  Balanced energy consumption is a major research concern in sensor networks.
If some sensor nodes spent energy rapidly compared to other sensor groups, then
the energy consumption is not evenly distributed and the lifetime of the
network is adversely affected. In cluster-based communication protocol,
cluster-head nodes rapidly dissipate their energy compared to respective
cluster members as it has additional duties of receiving data from cluster
members and aggregation of received data. Clustering protocols periodically
rotate the energy-intensive job of cluster-head among other sensors in order to
evenly distribute the CH's energy load. In this paper, we review various
cluster-head rotation approaches and classify them into different categories
based on the number of participating nodes, rotation mechanism, and decision
parameter(s). Finally, we discuss open research issues in developing an
efficient cluster-head rotation approach, which reduces the premature death of
cluster-head nodes and maximizes the network lifetime.
