Alessandro Valenti

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.

QoE and QoS comparison in an anycast digital television platform operating on passive optical network

We report an experimental investigation on QoE, compared with the QoS, for a complete digital television platform able to deliver broadcast, multicast and unicast services in wide geographical area network, with broadband access based on passive optical network (PON). In particular, we show the service degradation due both to network impairments and to the TCP limits on operating systems. Multicast forwarding was tested in PBB-TE environment to exploit a Carrier Ethernet behavior. Concerning broadcasting, such a network allows the user to see the DVB-T by using the same optical infrastructure by means of the specific wavelength foreseen by the GPON standard.

Network Performance Investigation in a Wide Area Gigabit Ethernet Test Bed Adopting All-Optical Wavelength Conversion

We experimentally investigate the network performance of a wide area gigabit Ethernet test bed in which we introduced the all-optical wavelength conversion (WC) process. Such a test bed is configured to implement a quality of service (QoS) control based on the virtual private local area network service (VPLS), a technique that, according to the reported results, is well suitable to implement forwarding process based on dedicated wavelengths. We show that the all-optical WC does not degrade the QoS properties of the VPLS and it can be used with very fast switching time.

On the Impact of Operative Systems Choice in End-User Bandwidth Evaluation: Testing and Analysis in a Metro-Access Network

In this work, we apply an accredited standard technique for end-user bandwidth evaluation in an ADSL access scenario and show that the choice of operating system has a critical impact on performances. In particular, our end-to-end File Transfer Protocol (FTP)-based bandwidth measurements point out the strong impact of TCP (Transmission Control Protocol) implementation. As a consequence, a testing scenario needs to be described not only according to the physical parameters, but also paying attention to software implementation factors that could affect the testing results.

Experimental Investigation of Quality of Service in an IP All-Optical Network Adopting Wavelength Conversion

We experimentally show how the virtual private large-area network service (VPLS) technique, a layer 2 service, can improve optical network performance in terms of quality of service (QoS), and how a VPLS network behaves when it adopts all-optical wavelength conversion (AOWC), a new optical process that will be introduced in future optical networks. The advantages of VPLS are based on the capability to generate logical reliable paths in each wavelength channel, permitting suitable partitioning of the bandwidth according to the user requirements. In particular, we show the advantages of VPLS in access networks based on passive optical networks, and we test QoS properties of VPLS paths when an AOWC process occurs both in the core and in the access networks. The experimental investigation is carried out in a wide-area, all-optical gigabit Ethernet testbed with an access section based on an Ethernet passive optical network. As far as the core segment is concerned, we chose a high-efficiency AOWC process based on four-wave mixing in dispersion-shifted fiber; conversely in the access segment we chose a cheaper AOWC process based on cross gain modulation in a semiconductor optical amplifier. The reported results show that gigabit Ethernet transmission, with the relative layer 2 techniques, is also well suitable for wide-area WDM architectures, and in particular it is able to guarantee end-to-end QoS for huge bandwidth services such as high-definition TV and also in the case of congestion, restoration, and wavelength conversion processes.

Wavelength path optimization in optical transport networks for energy saving

Today Energy Consumption is one of the fundamental topics also for telecommunication networks. In this paper, we report a numerical investigation about energy saving in a transport network both exploiting the transmission properties that permit to reduce 3R equipments and reducing optical links during low traffic periods.

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.