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Resumo(s)
In beacon-enabled mode, IEEE 802.15.4 is ruled by the slotted
CSMA/CA Medium Access Control (MAC) protocol. The standard
slotted CSMA/CA mechanism does not provide any means of
differentiated services to improve the quality of service for timecritical
events (such as alarms, time slot reservation, PAN
management messages etc.). In this paper, we present and discuss
practical service differentiation mechanisms to improve the
performance of slotted CSMA/CA for time-critical events, with only
minor add-ons to the protocol. The contribution of our proposal is
more practical than theoretical since our initial requirement is to
leave the original algorithm of the slotted CSMA/CA unchanged, but
rather tuning its parameters adequately according to the criticality of
the messages. We present a simulation study based on an accurate
model of the IEEE 802.15.4 MAC protocol, to evaluate the
differentiated service strategies. Four scenarios with different settings
of the slotted CSMA/CA parameters are defined. Each scenario is
evaluated for FIFO and Priority Queuing. The impact of the hiddennode
problem is also analyzed, and a solution to mitigate it is
proposed.