The precision
of the synchronized clocks depends on the needs of the applications. For example,
a sensor network requiring TDMA service may require microseconds
di?®erence among the neighbor nodes while a data gathering application for
sensor networks requires only milliseconds of precision.
As sensor networks are application driven, the design challenges of a time
synchronization protocol are also dictated by the application. These challenges
are to provide an overall guideline and requirement when considering the features
of a time synchronization protocol for sensor networks; they are robust,
energy aware, server-less, light-weight, and tunable service.
??? Robust: Sensor nodes may fail, and the failures should not have signifi-
cant e?®ect on the time synchronization error. If sensor nodes depend on
a specific master to synchronize their clocks, a failure or anomaly of the
master??™s clock may create a cascade e?®ect that nodes in the network may
become unsynchronized. So, a time synchronization protocol has to handle
the unexpected or periodic failures of the sensor nodes. If failures do occur,
the errors caused by these failures should not be propagated throughout
the network.
??? Energy aware: Since each node is power/energy limited, the use of resources
should be evenly spread and controlled. A time synchronization
protocol should use the minimum number of messages to synchronize the
nodes in the earliest time.
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