User's Manual

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Figure 14.
As described in the SmartMesh Network Overview section, devices in network spend the vast majority
of their time inactive in their lowest power state (doze). On a synchronous schedule a mote will wake to
communicate with another mote. Regularly occurring sequences which wake, perform a significant
function and return to sleep are considered atomic. These operations are considered atomic as the
sequence of events cannot be separated into smaller events while performing a useful function. For
example, transmission of a packet over the radio is an atomic operation. Atomic operations may be
characterized in either charge or energy. In a time slot where a mote successfully sends a packet, an
atomic transmit includes setup prior to sending the message, sending the message, receiving the
acknowledgment and the post processing needed as a result of the message being sent. Similarly in a
time slot when a mote successfully receives a packet, an atomic receive includes setup prior to listening,
listening until the start of the packet transition, receiving the packet, sending the acknowledge and the
post processing required due to the arrival of the packet.
To ensure reliability each mote in the network is provided multiple time slots for each packet it
nominally will send and forward. The time slots are assigned to communicate upstream with at least two
different motes. When combined with frequency hopping this provides temporal, special and spectral
redundancy. Given this approach a mote will often listen for a message that it will never receive, since
the time slot is not being used by the transmitting mote. It has already successfully transmitted the
packet. Since typically 3 time slots are scheduled for every 1 packet to be sent or forwarded, motes will
perform more of these atomic “idle listens” than atomic transmit or atomic receive sequences.
Examples of transmit, receive and idle listen atomic operations are shown below.