  Today, the advancements in urban technology have transformed into the concept
of smart cities. These smart cities are envisioned to be heavily dependent on
wireless sensor networks and internet of things. In this context, a number of
routing protocols have been proposed in literature for use in sensor networks.
We articulate on why these routing protocols need to be segregated on the basis
of their operational mechanism and utility, so that selection of these
protocols results in network longevity and improved performance. We classify
these protocols in four categories in terms of topology incognizant, data
centric, location assisted and mobility based protocols. We identify the
prevailing open issues to make space for more productive research and propose
how these categories may be useful in terms of their operational utility.
