Angelo Coiro

Reducing Power Consumption in Wavelength Routed Networks by Selective Switch Off of Optical Links

In this paper, the power consumption of a transparent circuit-switched wavelength-division multiplexing (WDM) optical network is evaluated, considering client flow protection requirements and the daily traffic variability. Moreover, a simple heuristic algorithm is applied to the considered network scenario to reduce the power consumption of optical links. When traffic load decreases, the algorithm tries to switch off optical links according to several heuristic criteria that take into account the power consumption parameter of links, some topological consideration and the congestion of each fiber. By performing such an optimization, applying the best link-ordering criterion, it is possible to save an amount of power from 28% up to 86% of the power consumed by optical links on the basis of the traffic load. This leads to an average energy saving of 35% with respect to the energy consumed by the whole optical network. Moreover, we evaluate the impact of network design parameters on the proposed algorithm and the network power consumption. Results show that, for a 18-node network supporting an average traffic of 75 Gbits/s between each node pair, a number of wavelengths equal to 80 can drastically reduce the power consumption of optical links.

Power-Aware Routing and Wavelength Assignment in Multi-Fiber Optical Networks

This paper focuses on the energy consumption minimization problem of an optical transport network extending over a very wide area. In particular, the specific problem of power-aware routing and wavelength assignment (PA-RWA) is addressed considering a transparent multi-fiber optical network. An integer linear programming formulation is provided for the static lightpath establishment problem and a few heuristics are proposed to solve the problem in the case of dynamic lightpath establishment. To solve the routing problem we propose a novel algorithm named load based cost; it is based on a cost function that considers the load of each optical fiber to compute link weights. We also propose two new wavelength assignment algorithms: the first one is derived from the first fit heuristic whilst the second one is based on an innovative approach. It works like a least cost routing algorithm assigning a cost to each wavelength for each link in the path and then minimizes the total cost. Our proposal is compared with a number of already known RWA algorithms showing that it is able to reduce the power consumption of the network by about 20-30%, depending on the amount of traffic treated, with respect to state of the art algorithms with a difference of about 10% with respect to the lower bound. In order to provide a complete analysis of the feasibility of the proposed heuristics, the blocking probability is evaluated: the results show that, unlike the other power-aware algorithms here considered, our proposal shows a low impairment with respect to the least congested path-first fit alternative. Another important result regards the better performance of the proposed wavelength assignment algorithm with respect to first fit.

Dynamic Power-Aware Routing and Wavelength Assignment for Green WDM Optical Networks

This paper proposes a novel power-aware routing and wavelength assignment (PA-RWA) algorithm to be applied to a transparent wavelength division multiplexing (WDM) optical network. The proposed algorithm aims at improving the energy efficiency of the optical network by leaving unused optical fibres as much as possible in order to minimize the number of optical amplifiers kept active in the network. A dynamic lightpath establishment scenario is considered and results are compared with other routing algorithms showing that the proposed algorithm can drastically reduce the power consumption for any value of traffic load.

Energy-aware traffic engineering: A routing-based distributed solution for connection-oriented IP networks

The present paper deals with energy saving in IP networks and proposes a distributed energy-aware traffic engineering solution, named DAISIES, for switching off network links according to traffic variations. DAISIES works in a connection-oriented network, e.g. an IP/MPLS network, and follows a routing-based approach, i.e. it acts on the routing algorithm whilst link switch-off/on are consequence of routing decisions. The basic idea is to re-compute the path of each traffic demand when its requested capacity changes. A specific cost function is used to compute link weights into the shortest path routing algorithm with the goal of keeping unused as many links as possible. The main advantages of DAISIES can be summarized as follows: (i) no changes are required to current routing and signaling protocols, (ii) packet loss is completely avoided, (iii) both traffic decreasing and increasing and changing network conditions are automatically managed, and (iv) link switch-off/on take place transparently to the routing protocol and to other nodes. The performance of the proposed solution is evaluated in terms of energy saving relative to a static network optimized to support the peak traffic. Results show that DAISIES is able to save about 30% of energy in several traffic conditions. Moreover, it is shown that it is possible keeping the additional complexity low and still reaching high energy efficiency.

TREND in energy-aware adaptive routing solutions

Energy saving in telecommunications networks has become a well established topic in the research community. We look at the electrical and optical layers of IP-over-WDM networks, and present a list of evaluation criteria for energy- aware adaptive routing solutions (EA-ARSs) from the perspective of a network operator. Furthermore, we briefly explain the adaptive routing solutions originating from the European Unions TREND and the FP7 Network of Excellence, show saving of energy consumed by line cards in a reference scenario, and use the evaluation criteria to identify the next steps toward introduction of the EA-ARSs into real operation.

Distributed and Adaptive Interface Switch Off for Internet Energy Saving

This work proposes a distributed and adaptive mechanism for saving energy in IP/MPLS over WDM networks by switching off router line cards according to the traffic variability in the network. The proposed mechanism optimizes the traffic routing and adapts the IP topology to the traffic that is actually carried in the network. This is done by re- computing the path of each traffic flow several times during a day when their requested capacity changes. The routing is performed by using a specific cost function, named V-Like, to compute link weights into the shortest path routing algorithm. The proposed solution is compared with a static energy-aware heuristic algorithm proposed in the literature; results show that it is possible to save from 35% up to 50% of energy with respect to the static case, depending on the traffic load.

Facing the Reality: Validation of Energy Saving Mechanisms on a Testbed

Two energy saving approaches, called Fixed Upper Fixed Lower (FUFL) and Dynamic Upper Fixed Lower (DUFL), switching off idle optical Gigabit Ethernet (GbE) interfaces during low traffic periods, have been implemented on a testbed. We show on a simple network scenario that energy can be saved using off-the-shelf equipment not explicitly designed for dynamic on/off operation. No packet loss is experienced in our experiments. We indicate the need for faster access to routers in order to perform the reconfiguration. This is particularly important for the more sophisticated energy saving approaches such as DUFL, since FUFL can be implemented locally.

Increasing device lifetime in backbone networks with sleep modes

We study the impact of sleep modes capabilities on the lifetime of backbone devices. We first define a model that integrates sleep modes in the device lifetime. We then derive a model for the network topology to compute the average network lifetime. Finally, we consider a realistic case study driven by operator feedback. Results indicate that the application of sleep modes can increase the average network lifetime. However, frequent power state transitions of network devices can deteriorate the network lifetime. Thus, we argue that the design and the management of energy-aware networks need to take into account the device lifetime.

Reducing power consumption in backbone IP networks through table lookup bypass

We study the possibility of bypassing the table lookup capability of router linecards to save energy in IP networks. Differently from previous works, the table lookup operation is bypassed independently for each linecard. We first present a model for our scenario. Then, the problem is formally stated as an optimization problem. Moreover, we provide a genetic algorithm to solve the problem up to medium sized network. We evaluate the performance of the optimal solution and the genetic algorithm on synthetically generated topologies. We then consider large topologies available in the literature to evaluate the performance of our algorithm. We compare the table lookup operation with the traditional operation of switching off the linecards. Results show that in general the table lookup operation achieve higher energy savings than the simple switch off. Then, we consider the impact of jointly applying the two techniques to further increase the energy savings. In this case, we show that the saving can be further increased by application of the two techniques.

Impact of energy-aware topology design and adaptive routing at different layers in IP over WDM networks

As the Internet expands in terms of users and exchanged traffic, its energy consumption is becoming a very important issue; in particular, the energy consumption of core networks is expected to be the most critical aspect in coming years. Different strategies and many solutions have been proposed in the last years to improve the energy efficiency of core networks. Specifically, three different strategies can be mainly distinguished: i) the Energy Minimized Virtual Topology Design (EM-VTD), which aims at designing the IP layer topology minimizing the peak power consumption of the network; ii) the Energy Aware Traffic Engineering (EA-TE), which acts on the traffic routing at the IP layer and aims at bringing the power consumption of the network nearly proportional to the actual offered load; iii) the Power Aware Routing and Wavelength Assignment (PA-RWA), which instead acts on the traffic routing at the optical layer. The present study considers these three energy saving strategies, adopting a specific solution for each of them, and evaluates the impact that each of them has on the power consumption of the whole network, considering both the IP and the WDM layers. Results show that a good design of the IP topology is a key aspect to improve the energy efficiency of the network with respect to other simpler strategies (e.g. the end-to-end or the link-by-link grooming strategy). Moreover, the combined use of adaptive routing solutions at both the IP and the WDM layers allows to achieve a better comprehensive power saving in any traffic load conditions, with IP-specific solutions being more important when the total traffic offered to the network grows.