Abstract-DemandResponse is a mechanism used in power grids to manage customers' power consumption during critical situations (e.g. power shortage). Data centres are good candidates to participate in Demand Response programs due to their high energy use. In this paper, we present a generic architecture to enable Demand Response between Energy Provider and Data Centres realised in All4Green. To this end, we show our three-level concept and then illustrate the building blocks of All4Green's architectural design. Furthermore, we introduce the novel aspects of GreenSDA and GreenSLA for Energy Provider-Data centre sub-ecosystem as well as Data centre-IT Client sub-ecosystem respectively. In order to further reduce energy consumption and CO2 emission, the notion of data centre federation is introduced: savings can be expected if data centres start to collaborate by exchanging workload. Also, we specify the technological solutions necessary to implement our proposed architectural approach. Finally, we present preliminary proof-of-concept experiments, conducted both on traditional and cloud computing data centres, which show relatively encouraging results. I. OVERVIEWWith the energy consumption of ICT mushrooming for some decades, and data centres at the heart of this development, a lot of research has been dedicated to this huge problem for environmental health and resource depletion. However, it turns out that data centres are not only part of the problem but also one key to its solution because the energy challenge is both, a problem of energy consumption and a problem of power consumption: In times of low supply and high demand, extra power needs to be provided at high environmental cost, in times of high supply (e.g. through wind and sun) and low demand, superfluous energy suppliers are cut off the electricity net. The project All4Green1 shows that data centres with their huge power hunger can play a role in solving this challenge. To this end, the data centre is viewed as part of an ecosystem consisting of ICT users deploying services in the data centre, electrical power providers, and data centres cooperating in a federated way. By establishing a collaborative scheme within this eco-system through green contracts supported by an underlying signalling technology, All4Green tackles both goals: It aims at saving CO 2 emissions by enabling a cleaner energy mix for the energy consumption of a data centre. And additionally it will reduce this energy consumption by 10%.All4Green relevant actors in the system, as illustrated in Fig. 1 The All4Green approach is based on a three-levels-concept

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