Marco Savi

Evaluation of the Precision-Privacy Tradeoff of Data Perturbation for Smart Metering

Smart grid users and standardization committees require that utilities and third parties collecting metering data employ techniques for limiting the level of precision of the gathered household measurements to a granularity no finer than what is required for providing the expected service. Data aggregation and data perturbation are two such techniques. This paper provides quantitative means to identify a tradeoff between the aggregation set size, the precision on the aggregated measurements, and the privacy level. This is achieved by formally defining an attack to the privacy of an individual user and calculating how much its success probability is reduced by applying data perturbation. Under the assumption of time-correlation of the measurements, colored noise can be used to even further reduce the success probability. The tightness of the analytical results is evaluated by comparing them to experimental data.

Impact of processing costs on service chain placement in network functions virtualization

The Network Functions Virtualization (NFV) paradigm is the most promising technique to help network providers in the reduction of capital and energy costs. The deployment of virtual network functions (VNFs) running on generic x86 hardware allows higher flexibility than the classical middleboxes approach. NFV also reduces the complexity in the deployment of network services through the concept of service chaining, which defines how multiple VNFs can be chained together to provide a specific service. As a drawback, hosting multiple VNFs in the same hardware can lead to scalability issues, especially in the processing-resource sharing. In this paper, we evaluate the impact of two different types of costs that must be taken into account when multiple chained VNFs share the same processing resources: the upscaling costs and the context switching costs. Upscaling costs are incurred by VNFs multi-core implementations, since they suffer a penalty due to the needs of load balancing among cores. Context switching costs arise when multiple VNFs share the same CPU and thus require the loading/saving of their context. We model through an ILP problem the evaluation of such costs and we show their impact in a VNFs consolidation scenario, when the x86 hardware deployed in the network is minimized.

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.

A decisional attack to privacy-friendly data aggregation in Smart Grids

The privacy-preserving management of energy consumption measurements gathered by Smart Meters plays a pivotal role in the Automatic Metering Infrastructure of Smart Grids. Grid users and standardization committees are requiring that utilities and third parties collecting aggregated metering data are prevented from accessing measurements at the household granularity, and data perturbation is a technique used to provide a trade-off between the privacy of individual users and the precision of the aggregated measurements. In this paper, we discuss a decisional attack to aggregation with data-perturbation, showing that a curious entity can exploit the temporal correlation of Smart Grid measurements to detect the presence or absence of individual data generated by a given user inside an aggregate. We also propose a countermeasure to such attack and show its effectiveness using both synthetic and real home energy consumption measurement traces.

Using replicated video servers for VoD traffic offloading in integrated metro/access networks

Internet traffic is increasingly becoming a mediastreaming traffic. Especially, Video-on-Demand (VoD) services are pushing the demand for broadband connectivity to the Internet, and optical fiber technology is being deployed in the access network to keep up with such increasing demand. To provide a more scalable network architecture for video/content delivery, network operators are currently considering novel integrated metro/access networks which accommodate replicated video servers directly in their infrastructure. In such way, servers for VoD delivery are placed nearer to the end users, the core segment of the network is partially traffic offloaded, and the end users experience better performance in terms of QoS. In our work, we will evaluate the performance improvement of an integrated metro/access architecture for VoD delivery with replicated video servers considering different configurations in terms of number of replicated servers, meshing degree and adopted network technologies. We develop a network simulator in which replicas of video servers (called Metro Servers, or MSs) are deployed to meet the demand of VoD traffic. In the result section we compare the performance of the various configurations and discuss which are the minimum requirements to minimize blocking of the VoD requests.

To distribute or not to distribute? Impact of latency on Virtual Network Function distribution at the edge of FMC networks

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.

Energy-efficient caching for Video-on-Demand in Fixed-Mobile Convergent networks

The success of novel bandwidth-consuming multimedia services such as Video-on-Demand (VoD) is leading to a tremendous growth of the Internet traffic. Content caching can help to mitigate such uncontrolled growth by storing video content closer to the users in core, metro and access network nodes. So far, metro and especially access networks supporting mobile and fixed users have evolved independently, leveraging logically (and often also physically) separate infrastructures; this means that mobile users cannot access caches placed in the fixed access network (and vice-versa), even if they are geographically close to them, and energy consumption implications of such undesired effect must be investigated. We define an optimization problem modeling an energy-efficient placement of caches in core, metro and fixed/mobile access nodes of the network. Then, we show how the evolution towards a Fixed-Mobile Converged metro/access network, where fixed and mobile users can share caches, can reduce the energy consumed for VoD content delivery.

Protection strategies for virtual network functions placement and service chains provisioning

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.

ICN based shared caching in future converged fixed and mobile network

The explosion of mobile multimedia and Internet-of-things (IoT) services implies strong requirements for seamless switching among various types of networks. Thus, to offer true ubiquitous Internet connection, a Fixed and Mobile Converged (FMC) network architecture is essential for the future 5G network. Such a convergent network can not only improve the utilization of network resources, but also inspire new add-on services for FMC network operators. In this paper, we introduce a shared caching overlay based on Information Centric Networking (ICN). It is deployed on top of the FMC network and controlled by the FMC network operator to offer Caching as a Service (CaaS) to Over-The-Top (OTT) service providers and virtual network operators. Business analysis and performance evaluation will highlight the benefits of deploying such a controlled Shared Caching System (SCS) over an FMC network.

An Energy-Efficient Strategy for VoD Content Replication in Integrated Metro/Access Networks

The Video-on-Demand (VoD) service is becoming one the most popular Internet services. Due to its bandwidth-consuming nature and thanks to the efforts made by telecom operators to provide the users with higher access rates, an huge amount of VoD traffic is expected to flood the core segment of the network, potentially leading to congestion and Quality of Experience degradation issues. A growing body of research is studying how to alleviate such traffic explosion. One of the most promising solutions consists in migrating the content in the metro and access segments of the network by deploying a system of Metro Servers (MSes) for VoD delivery. This way, the VoD traffic is kept as local as possible and the core network is traffic-offloaded. This paper investigates one of the most prominent risks by adopting this solution: in fact, if not carefully managed, a massive deployment of MSes in the network can lead to a significant increase of the overall energy consumption of the network. We first identify a consistent power model for the MSes and the network equipment in an integrated metro/access architecture scenario, then we define a strategy to switch on and off the network interfaces and the MSes depending on the VoD traffic load variation during the day. We show by means of simulations how our strategy always strikes the best trade-off between the energy consumption for content transport through the network and the energy consumption for processing and storage in the MSes.