Cryptography Reference
In-Depth Information
The processor unit contains the microprocessors which process information
received from the sensing unit. Due to energy constraints, the processing unit performs
partial processing of data and leaves the extensive processing to the sink node. Hence
the processors operate in different modes, so that they can lower their activity in situa-
tions of lower battery power. However, the decision to change to a different processing
mode requires collaboration with other layers. (Layered architecture is discussed in
Section 1.5).
Operating frequency and operating voltage determine the amount of energy
required by the microprocessor. New voltage scheduling schemes have been adopted to
save energy (dynamic voltage scheduling), which take operating voltage and frequency
into consideration during processing (Pillai and Shin 2001). Recent research has shown
that the amount of energy required by the communication unit is much greater than
that of the processing unit.
The communication unit consists of a short-range transceiver, customized to
operate in a resource-constrained environment. The limited battery energy forces
the transceiver to adopt a hop-by-hop mechanism over the end-to-end mechanism
adopted by legacy IP networks. For this reason, sensor nodes are placed in close prox-
imity to each other, so that the node discovery phase and routing process consume less
battery power.
1.5 The Protocol Stack in WSN
WSN operate in a resource-constrained environment and therefore deviate from the
traditional Open System Interconnection (OSI) model. A WSN stack is usually com-
prised of six layers: an application layer, middleware, transport, network, data link,
and a physical layer. In addition to these six layers that are mapped to each sensor
node, there are three more planes that span across the entire sensor network and
have more visibility to address issues such as mobility, power, and task management
(Figure 1.6).
Application layer: The application layer aims to create an abstraction of the main
functions of the sensing application, thereby making the lower software and
hardware levels transparent to the end user. The application layer involves sev-
eral processes running simultaneously, and handles user requests relating to data
aggregation, location finding, sleep/awake cycle control, time synchronization,
authentication, encryption, key distribution, and other security measures. It also
defines the order and format of message exchange between the two communica-
tion parties.
Middleware: The middle layer provides an Application Program Interface (API)
for applications existing in the upper layers, and may involve complex function-
alities such as resource sharing and task management.
Transport layer: The transport layer is responsible for flow and congestion control.
It also performs error control to detect corrupted frames that arrive from lower
layers. Due to the severe operating environment and lesser transmission power,
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