DELL'AMICO M.

Social networks are usually navigable small worlds: individuals are able to find short chains of acquaintances connecting pairs of unrelated nodes. This property can be explained by the fact that nodes are characterized by a series of properties, such as geographical position, work or educational background; the navigation proceeds towards the...

Reputation in P2P networks is an important tool to encourage cooperation among peers. It is based on ranking of peers according to their past behaviour. In large-scale real world networks, a global centralised knowledge about all nodes is neither affordable nor practical. For this reason, reputation ranking is often based on local history...

How to decide whether to engage in transactions with strangers? Whether we're offering a ride, renting a room or apartment, buying or selling items, or even lending money, we need a degree of trust that the others will behave as they should. Systems like Airbnb, Uber, Blablacar, eBay and others handle this by creating systems where people...

Reputation in P2P networks is an important tool to encourage cooperation among peers. It is based on ranking of peers according to their past behaviour. In large-scale real-world networks, a global centralized knowledge about all nodes is neither affordable nor practical. For this reason, reputation ranking is often based on local history...

Modern password guessing attacks adopt sophisticated probabilistic techniques that allow for orders of magnitude less guesses to succeed compared to brute force. Unfortunately, best practices and password strength evaluators failed to keep up: they are generally based on heuristic rules designed to defend against obsolete brute force attacks....

Digital content production and distribution has radically changed our business models. An unprecedented volume of supply is now on offer, whetted by the demand of millions of users from all over the world. Since users cannot be expected to browse through millions of different items to find what they might like, filtering has become a popular...

Digital content production and distribution has radically changed our business models. An unprecedented volume of supply is now on offer, whetted by the demand of millions of users from all over the world. Since users cannot be expected to browse through millions of different items to find what they might like, filtering has become a popular...

Size-based scheduling with aging has been recognized as an effective approach to guarantee fairness and near-optimal system response times. We present HFSP, a scheduler introducing this technique to a real, multi-server, complex, and widely used system such as Hadoop. Size-based scheduling requires a priori job size information, which is not...

User connectivity patterns in network applications are known to be heterogeneous and to follow periodic (daily and weekly) patterns. In many cases, the regularity and the correlation of those patterns is problematic: For network applications, many connected users create peaks of demand; in contrast, in peer-to-peer scenarios, having few users...

We study size-based schedulers, and focus on the impact of inaccurate job size information on response time and fairness. Our intent is to revisit previous results, which allude to performance degradation for even small errors on job size estimates, thus limiting the applicability of size-based schedulers. We show that scheduling performance is...

In Peer-to-Peer storage and backup applications, large amounts of data have to be transferred between nodes. In general, recipient of data transfers are not chosen randomly from the whole set of nodes in the Peer-to-Peer networks, but they are chosen according to peer selection rules imposing several criteria, such as resource contributions,...

In this work we study the benefits of a peer-assisted approach to online backup applications, in which spare bandwidth and storage space of end-hosts complement that of an online storage service. Via simulations, we analyze the interplay between two key aspects of such applications: data placement and bandwidth allocation. Our analysis focuses...

This work introduces a new task preemption primitive for Hadoop, that allows tasks to be suspended and resumed exploiting existing memory management mechanisms readily available in modern operating systems. Our technique fills the gap that exists between the two extreme cases of killing tasks (which waste work) or waiting for their completion...

Fuzzy hashing algorithms provide a convenient way of summarizing in a compact form the content of files, and of looking for similarities between them. Because of this, they are widely used in the security and forensics communities to look for similarities between binary program files; one version of them, ssdeep, is the de facto standard to...

It is a well known fact that user-chosen passwords are somewhat predictable: by using tools such as dictionaries or probabilistic models, attackers and password recovery tools can drastically reduce the number of attempts needed to guess a password. Quite surprisingly, however, existing literature does not provide a satisfying answer to the...

The current evolution of the cyber-threat ecosystem shows that no system can be considered invulnerable. It is therefore important to quantify the risk level within a system and devise risk prediction methods such that proactive measures can be taken to reduce the damage of cyber attacks. We present RiskTeller, a system that analyzes binary...

Size-based schedulers have very desirable performance properties: optimal or near-optimal response time can be coupled with strong fairness. Despite this, however, such systems are rarely implemented in practical settings, because they require knowing a priori the amount of work needed to complete jobs: this assumption is difficult to satisfy...

Skype is one of the most used P2P applications on the Internet: VoIP calls, instant messaging, SMS and other features are provided at a low cost to millions of users. Although Skype is a closed source application, an API allows developers to build custom plugins which interact over the Skype network, taking advantage of its reliability and...

Size-based scheduling with aging has, for long, been recognized as an effective approach to guarantee fairness and near-optimal system response times. We present HFSP, a scheduler introducing this technique to a real, multi-server, complex and widely used system such as Hadoop. Size-based scheduling requires a priori job size information, which...

We define and explore the design space of efficient algorithms to compute ROLLUP aggregates, using the MapReduce programming paradigm. Using a modeling approach, we explain the non-trivial trade-o. that exists between parallelism and communication costs that is inherent to a MapReduce implementation of ROLLUP. Furthermore, we design a new...

We propose a redundancy management mechanism for peer-to-peer backup applications. Since, in a backup system, data is read over the network only during restore processes caused by data loss, redundancy management targets data durability rather than attempting to make each piece of information availabile at any time. Each peer determines, in an...

We present NG-DBSCAN, an approximate density-based clustering algorithm that operates on arbitrary data and any symmetric distance measure. The distributed design of our algorithm makes it scalable to very large datasets; its approximate nature makes it fast, yet capable of producing high quality clustering results. We provide a detailed...