Antonio Cianfrani

An OSPF-Integrated Routing Strategy for QoS-Aware Energy Saving in IP Backbone Networks

This paper deals with an energy saving routing solution, called Energy Saving IP Routing (ESIR), to be applied in an IP network. ESIR operation is integrated with Open Shorthest Path First (OSPF) protocol and allows the selection of the links to be switched off so that the negative effects of the IP topology reconfiguration procedures are avoided. The basic mechanisms which ESIR is based on are the concepts of SPT exportation and move. These mechanisms allow to share a Shortest Path Tree (SPT) between neighbor routers, so that the overall set of active network links can be reduced. Properties of moves are defined and the energy saving problem in an IP network is formulated as the problem of finding the Maximum Set of Compatible Moves (MSCM). The MSCM problem is investigated in two steps: firstly, a relaxed version of the problem, named basic MSCM problem, is considered in which QoS requirements are neglected; in the second step, the solution of the full problem, named QoS-aware MSCM problem, is faced. We prove that the basic MSCM problem can be formulated as the well-known Maximum Clique Problem in a graph; instead the QoS-aware MSCM introduces a condition equivalent to the Knapsack problem. ILP formulations to solve both the problems are given and heuristics to solve them in practical cases are proposed. The performance evaluation shows that in a real ISP network scenario ESIR is able to switch off up to 30% of network links by exploiting over-provisioning adopted by operators in the network resource planning phase and typical daily traffic trend.

Enabling backbone networks to sleep

Today, backbone networks of telecom operators deploy a large number of devices and links. This is mainly due to both redundancy purposes for network service reliability and resource overdimensioning for maintaining quality of service during rush hours. Unfortunately, current network devices do not have power management primitives, and have constant energy consumption independent of their actual workloads. Starting from these considerations, we propose a viable approach to introduce and support standby modes in backbone network devices. This approach can be effectively used to almost halve the energy requirements of the whole telecom core network. Our main idea consists of periodically reconfiguring nodes and links to meet incoming traffic volumes and operational constraints of real-world networks, such as reliability, stability, quality of service, and reconvergence times. To this purpose, the approach we propose directly exploits the main features of both backbone device architectures and the network protocol stack.

An OSPF enhancement for energy saving in IP networks

This paper deals with a strategy to save energy in an IP network during low traffic hours allowing a subset of IP router interfaces to be put in sleep mode by means of an Energy Aware Routing (EAR) strategy. The EAR is fully compatible with OSPF and is based on the “Shortest Path Tree (SPT) exportation” mechanism, consisting in sharing the SPTs among couple of routers. The EAR strategy is able to control the set of links to be put in sleep mode through the concept of “move”. This approach gives the network operator the possibility to control the network performance and allows a smoothed QoS degradation strategy to be implemented. A formulation of the EAR problem is presented and will be demonstrated that this problem can be traced back to the well-known problem of the maximum clique search in an undirected weighted graph. A heuristics, called Max Compatibility, is presented and, as shown in the performance evaluation study, it allows to save about 30% of network links with a negligible increase of network path lengths and link loads.

Network pruning for energy saving in the Internet

Many scientific works propose methods of reducing the amount of energy consumed by the Internet. Although the structure of the Internet was not developed with specific attention to energy consumption, there are various components on which it is possible to act. In our work, we analyze the possibility of affecting the topology of the network. We propose a heuristic called Energy Saving based on TOPology control (ESTOP), which identifies poorly used router line cards by leveraging certain topological properties of the graph modeling an Internet Service Provider (ISP). By acting on these line cards - for example, by putting them into sleep mode - we prune the Internet topology and achieve significant energy savings while preserving the primary topological characteristics of the pruned network. Although ESTOP is traffic-unaware, we assess its behavior under real traffic loads, demonstrating that its performance is comparable to the more complex traffic-aware solutions proposed in the literature.

Keeping the connectivity and saving the energy in the internet

Nowadays a big effort is spent to reduce the Internet energy consumption. Actual Internet topologies have space to power off some links and devices to reduce the energy consumed in off-peak periods still guaranteeing connectivity among terminals. In this work we leverage the algebraic connectivity of the graph modeling an ISP network in order to define the ESACON (Energy Saving based on Algebraic CONnectivity) algorithm. We then consider the network connectivity as a first target performance to be assured. To this aim we identify a metric based on the algebraic connectivity that, on one side, allows to switch off several links with the consequent significant energy saving and, on the other side, still preserves network connectivity and network performance for efficiently supporting the Internet traffic. We find that ESACON achieves better performance with respect to similar topology-aware approaches; moreover ESACON performance are comparable with ones of a complex traffic-aware solution.

Thermal-Aware Scheduling of Batch Jobs in Geographically Distributed Data Centers

Decreasing the soaring energy cost is imperative in large data centers. Meanwhile, limited computational resources need to be fairly allocated among different organizations. Latency is another major concern for resource management. Nevertheless, energy cost, resource allocation fairness, and latency are important but often contradicting metrics on scheduling data center workloads. Moreover, with the ever-increasing power density, data center operation must be judiciously optimized to prevent server overheating. In this paper, we explore the benefit of electricity price variations across time and locations. We study the problem of scheduling batch jobs to multiple geographically-distributed data centers. We propose a provably-efficient online scheduling algorithm - GreFar - which optimizes the energy cost and fairness among different organizations subject to queueing delay constraints, while satisfying the maximum server inlet temperature constraints. GreFar does not require any statistical information of workload arrivals or electricity prices. We prove that it can minimize the cost arbitrarily close to that of the optimal offline algorithm with future information. Moreover, we compare the performance of GreFar with ones of a similar algorithm, referred to as T-unaware, that is not able to consider the server inlet temperature in the scheduling process. We prove that GreFar is able to save up to 16 percent of energy-fairness cost with respect to T-unaware.

A Survey on Energy-Aware Design and Operation of Core Networks

A detailed survey of approaches reducing energy consumption of core networks is presented in this paper. We consider a multilayer architecture, in which the optical layer can be realized either with a Wavelength Division Multiplexing (WDM) network or an Elastic Optical Network (EON). We focus on the design and operation stages, i.e., deciding which devices to install in the network during the former step, and choosing which devices to put into sleep mode during the latter one. A taxonomy for classifying the surveyed approaches is provided in order to compare the works covering energy efficiency in core networks (in terms of both optimal formulations and heuristic solutions). Moreover, our work provides a global view of the traffic assumptions, the topologies, and the power consumption models in the literature. The need of further investigations in this field clearly emerges. We envision future works targeting: (1) more effective standardization efforts to practically realize sleep modes; (2) the evaluation of the impact of sleep mode on the device lifetime; (3) the extensive adoption of new paradigms like Software Defined Networking (SDN) and EON; and (4) a radical improvement in the testbed implementations.

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.

Achieving Sub-Second Downtimes in Large-Scale Virtual Machine Migrations with LISP

Nowadays, the rapid growth of Cloud computing services is stressing the network communication infrastructure in terms of resiliency and programmability. This evolution reveals missing blocks of the current Internet Protocol architecture, in particular in terms of virtual machine mobility management for addressing and locator-identifier mapping. In this paper, we propose some changes to the Locator/Identifier Separation Protocol (LISP) to cope with this gap. We define novel control-plane functions and evaluate them exhaustively in the worldwide public LISP testbed, involving five LISP sites distant from a few hundred kilometers to many thousands kilometers. Our results show that we can guarantee service downtime upon live virtual machine migration lower than a second across American, Asian and European LISP sites, and down to 300 ms within Europe, outperforming standard LISP and legacy triangular routing approaches in terms of service downtime, as a function of datacenter-datacenter and client-datacenter distances.

Sleep modes effectiveness in backbone networks with limited configurations

In this work we propose a strategy to minimize the impact of energy saving techniques on the performance of an Internet Service Provider network. We study the problem of putting in sleep mode links of a backbone network, while limiting the number of times each device changes its power state (full power mode or sleep mode). Our aim is to limit the number of network configurations, i.e., the change of the current set of network links at full power. We tackle the problem both analytically and by simulations. We first present a model, based on random graph theory, to compute the links energy saving given a traffic variation, QoS requirements, and the number of allowed network configurations. The same analysis is then repeated over two realistic case studies, and with realistic algorithms to choose the set of links in sleep mode. Results show (both analytically and by simulation) that the energy savings with few configurations (two or three per day) are close to the maximum one, in which a new configuration is applied for each traffic matrix. Moreover, we show that few configurations per day limit the number of overhead messages required for exchanging information about the device state. Thus, we can conclude that a practical implementation of sleep mode strategies for network operators is to define, on the basis of typical traffic trend, few configurations to be activated in specific time instants.