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In-Motes: Network Topology
The facilitator agent
works by continuously checking whether any of the nodes are available for
capture. The capturing procedure takes places when a facilitator agent during
its migration registers a capture or a slave reaction to the analogous node. A
counter will be incremented every time a capture reaction takes place; here we
restrict the registration of two agents under each facilitator purely based on
the motes we had available. When the counter reaches two, the facilitator agent
will migrate again to the next available node assigning this time around a new
facilitator tuple and slave reaction and the capturing procedure will repeat.
Therefore the federated system communication model will be established covering
all the available nodes in the network, as is shown in the below figure.
 The
facilitators of the network will be governed by the following rules that will be
stored in an acquaintance list:
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Each facilitator evaluates the items that arrives in its input queue on a FIFO
principle
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Only four requests can be processed by a
measurement period (epoch)
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The more time a facilitator spends
processing a request, the busier it will appear to be. This busyness is
calculated by calculating the previous and after busyness for the current epoch
in a 0.8 to 0.6 ratio.
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If a facilitator’s busyness is higher than
50% then the job is forwarded to the next available facilitator whose busyness
is less or equal to 50%
Optimization of the rules for a particular
application scenario is the subject of ongoing work.
In-Motes middleware has to overcome specific
limitations that are produced by the nature of WSNs. The MICA2 motes that we are
using have only a 128KB memory available for instructions and 4KB of data memory
while the microprocessor is an 8MHz Atmel 128. Another limitation derives from
the fact that TinyOS does not provide any dynamic memory management and as a
result all the data memory must be allocated statically. Also, the small size
batteries result in a low bandwidth wireless link of 38.4Kbaud which can be
considered quite unreliable. To address these challenges, in-Motes adapts
Agilla’s memory management for its agent instructions and tuplespaces. Also,
each agent is divided into tiny packets that are migrated and can be
retransmitted, minimizing the impact of message loss which is quite common in
mobile agents.
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