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\chapter{Historical Developments in WSNs Routing}
\label{Chapter:2}
%\lhead{CHAPTER 2. \emph{}}

\section{Introduction}
Network layer is one of the most explored research domain in WSNs, as number of network layer routing algorithms and protocols have been proposed for past couple of years. The major role of the network layer is to find routes from SNs  to BS for delivery of data events. In particular, there are two primary models followed  for data routing in WSNs namely \emph{single-hop} and \emph{multi-hop}.
