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 efficient polynomial-time solutions. For the green-field scenario, where 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 planning the access network and introducing remote DSLAM units.

IEEE 802.16 standard was designed to support the bandwidth demanding applications with quality of service (QoS). Bandwidth is reserved for each application to ensure the QoS. For variable bit rate (VBR) applications, however, it is difficult for the subscriber stations (SSs) to predict the amount of incoming data. To ensure the QoS guaranteed services, the SS may reserve bandwidth more than the amount of its transmitting data. As a result, the reserved bandwidth may not be fully utilized all the time. In this paper, we propose a scheme, named Bandwidth Recycling, to recycle the unused bandwidth without changing the existing bandwidth reservation. The idea of our scheme is to allow other SSs to utilize the unused bandwidth when it is available. Thus, not only the same QoS guaranteed services can be provided but also the system throughput can be improved. Mathematical analysis and simulation are used to evaluate the proposed scheme. Simulation and analysis results confirm that our proposed scheme can recycle 35 percent of unused bandwidth on average. By analyzing factors affecting the recycling performance, three scheduling algorithms are proposed to improve the overall throughput. The simulation results show that our proposed algorithm can further improve the overall throughput by 40 percent when the network is in the steady state.