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Mixed deployment of sleep-enabled and non-sleep-enabled router cards is suggested at each node of an IP over WDM network along with survivability and security constraints. This is used to design a green network which is observed to reduce energy consumption (by up to 28% for an example network) compared to a network where the router cards are not sleep-enabled.OCIS codes: (060.4250) Networks; (060.4256) Networks, network optimization IntroductionThe ever-increasing volume of Internet traffic requires more and more network equipments resulting in high energy consumption in the network. As stated in [1], reducing the energy consumption in communication networks is driven both by ecological motivations towards reduction of CO 2 emissions as well as economic ones, in order to keep operational costs (OPEX) down by reducing electricity consumption in the network. This has motivated several research efforts towards the design and implementation of energy-efficient networks. A common approach for achieving higher energy efficiency is to turn off network devices selectively when they are not needed or put some of them into a sleep mode (low power state) when the traffic falls below a certain predetermined threshold [2,3]. However, this strategy can create problems when network survivability and security are important. Turning off network devices can impact the network's overall connectivity and this in turn would have a negative impact on network survivability [2]. Moreover, enabling software control to turn off network devices or put them into a sleep mode may also lay the network open to hostile attacks, i.e., a hostile attacker can turn off or put to sleep a large part or even all of the network devices in order to paralyze the entire core IP over WDM network. It should also be noted that network devices which can be put into a sleep mode are generally more expensive than devices which do not have this feature and using the former will increase the overall network cost. Therefore, designing an energyefficient IP over WDM network will imply tradeoffs between the network's energy consumption, cost, and its survivability and security.IP routers in an IP over WDM network are generally considered to be both the most energy-hungry [4] and the most expensive. Therefore, the network device that we focus on in this paper is the IP router. We also assume that the power consumption of a router's line cards constitute the total power consumption of the IP router [5 6]. Viewing the traffic day-night pattern and considering the additional requirements of network survivability and security, we configure a mix of sleep-enabled router cards and non-sleep-enabled router cards at each network node, where some or all the sleep-enabled router cards may be put to sleep to save energy when the network traffic is low.

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