Architectures for Wireless Sensor Networks - Networked Embedded Systems - page 55

phase. he node can exit the operation mode and passes through an initialization mode
if either the physical conditions around it or the conditions related to the network or
to itself changed. The operation mode is characterized by small bursts of node activity
(such as reading sensors values, performing computations, or participating in networking
protocols) and periods spent in an energy-saving low power mode.

4.2.1 Protocol Stack Approach
A first approach to building a wireless sensor network (WSN) is to use a layered protocol stack as a
starting point, as in the case of traditional computer network. he main difference between the two
kinds of networks is that the blocks needed to build the sensor network usually span themselves over
multiple layers while others depend on several protocol layers. his characteristic of sensor networks
comes from the fact that they have to provide functionality that is not present in traditional networks.
Figure . presents an example of mapping of the main blocks onto the traditional Open System
Interconnection (OSI) protocol layers.
The authors of Ref. [] propose an architecture based on the five OSI layers together with three
management planes that go throughout the whole protocol stack (see Figure .). A brief descrip-
tion of the layers included the physical layer addresses, mainly the hardware details of the wireless
communication mechanism (the modulation type, the transmission and receiving techniques, etc).
The data-link layer is concerned with the Media Access Control (MAC) protocol that manages com-
munication over the noisy shared channel. Routing the data between the nodes is managed by the
network layers, while the transport layer helps to maintain the data flow. Finally, the application layer
contains (very often) only one single-user application.
In addition to the five network layers, three management planes have the following functionality:
the power management plane coordinates the energy consumption inside the sensor node. It can, for
example, based on the available amount of energy, allow the node to take part in certain distributed
algorithms or to control the amount of traffic it wants to forward. he mobility management plane
manages all the information regarding the physical neighbors and their movement patterns as well as
its own moving pattern. he task management plane coordinates sensing in a certain region based on

Collaboration

Lookup Lookup

Application

Aggregation

Transport

Network

Routing

Cluster-

Clustering

Link

Physical

FIGURE . Relationship between building blocks/OSI layers.