  Access networks, in particular, Digital Subscriber Line (DSL) equipment, are
a significant source of energy consumption for wireline operators. Replacing
large monolithic DSLAMs with smaller remote DSLAM units closer to customers can
reduce the energy consumption as well as increase the reach of the access
network. This paper attempts to formalize the design and optimization of the
"last mile" wireline access network with energy as one of the costs to be
minimized. In particular, the placement of remote DSLAM units needs to be
optimized. We propose solutions for two scenarios. For the scenario where an
existing all-copper network from the central office to the customers is to be
transformed into a fiber-copper network with remote DSLAM units, we present
optimal polynomial-time solutions. In the green-field scenario, both the access
network layout and the placement of remote DSLAM units must be determined. We
show that this problem is NP-complete. We present an optimal ILP formulation
and also design an efficient heuristic-based approach to build a
power-and-cost-optimized access network. Our heuristic-based approach yields
results that are very close to optimal. We show how the power consumption of
the access network can be reduced by carefully laying the access network and
introducing remote DSLAM units.
