Energy saving in access networks: Gain or loss from the cost perspective?

Energy consumption in telecommunication networks has become a significant problem during the last few years. Many energy efficient mechanisms have been proposed and evaluated with respect to their impact on the overall network performance (e.g., delay, blocking probability, quality of transmission). Most of these mechanisms are based on the sleep mode functionality, i.e., a “low power” state of network devices that can be utilized in low traffic conditions. On the other hand, a frequent switching between a working and a sleeping state may increase the probability of failures in a device, which in turn makes the operational cost related to fault reparation higher. This paper discusses how sleep mode-based energy saving mechanisms can impact the reliability performance of network equipment by pointing out several physical phenomena that may lead to an increase of the failure rate. In order to quantify such effects we propose a methodology that estimates to what extent energy savings can be maximized without exceeding the extra reparation cost caused by the degradation of the reliability performance of network equipment due to frequent switching on and off. We perform a number of simulative studies focused on an optical access segment and show that the cost saved by reducing the energy consumption (i.e., as the result of a power efficient mechanism) may be easily overcome by the extra expenses related to reparation of network equipment and service interruption for business users.