesmightbeimprovedorcompletelynewsotwarefunctionality
might be implemented and deployed in the sensor nodes.
Most WSN architectures currently use a fixed layered structure for the protocol stack in each node.
This approach has certain disadvantages for WSNs. Some of them are:
•
Dynamic environment
: Sensor nodes address a dynamic environment where nodes have
to reconfigure themselves to adapt to the changes. Since resources are very limited,
reconfiguration is also needed in order to establish an efficient system (a totally new func-
tionality might have to be used if energy levels drop under certain values). he network
can adapt its functionality to a new situation, in order to lower the use of the scarce energy
and memory resources, while maintaining the integrity of its operation.
•
Error control
: It normally resides in all protocol layers so that for all layers the worst case
scenario is covered. For a WSN this redundancy might be too expensive. Adopting a cen-
tral view on how error control is performed and cross-layer design reduces the resources
spent for error control (and actually makes it feasible).
•
Power control
: It is traditionally done only at the physical layer, but since energy con-
sumption in sensor nodes is a major design constraint, it is found in all layers (physical,
data-link, network, transport, and application layer).
•
Protocol place in the sensor node architecture
:Anissueariseswhentryingtoplacecertain
layers in the protocol stack. Examples may include: timing and synchronization, local-
ization, and calibration. These protocols might shift their place in the protocol stack as
soon as their transient phase is over. The data produced by some of these algorithms
mightmakeadiferentprotocolstackmoresuitedforthesensornode(e.g.,alocalization
algorithm for static sensor networks might enable a better routing algorithm that uses
information about the location of the routed data destination).
•
Protocol availability
: New protocols might become available after the network deploy-
ment or at certain moments, in specific conditions, some of the sensor nodes might use
a different protocol stack that better suits their goal and the environment. The means
of changing or updating at run time parts of the software on the nodes is an important
needed feature.
4.3.2 Architecture Description
The system we are trying to model is an event-driven system, meaning that it reacts and processes the
incoming events and afterward, in the absence of these stimuli, it spends its time in the power-down
state (the software components running inside the sensor node are not allowed to perform blocking
waiting).
We introduce a higher level of abstraction for the event class as data. Data may encapsulate the
information provided by one or more events, have a unique name and contain additional infor-
mation such as time information, identity of producer, etc. Data is the means used by the internal
mechanisms of the architecture to exchange information components.
In the following we address any protocol or algorithm that can run inside a sensor node with
thetermentity(seeFigure..Anentityisasotwarecomponentthatwillbetriggeredbythe
availability of one or more data types. While running, each entity is allowed to read available data
types (but not wait for additional data types becoming available). As a result of the processing, each
