Telecom operators worldwide are witnessing squeezed profit margins mainly due to hyper-competition. Hence, new business models/strategies are needed to help operators reduce Operational and Capital Expenditures. In this context, the Network Function Virtualization (NFV) paradigm, which consists of running Virtual Instances of Network Functions (NFs) in Commercial-Off-The-Shelf (COTS) hardware, represents a solid alternative. Virtual Network Functions (VNFs) are then concatenated together in a sequential order to form service chains (SCs) that provide specific Internet services. In this article, we study different approaches to provision SCs with resiliency against single-link and single-node failures. We propose three Integer Linear Programming (ILP) models to jointly solve the problem of VNF placement and traffic routing, while guaranteeing resiliency against single-link and/or single-node failures. Specifically, we focus on the trade-off between the conflicting objectives of meeting SCs latency requirements and consolidating as many as possible VNFs in NFV-capable nodes. We show that providing resiliency against both singlelink and single-node failures comes at twice the amount of resources in terms of NFV-capable 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-node failures. Finally, we discuss important insights about the deployment of bandwidth-intensive SCs. System (IDPS), etc.) 1 within the network [21]. From the cost point of view, telecom operators are witnessing a decrease of the revenue-per-bit, which is envisioned to be even lower than the cost-per-bit, due to the competition from Over-The-Tops (OTTs). The applications introduced by OTTs (e.g., Voice-over-IP (VoIP)) leave the Internet Service Provider (ISP) responsible for only transporting the information, hence contributing heavily in their revenue decrease. Network Function Virtualization (NFV) is a new architectural paradigm that was proposed to improve the flexibility of network service provisioning and reduce the time to market of new services [14]. NFV can revolutionize how network operators design their infrastructure, by leveraging virtualization, to separate software instances from hardware appliances, and decoupling functionalities from locations for faster service provisioning. NFV supports the instantiation of Virtual Network Functions (VNFs) through software virtualization techniques and runs them on Commercial-Off-The-Shelf (COTS) hardware. Hence, the virtualization of network functions opens the way to the provisioning of new services without the installation of new equipment. It is clear 1 A list of acronyms to ease the reading is presented in the last page of this article.

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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

Telecom operators worldwide are witnessing squeezed profit margins mainly due to hyper‐competition. Hence, new business models/strategies are needed to help operators reduce Operational and Capital Expenditures. In this context, the Network Function Virtualization (NFV) paradigm, which consists of running Virtual Instances of Network Functions (NFs) in Commercial‐Off‐The‐Shelf (COTS) hardware, represents a solid alternative. Virtual Network Functions (VNFs) are then concatenated together in a sequential order to form service chains (SCs) that provide specific Internet services. In this article, we study different approaches to provision SCs with resiliency against single‐link and single‐node failures. We propose three Integer Linear Programming (ILP) models to jointly solve the problem of VNF placement and traffic routing, while guaranteeing resiliency against single‐link and/or single‐node failures. Specifically, we focus on the trade‐off between the conflicting objectives of meeting SCs latency requirements and consolidating as many as possible VNFs in NFV‐capable nodes. We show that providing resiliency against both single‐link and single‐node failures comes at twice the amount of resources in terms of NFV‐capable 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‐node failures. Finally, we discuss important insights about the deployment of bandwidth‐intensive SCs. © 2017 Wiley Periodicals, Inc. NETWORKS, Vol. 70(4), 373–387 2017

The Network Function Virtualization paradigm enables the possibility to dynamically instantiate Virtual Network Functions (VNFs) in Commercial-Off-The-Shelf (COTS) hardware. Such VNFs are then concatenated together in Service Chains (SCs) to provide specific Internet services to the users. Depending on latency requirements for such services and considering the aim of maximally consolidating the VNFs (i.e., of minimizing the COTS hardware), the VNFs can be centralized in few datacenters in the core network or they can be distributed closer to the edge of the network. In this paper we evaluate the impact of latency requirements of SCs on VNF distribution towards the edge of the network, by also showing the benefits of a Fixed and Mobile Convergent (FMC) metro/access network, with respect to a non-convergent network, in terms of consolidation