"The present document specifies the method and metrics to determine the energy efficiency of operational Network Function Virtualisation (NFV) applications and their associated infrastructure when that infrastructure is implemented outside the boundaries of the access fixed@ cable and mobile networks which they serve. The present document: ? Extends the Objective KPIs of ETSI EN 305 200-2-2 [i.2] (fixed access networks) and ETSI EN 305 200-2-3 [i.3] (mobile access networks) to assess the impact of NFV when applied to those networks as described in ETSI GR NFV 001 [i.4]. ? Does not consider any assessment of energy saved by the implementation of NFV as there can be no timestamped comparison of an operational infrastructure from which functions have been removed to a virtualized environment. NOTE: In an ICT network (e.g. a fixed access network) comprising many Network Distribution Nodes (NDNs) with different loading levels it is not clear that there will always be an energy consumption benefit - the more relevant benefit being network and operational flexibility (such as reduced maintenance or increased reliability). The present document: ? Does not address the operational energy efficiency of specific Information Technology Equipment (ITE) such as servers which may provide NFV facilities. Other ETSI EN documents (e.g. ETSI EN 303 470 [i.1]) have been prepared to address such factors. ? Does not specify any assessment of the overall effectiveness of an NFV implementation although it contains information in an informative annex regarding the technical milestones that would be required for this to be addressed in a future revision of the present document. The KPIs specified are primarily intended for trend analysis - not to enable comparison between individual implementations of NFV unless the conditions of operation are ""similar""."