A HOLISTIC REDUNDANCY- AND INCENTIVE-BASED FRAMEWORK TO IMPROVE CONTENT AVAILABILITY IN PEER-TO-PEER NETWORKS

Peer-to-Peer (P2P) technology has emerged as an important alternative to the traditional client-server communication paradigm to build large-scale distributed systems. P2P enables the creation, dissemination and access to information at low cost and without the need of dedicated coordinating entities. However, existing P2P systems fail to provide high-levels of content availability, which limit their applicability and adoption. This dissertation takes a holistic approach to device mechanisms to improve content availability in large-scale P2P systems. Content availability in P2P can be impacted by hardware failures and churn. Hardware failures, in the form of disk or node failures, render information inaccessible. Churn, an inherent property of P2P, is the collective effect of the users’ uncoordinated behavior, which occurs when a large percentage of nodes join and leave frequently. Such a behavior reduces content availability significantly. Mitigating the combined effect of hardware failures and churn on content availability in P2P requires new and innovative solutions that go beyond those applied in existing distributed systems. To addresses this challenge, the thesis proposes two complementary, low cost mechanisms, whereby nodes self-organize to overcome failures and improve content availability. The first mechanism is a low complexity and highly flexible hybrid redundancy scheme, referred to as Proactive Repair (PR). The second mechanism is an incentive-based scheme that promotes cooperation and enforces fair exchange of resources among peers. These mechanisms provide the basis for the development of distributed self-organizing algorithms to automate PR and, through incentives, maximize their effectiveness in realistic P2P environments. Our proposed solution is evaluated using a combination of analytical and experimental methods. The analytical models are developed to determine the availability and repair cost properties of PR. The results indicate that PR’s repair cost outperforms other redundancy schemes. The experimental analysis was carried out using simulation and the development of a testbed. The simulation results confirm that PR improves content availability in P2P. The proposed mechanisms are implemented and tested using a DHT-based P2P application environment. The experimental results indicate that the incentive-based mechanism can promote fair exchange of resources and limits the impact of uncooperative behaviors such as “free-riding”

Cross-layer Peer-to-Peer Computing in Mobile Ad Hoc Networks

The future information society is expected to rely heavily on wireless technology. Mobile access to the Internet is steadily gaining ground, and could easily end up exceeding the number of connections from the fixed infrastructure. Picking just one example, ad hoc networking is a new paradigm of wireless communication for mobile devices. Initially, ad hoc networking targeted at military applications as well as stretching the access to the Internet beyond one wireless hop. As a matter of fact, it is now expected to be employed in a variety of civilian applications. For this reason, the issue of how to make these systems working efficiently keeps the ad hoc research community active on topics ranging from wireless technologies to networking and application systems. In contrast to traditional wire-line and wireless networks, ad hoc networks are expected to operate in an environment in which some or all the nodes are mobile, and might suddenly disappear from, or show up in, the network. The lack of any centralized point, leads to the necessity of distributing application services and responsibilities to all available nodes in the network, making the task of developing and deploying application a hard task, and highlighting the necessity of suitable middleware platforms. This thesis studies the properties and performance of peer-to-peer overlay management algorithms, employing them as communication layers in data sharing oriented middleware platforms. The work primarily develops from the observation that efficient overlays have to be aware of the physical network topology, in order to reduce (or avoid) negative impacts of application layer traffic on the network functioning. We argue that cross-layer cooperation between overlay management algorithms and the underlying layer-3 status and protocols, represents a viable alternative to engineer effective decentralized communication layers, or eventually re-engineer existing ones to foster the interconnection of ad hoc networks with Internet infrastructures. The presented approach is twofold. Firstly, we present an innovative network stack component that supports, at an OS level, the realization of cross-layer protocol interactions. Secondly, we exploit cross-layering to optimize overlay management algorithms in unstructured, structured, and publish/subscribe platforms

Passive traffic characterization and analysis in heterogeneous IP networks

In this thesis we revisit a handful of well-known experiments, using modern tools, to see if results yielded from earlier experiments are valid for today’s heterogeneous networks. The traffic properties we look at are relevant for designing and optimizing network equipment, such as routers and switches, and when building corporate networks. We have looked at the characteristics of two different heterogeneous networks; a university network, and an ISP network. We have captured traffic from different weeks, and at different times of the day. We first describe the challenges involved with collecting, processing and analyzing traffic traces from high-speed networks. Then we then look at the various factors that contribute to uncertainty in such measurements, and we try to deduct these factors. The experiments involve collection and analysis of high-resolution traffic traces fromtwo operative networks, each ofwhich contains several gigabytes of network traffic data. We look at properties such as: Packet inter-arrival time distributions, packet size distributions, modeling packet arrivals (self-similarity versus Poisson), traffic per application (egress traffic per destination port), and protocol distributions. A simplistic attempt to quantify the volume of Peer-to-Peer (P2P) traffic inspecting both header data and payload is conducted to evaluate the efficiency of today’s methodology for identification (port numbers only). We have used freely available tools like TCPDump, Ethereal, TEthereal, Ntop, and especially the CAIDA CoralReef suite. The shortcomings of these tools for particular tasks have been compensated for by writing custom-made Perl scripts, proving that it is possible to do advanced analysis with fairly simple means. Our results reveal that there are in fact measurable differences in terms of packet inter-arrival time distributions and statistical properties in the two networks. We also find significant differences in the application distribution, and the deployment of new technologies such as Multicast.Master i nettverks- og systemadministrasjo

A Content Delivery Model for Online Video

Online video accounts for a large and growing portion of all Internet traffic. In order to cut bandwidth costs, it is necessary to use the available bandwidth of users to offload video downloads. Assuming that users can only keep and distribute one video at any given time, it is necessary to determine the global user cache distribution with the goal of achieving maximum peer traffic. The system model contains three different parties: viewers, idlers and servers. Viewers are those peers who are currently viewing a video. Idlers are those peers who are currently not viewing a video but are available to upload to others. Finally, servers can upload any video to any user and has infinite capacity. Every video maintains a first-in-first-out viewer queue which contains all the viewers for that video. Each viewer downloads from the peer that arrived before it, with the earliest arriving peer downloading from the server. Thus, the server must upload to one peer whenever the viewer queue is not empty. The aim of the idlers is to act as a server for a particular video, thereby eliminating all server traffic for that video. By using the popularity of videos, the number of idlers and some assumptions on the viewer arrival process, the optimal global video distribution in the user caches can be determined