  In this paper, network function virtualization (NFV) is identified as a
promising key technology that can contribute to energy-efficiency improvement
in 5G networks. an optical network supported architecture is proposed and
investigated in this work to provide the wired infrastructure needed in 5G
networks and to support NFV towards an energy efficient 5G networks. In this
architecture the mobile core network functions as well as baseband function are
virtualized and provided as VMs. the impact of the total number of active users
in the network, backhaul/fronthaul configurations and VM inter-traffic are
investigated. A mixed integer linear programming (MILP) optimising model is
developed with the objective of minimising the total power consumption by
optimizing the VMs location and VMs servers' utilisation. The MILP model
results show that virtualization can result in up to 38% (average 34) energy
saving. The results also reveal how the total number of active users affects
the baseband VMs optimal distribution whilst the core network VMs distribution
is affected mainly by the inter-traffic between the VMs. For real-time
implementation, two heuristics are developed an Energy Efficient NFV without
CNVMs inter-traffic (EENFVnoITr) heuristic and an Energy Efficient NFV with
CNVMs inter-traffic (EENFVwithITr) heuristic, both produce comparable results
to the optimal MILP results
