Dynamic spectrum management (DSM) is recognized as a promising technology to reduce power consumption in DSL access networks. However, the correct formulation of power-aware DSM problem statements requires a proper understanding of greening, i.e., reducing power consumption. In this paper, we, therefore, investigate greening and show that it can be decomposed into two dimensions: the price of greening and the fairness of greening. We first analyze the price of greening, providing theoretical bounds on the power-rate trade-off and identifying the typical trends that can be expected in practice, with some particularly promising results. Then, we introduce the fairness dimension, where we show that fairness becomes crucial when reducing power consumption. We propose four different fair greening policies that can be used to obtain a favorable trade-off between fast, fair and green DSL operation. Finally, we evaluate and quantify the corresponding trade-offs for realistic DSL access networks.
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