arXiv subjects

Stefano Ferretti

Publications and source records attributed to Stefano Ferretti.

59 records · Page 4Linked to original sources

arXiv2013

On the Degree Distribution of Faulty Peer-to-Peer Overlays

This paper presents an analytical framework to model fault-tolerance in unstructured peer-to-peer overlays, represented as complex networks. We define a distributed protocol peers execute for managing the overlay and reacting to node faults. Based on the protocol, evolution equations are defined and manipulated by resorting to generating functions. Obtained outcomes provide insights on the nodes' degree probability distribution. From the study of the degree distribution, it is possible to estimate other important metrics of the peer-to-peer overlay, such as the diameter of the network. We study different networks, characterized by three specific desired degree distributions, i.e. nets with nodes having a fixed desired degree, random graphs and scale-free networks. All these networks are assessed via the analytical tool and simulation as well. Results show that the approach can be factually employed to dynamically tune the average attachment rate at peers so that they maintain their own desired degree and, in general, the desired network topology.

cs.DC↗

arXiv2012

Walking with the Oracle: Efficient Use of Mobile Networks through Location-Awareness

Always Best Packet Switching (ABPS) is a novel approach for wireless communications that enables mobile nodes, equipped with multiple network interface cards (NICs), to dynamically determine the most appropriate NIC to use. Using ABPS, a mobile node can seamlessly switch to a different NIC in order to get better performance, without causing communication interruptions at the application level. To make this possible, NICs are kept always active and a software monitor constantly probes the channels for available access points. While this ensures maximum connection availability, considerable energy may be wasted when no access points are available for a given NIC. In this paper we address this issue by investigating the use of an "oracle" able to provide information on network availability. This allows to dynamically switch on/off NICs based on reported availability, thus reducing the power consumption. We present a Markov model which allows us to estimate the impact of the oracle on the ABPS mechanism: results show that significant reduction in energy consumption can be achieved with minimal impact on connection availability. We conclude by describing a prototype implementation of the oracle based on Web services and geolocalization.

cs.NI↗

arXiv2012

Publish-Subscribe Systems via Gossip: a Study based on Complex Networks

This paper analyzes the adoption of unstructured P2P overlay networks to build publish-subscribe systems. We consider a very simple distributed communication protocol, based on gossip and on the local knowledge each node has about subscriptions made by its neighbours. In particular, upon reception (or generation) of a novel event, a node sends it to those neighbours whose subscriptions match that event. Moreover, the node gossips the event to its "non-interested" neighbours, so that the event can be spread through the overlay. A mathematical analysis is provided to estimate the number of nodes receiving the event, based on the network topology, the amount of subscribers and the gossip probability. These outcomes are compared to those obtained via simulation. Results show even when the amount of subscribers represents a very small (yet non-negligible) portion of network nodes, by tuning the gossip probability the event can percolate through the overlay. Hence, the use of unstructured networks. coupled with simple dissemination protocols, represents a viable approach to build peer-to-peer publish-subscribe applications.

cs.DC↗

arXiv2012

Mitigation of Random Query String DoS via Gossip

This paper presents a mitigation scheme to cope with the random query string Denial of Service (DoS) attack, which is based on a vulnerability of current Content Delivery Networks (CDNs). The attack exploits the fact that edge servers composing a CDN, receiving an HTTP request for a resource with an appended random query string never saw before, ask the origin server for a (novel) copy of the resource. Such characteristics can be employed to take an attack against the origin server by exploiting edge servers. Our strategy adopts a simple gossip protocol executed by edge servers to detect the attack. Based on such a detection, countermeasures can be taken to protect the origin server and the CDN against the attack. We provide simulation results that show the viability of our approach.

cs.CR↗

arXiv2012

Scale-Free Opportunistic Networks: is it Possible?

The coupling of scale-free networks with mobile unstructured networks is certainly unusual. In mobile networks, connections active at a given instant are constrained by the geographical distribution of mobile nodes, and by the limited signal strength of the wireless technology employed to build the ad-hoc overlay. This is in contrast with the presence of hubs, typical of scale-free nets. However, opportunistic (mobile) networks possess the distinctive feature to be delay tolerant; mobile nodes implement a store, carry and forward strategy that permits to disseminate data based on a multi-hop route, which is built in time, when nodes encounter other ones while moving. In this paper, we consider opportunistic networks as evolving graphs where links represent contacts among nodes arising during a (non-instantaneous) time interval. We discuss a strategy to control the way nodes manage contacts and build "opportunistic overlays". Based on such an approach, interesting overlays can be obtained, shaped following given desired topologies, such as scale-free ones.

cs.DC↗