Eleni Mykoniati

A Sybilproof Indirect Reciprocity Mechanism for Peer-to-Peer Networks

Although direct reciprocity (Tit-for-Tat )c ontribu- tion systems have been successful in reducing freeloading in peer- to-peer overlays, it has been shown that, unless the contribution network is dense, they tend to be slow (or may even fail) to converge (1). On the other hand, current indirect reciprocity mechanisms based on reputation systems tend to be susceptible to sybil attacks, peer slander and whitewashing. In this paper we present PledgeRoute, an accounting mech- anism for peer contributions that is based on social capital. This mechanism allows peers to contribute resources to one set of peers and use this contribution to obtain services from a different set of peers, at a different time. PledgeRoute is completely decentralised, can be implemented in both structured and unstructured peer-to-peer systems, and it is resistant to the three kinds of attacks mentioned above. To achieve this, we model contribution transitivity as a routing problem in the contribution network of the peer-to-peer overlay, and we present arguments for the routing behaviour and the sybilproofness of our contribution transfer procedures on this basis. Additionally, we present mechanisms for the seeding of the contribution network, and a combination of incentive mechanisms and reciprocation policies that motivate peers to adhere to the protocol and maximise their service contributions to the overlay.

A Framework for End-to-End Service Differentiation: Network Planes and Parallel Internets

This article presents a technology-agnostic and a multi-dimensional (i.e., routing, forwarding, and traffic management dimensions) approach for the management of IP network resources to ensure service differentiation with both intra- and inter-domain scope. This article introduces the network plane (NP) and parallel Internets (PI) concepts for achieving service differentiation. Based on these concepts, a functional architecture together with a business model is presented. In addition, this article describes how the proposed approach can become a promising platform for the IP multimedia subsystem (IMS), with the objective of providing end-to-end QoS-enabled multimedia delivery across multiple providers to replace the flow-based reservation mode known as the VoIP resource reservation framework.

Scalable peer-to-peer streaming for live entertainment content

We present a system for streaming live entertainment content over the Internet originating from a single source to a scalable number of consumers without resorting to centralized or provider-provisioned resources. The system creates a peer-to-peer overlay network, which attempts to optimize use of existing capacity to ensure quality of service, delivering low startup delay and lag in playout of the live content. There are three main aspects of our solution: first, a swarming mechanism that constructs an overlay topology for minimizing propagation delays from the source to end consumers; second, a distributed overlay anycast system that uses a location-based search algorithm for peers to quickly find the closest peers in a given stream; and finally, a novel incentive mechanism that encourages peers to donate capacity even when the user is not actively consuming content.

Measuring the Relationships between Internet Geography and RTT

When designing distributed systems and Internet protocols, designers can benefit from statistical models of the Internet that can be used to estimate their performance. However, it is frequently impossible for these models to include every property of interest. In these cases, model builders have to select a reduced subset of network properties, and the rest will have to be estimated from those available. In this paper we present a technique for the analysis of Internet round trip times (RTT) and its relationship with other geographic and network properties. This technique is applied on a novel dataset comprising ~19 million RTT measurements derived from ~200 million RTT samples between ~54 thousand DNS servers. Our main contribution is an information-theoretical analysis that allows us to determine the amount of information that a given subset of geographic or network variables (such as RTT or great circle distance between geolocated hosts) gives about other variables of interest. We then provide bounds on the error that can be expected when using statistical estimators for the variables of interest based on subsets of other variables.

Distributed Overlay Anycast Tables Using Space Filling Curves

In this paper we present the Distributed Overlay Anycast Table, a structured overlay that implements application-layer anycast, allowing the discovery of the closest host that is a member of a given group. One application is in locality-aware peer-to-peer networks, where peers need to discover low-latency peers participating in the distribution of a particular file or stream. The DOAT makes use of network delay coordinates and a space filling curve to achieve locality-aware routing across the overlay, and Bloom filters to aggregate group identifiers. The solution is designed to optimise both accuracy and query time, which are essential for real-time applications. We simulated DOAT using both random and realistic node distributions. The results show that accuracy is high and query time is low.

Scalable video streaming over P2P networks: A matter of harmony?

In this paper we address the problem of efficient layered video streaming over peer-to-peer networks and we propose a new receiver-driven streaming mechanism. The main design goal of our new layered video requesting policy is to optimize the overall distribution of video streams in terms of reliability and overhead. Since the layered peer-to-peer streaming problem is NP-Hard, we show that the classic approaches widely used in layered P2P streaming systems have some limitations and we propose an optimization technique based on harmony search which aims at increasing the rate of successful data transmissions for the most important video layers, while reducing the protocol overhead and ensuring load balancing among the participating peers. Analytical results have demonstrated that our new requesting policy enhances the streaming of layered video over mesh-based peer-to-peer networks and outperforms classic approaches.

Improving end-to-end QoE via close cooperation between applications and ISPs

In recent years there has been a trend for more user participation in Internet-based services leading to an explosion of user-generated, tailored, and reviewed content and social-networking- based applications. The next generation of applications will continue this trend and be more interactive and distributed, putting the prosumers at the center of a massively multiparticipant communications environment. Furthermore, future networked media environments will be high-quality, multisensory, multi-viewpoint and multistreamed, relying on HD and 3D video. These applications will place unprecedented demands on networks between unpredictable and arbitrarily large meshes of network endpoints. We advocate the development of intelligent cross-layer techniques that, on one hand, will mobilize network and user resources to provide network capacity where it is needed, and, on the other hand, will ensure that the applications adapt themselves and the content they are conveying to available network resources. This article presents an architecture to enable this level of cooperation between the application providers, the users, and the communications networks so that the quality of experience of the users of the application is improved and network traffic optimized.

On the relationship between fundamental measurements in TCP flows

This paper considers fundamental measurements which drive TCP flows: throughput, RTT and loss. It is clear that throughput is, in some sense, a function of both RTT and loss. In their seminal paper Padyhe et al [1] begin with a mathematical model of the TCP sliding window evolution process and come up with an equation showing that TCP throughput is (roughly) proportional to 1/RTT√p where p is the probability of packet loss. Their equation is shown to be consistent with data gathered on several links. This paper takes the opposite approach and analyses a large number of packet traces from well-known sources in order to create a data-driven estimate of the functions which relate TCP, loss and RTT. Regression analysis is used to fit models to connect the quantities. The fitted models show different behaviour from that expected in [1].

Performance of locality-aware topologies for peer-to-peer live streaming

This study is concerned with the effect of overlay network topology on the performance of live streaming peer-to-peer systems. The study focuses on the evaluation of topologies which are aware of the delays experienced between different peers on the network. Metrics are defined which assess the topologies in terms of delay, bandwidth usage and resilience to peer drop-out. Several topology creation algorithms are tested and the metrics are measured in a simple simulation testbed. This gives an assessment of the type of gains, which might be expected from locality awareness in peer-to-peer networks.

Overlay Consolidation of ISP-Provided Preferences

There is growing evidence that mutually beneficial outcomes can be achieved when content distribution overlays and their underlying ISPs collaborate through open interfaces. We further contribute to this body of work by considering consolidated topology construction strategies that integrate the information provided by multiple ISPs. We focus on situations with potentially conflicting, asymmetric preference costs, since these situations are expected to benefit more from the tradeoffs provided by consolidation to produce an overlay topology with desirable global properties. In this paper we develop a generic model for the multi-domain consolidation of ISP preferences expressed as costs for pairwise peer connections, where peers are grouped into clusters based on topology criteria. Using this model, we propose two consolidated topology construction strategies: Shared Cost, designed to provide a tradeoff for preference cost asymmetries, and Low Cost, designed to reduce the overall preference cost that the overlay imposes on all its underlying ISPs. We evaluate these two models through extensive simulations over a wide range of ISP and peer cluster sizes, and we show that preference consolidation can provide ISPs with outcomes more aligned with their preferences than those provided by non-consolidated operation.