Despite the growing concern for the energy consumption of the Internet, green strategies for network and traffic management cannot undermine the quality and the functional level normally expected from carrier networks. In particular, two very important issues that may be affected by green networking techniques are resilience to node and link failures, and robustness to traffic variations.

In this paper, we study how strategies aiming at achieving different levels of resiliency and robustness impact the efficiency of energy-aware network management approaches in saving energy. We propose novel optimization models to minimize the energy consumption of IP networks that explicitly guarantee network survivability to failures and robustness to traffic variations. Network consumption is reduced by putting in sleep mode idle line cards and nodes according to daily traffic variations that are modeled by dividing a single day into multiple time intervals. To guarantee network survivability we consider two different schemes, dedicated and shared protection, which assign a backup path to each traffic demand and some spare capacity on the links along the path. Robustness to traffic variations is provided through an approach that allows to tune the capacity margin on active links in order to accommodate load variations of different magnitude. Furthermore, we impose some inter-period constraints necessary to guarantee network stability and preserve device lifetime. Both exact and heuristic methods are proposed.

Experimentations carried out on realistic networks operated with flow-based routing protocols (like MPLS) allow us to quantitatively analyze the trade-off between energy cost and level of protection and robustness. Results show that with optimal strategies significant savings, up to 30%, can be achieved even when both survivability and robustness are fully guaranteed.