Survivable virtual network mapping to provide content connectivity against double-link failures

In recent years, large scale natural disasters (such as earthquakes, or tsunami) have caused multiple Internet outages in different parts of the world, resulting in high infrastructures damages and capacity losses. Content providers are currently investigating novel disaster-resiliency mechanisms to maintain the service continuity in their Content Delivery Networks (CDNs). In case of such widespread failures, the content providers might not be able to guarantee Network Connectivity (i.e., the reachability of all nodes from any node in the network) and researchers have started investigating the concept of Content Connectivity (i.e., the reachability of the content from any point of the network), that can be achieved even when the network is disconnected, as long as a replica of the content can be retrieved in all the disconnected components of the network. In this paper we focus on double-link failures and consider different combinations of content connectivity and network connectivity. As guaranteeing network connectivity against double-link failures may result in very high network-resource consumption, in this work we present an Integer Linear Programming (ILP) formulation for survivable virtual network mapping to guarantee the network connectivity after single-link failures and maintain the content connectivity after double-link failures. We show that maintaining content connectivity against double-link failures costs almost the same, in terms of network resources, as providing network connectivity against single-link failures. We also investigate the trade-off between datacenter placement and the amount of resources needed to provide content connectivity in case of double-link failures

Power reduction strategies with differentiated quality of protection in IP-over-WDM networks

This work considers two important aspects of modern communication networks, network survivability, and energy efficiency. Survivability is a design requirement to provide failure recovery against network outages such as fiber cuts. To ensure survivability, traditionally, spare network (i.e., backup) resources are reserved in case of failures of primary (i.e., working) network resources. On the other hand, energy efficiency is required to cope with the continuous growth of the Internet traffic. Backup resources increase the energy consumption, especially if constantly powered-on. Hence, a trade-off between energy efficiency and network resiliency arises. To increase transport capacity and reduce energy consumption, wavelength division multiplexed (WDM) networks are adopted as the most practical solution for data transport in core networks, which are the focus of our work. In WDM networks, different levels of protection (i.e., dedicated, shared) can be implemented for different traffic demands, and different protection levels are characterized by different power consumptions. We consider a differentiated quality of protection (Diff-QoP) scheme where different levels of protection are provided. In this context, we investigate on two different power-reduction strategies to be used in protected WDM networks: (i) setting backup devices into low-power modes (sleep mode) and (ii) adapting the devices (i.e., transmitting/receiving equipment) usage to hourly traffic variations. We present exact modeling through Integer Linear Program (ILP) of the three scenarios and a provisioning algorithm to solve the problem of power minimized design of resilient optical core networks, under static and dynamic traffic conditions. We evaluate the performance of the proposed algorithm under static traffic conditions by comparing the obtained results with the optimal solution, in absence of traffic grooming. We show that the proposed heuristic reduces the computational time by three orders of magnitude with an optimality gap ranging from 8.88 up to 23.88%. Furthermore, we include traffic grooming and solve the problem under dynamic traffic conditions. Our findings show that enabling sleep mode (SM) for backup devices can help reduce total power consumption up to 20 and up to 38% when considering with Diff-QoP. Finally, adapting the number of transmitting/receiving devices to actual traffic needs guarantees power savings up to 80%, especially during off-peak hours

Virtual Network Function placement for resilient Service Chain provisioning

Virtualization technologies are changing the way network operators deploy and manage Internet services. In particular in this study we focus on the new Network Function Virtualization (NFV) paradigm, which consists in instantiating Virtual Network Function (VNFs) in Commercial-Off-The-Shelf (COSTS) hardware. Adopting NFV network operators can dynamically instantiate Network Functions (NFs) based on current demands and network conditions, allowing to save capital and operational costs. Typically, VNFs are concatenated together in a sequential order to form Service Chains (SCs) that provide specific Internet Services to the users. In this paper we study different approaches to provide the resiliency of SCs against single-link and single-node failures. We propose three Integer Linear Programming (ILP) models to solve the VNF placement problem with the VNF service chaining while guaranteeing resiliency against single-node/link, single-link and single-node failures. Moreover we evaluate the impact of latency of SCs on the VNFs distribution. We show that providing resiliency against both single-link and single-node failures necessitates the activation of twice the amount of resources in terms of nodes, and that for latency critical services providing resiliency against single-node failures comes at the same cost with respect to resiliency against single-link and single-nodes failures

Latency-and capacity-aware placement of chained Virtual Network Functions in FMC metro networks

Most of today's cloud applications are delivered by Cloud Service Providers (CSPs) on top of a physical network managed by one or multiple Infrastructure Providers (InPs). This new way of delivering services is impacting InPs' revenues, as InPs are only responsible for transporting data to users. Network Function Virtualization (NFV) was proposed to help InPs gain more flexibility in provisioning new services over their networks, hence achieving lower capital and operational costs, keeping stable revenue margins, and resisting the competition of CSPs (e.g., the “Over-The-Top”players). NFV aims at moving from the traditional approach of network functions running over dedicated hardware (e.g., firewall, NAT, etc.) into virtualized software modules running on top of Commercial Off The Shelf (COTS) equipment. However, deploying NFV in an operational network requires addressing two fundamental problems. The first consists on determining the locations where Virtual Network Functions (VNFs) will be hosted (i.e., VNF placement) and the second on how to properly steer network traffic to traverse the required VNFs in the right order (i.e, routing), thus provisioning network services in the form of Service Function Chains (SFCs). In this work we try to solve both problems focusing our analysis on a metro-regional scenario, where link bandwidth and COTS node processing capacity is inherently limited and where the current trend consists on moving towards a Fixed and Mobile Convergence (FMC) network infrastructure. We propose and compare different heuristic strategies for SFC provisioning, characterized by latency and/or capacity awareness (i.e., able to best exploit latency of links and/or processing capacity of COTS nodes for an effective placement of VNFs) and by the adoption of a load balancing policy for traffic routing, with the aim of maximally consolidating VNFs. We assess the benefits of our strategies against a state-of-the-art algorithm, both in terms of number of required COTS nodes in the metro/access network and of SFC acceptance ratio. Our findings indicate that combining latency and capacity awareness in the VNF placement process with a load-balancing routing strategy brings high benefits in terms of VNF consolidation and SFC acceptance ratio

A Survey on Network Resiliency Methodologies against Weather-based Disruptions

Due to the increasing dependence on network ser- vices of our society, research has recently been concentrating on enhancing traditional protection strategies to withstand large- scale failures, as in case of disaster events. The recently-formed EU-funded RECODIS project aims at coordinating and fostering research collaboration in Europe on disaster resiliency in com- munication networks. In particular, the Working Group (WG) 2 of the RECODIS project focuses on developing new network- resiliency strategies to survive weather-based disruptions. As a first step, WG2 members have conducted a comprehensive literature survey on existing studies on this topic. This paper classifies and summarizes the most relevant studies collected by WG2 members in this first phase of the project. While the majority of studies regarding weather-based disruptions deals with wireless network (as wireless channel is directly affected by weather conditions), in this survey we cover also disaster- resiliency approaches designed for wired network if they leverage network reconfiguration based on disaster “alerts”, considering that many weather-based disruptions grant an “alert” thanks to weather forecast

A survey on network resiliency methodologies against weather-based disruptions

Due to the increasing dependence on network services of our society, research has recently been concentrating on enhancing traditional protection strategies to withstand large scale failures, as in case of disaster events. The recently-formed EU-funded RECODIS project aims at coordinating and fostering research collaboration in Europe on disaster resiliency in communication networks. In particular, the Working Group (WG) 2 of the RECODIS project focuses on developing new network resiliency strategies to survive weather-based disruptions. As a first step, WG2 members have conducted a comprehensive literature survey on existing studies on this topic. This paper classifies and summarizes the most relevant studies collected by WG2 members in this first phase of the project. While the majority of studies regarding weather-based disruptions deals with wireless network (as wireless channel is directly affected by weather conditions), in this survey we cover also disaster resiliency approaches designed for wired network if they leverage network reconfiguration based on disaster “alerts”, considering that many weather-based disruptions grant an “alert” thanks to weather forecast