User's Manual

1-8 Millennial Net
Introduction
Another critical design issue associated with periodic sampling applications is the phase relation
among multiple sensor nodes. If two sensor nodes operate with identical or similar sampling
rates, collisions between packets from the two nodes is likely to happen repeatedly. It is
essential that sensor nodes can detect this repeated collision and introduce a phase shift
between the two transmission sequences in order to avoid further collisions resulting in optimal
network operation and minimized power usage.
Event Driven
There are many cases that require monitoring one or more crucial variables immediately
following a specific event or condition. Common examples include fire alarms, door and
window sensors, or instruments that are user activated. To support event-driven operations
with adequate power efficiency and speed of response, the sensor node must be designed such
that its power consumption is minimal in the absence of any triggering event, and the wake-up
time is relatively short when the specific event or condition occurs. Many applications require a
combination of event driven data collection and periodic sampling.
Store and Forward
In many applications, data can be captured and stored or even processed by a sensor node
before it is transmitted to the gateway or base station. Instead of immediately transmitting
every data unit as it is acquired, aggregating and processing data by remote sensor nodes can
potentially improve overall network performance in both power consumption and bandwidth
efficiency. One example of a store-and-forward application is cold-chain management where
the temperature in a freight container carrying produce or pharmaceuticals, for instance, is
captured and stored; when the shipment is received, the temperature readings from the trip are
downloaded and viewed to ensure that the temperature and humidity stayed within the desired
range.
Bi-Directional Dialogue Data Models
Bi-directional dialogue data models are characterized by a need for two-way communication
between the sensor/actuator nodes and gateway/application. The MeshScape system supports
the bi-directional dialogue data models described in this section.
Polling
Controller-based applications, such as those found in building automation systems, use a
polling data model. In this model, there is an initial device discovery process that associates a
device ID with each physical device in the network. The controller then polls each device on the
network successively, typically by sending a serial query message and waiting for a response to
that message. For example, an energy management application would use a polling data model
to enable the application controllers to poll thermostats, variable air volume sensors, and other
devices for temperature and other readings.
On-Demand
The on-demand data model supports highly mobile nodes in the network where a gateway
device enters the network, automatically binds to that network and gathers data, then leaves
the network. With this model, one mobile gateway can bind to multiple networks and multiple
mobile gateways can bind to a given network. An example of an application using the