  Reducing CO2 emissions is an important global environmental issue. Over the
recent years, wireless and mobile communications have increasingly become
popular with consumers. An increasingly popular type of wireless access is the
so-called Wireless Mesh Networks (WMNs) that provide wireless connectivity
through much cheaper and more flexible backhaul infrastructure compared with
wired solutions. Wireless Mesh Network (WMN) is an emerging new technology
which is being adopted as the wireless internetworking solution for the near
future. Due to increased energy consumption in the information and
communication technology (ICT) industries, and its consequent environmental
effects, energy efficiency has become a key factor to evaluate the performance
of a communication network. This paper mainly focuses on classification layer
of the largest existing approaches dedicated to energy conservation. It is also
discussing the most interesting works on energy saving in WMNs networks.
