Sampling cluster endurance for peer-to-peer based content distribution networks

Several types of Content Distribution Networks are being deployed over the Internet today, based on different architectures to meet their requirements (e.g., scalability, efficiency and resiliency). Peer-to-peer (P2P) based Content Distribution Networks are promising approaches that have several advantages. Structured P2P networks, for instance, take a proactive approach and provide efficient routing mechanisms. Nevertheless, their maintenance can increase considerably in highly dynamic P2P environments. In order to address this issue, a two-tier architecture called Omicron that combines a structured overlay network with a clustering mechanism is suggested in a hybrid scheme. In this paper, we examine several sampling algorithms utilized in the aforementioned hybrid network that collect local information in order to apply a selective join procedure. Additionally, we apply the sampling algorithms on Chord in order to evaluate sampling as a general information gathering mechanism. The algorithms are based mostly on random walks inside the overlay networks. The aim of the selective join procedure is to provide a well balanced and stable overlay infrastructure that can easily overcome the unreliable behavior of the autonomous peers that constitute the network. The sampling algorithms are evaluated using simulation experiments as well as probabilistic analysis where several properties related to the graph structure are reveale

Sampling cluster endurance for peer-to-peer based content distribution networks

Several types of Content Distribution Networks are being deployed over the Internet today, based on different architectures to meet their requirements (e.g., scalability, efficiency and resiliency). Peer-to-peer (P2P) based Content Distribution Networks are promising approaches that have several advantages. Structured P2P networks, for instance, take a proactive approach and provide efficient routing mechanisms. Nevertheless, their maintenance can increase considerably in highly dynamic P2P environments. In order to address this issue, a two-tier architecture called Omicron that combines a structured overlay network with a clustering mechanism is suggested in a hybrid scheme. In this paper, we examine several sampling algorithms utilized in the aforementioned hybrid network that collect local information in order to apply a selective join procedure. Additionally, we apply the sampling algorithms on Chord in order to evaluate sampling as a general information gathering mechanism. The algorithms are based mostly on random walks inside the overlay networks. The aim of the selective join procedure is to provide a well balanced and stable overlay infrastructure that can easily overcome the unreliable behavior of the autonomous peers that constitute the network. The sampling algorithms are evaluated using simulation experiments as well as probabilistic analysis where several properties related to the graph structure are reveale

Asymmetric Incentives in Peer-to-Peer Systems

In most application scenarios for Peer-to-Peer systems, in order to achieve an overall acceptable system performance an incentive scheme is required that motivates users to share as much as possible of their free resources Today most peers use connections of asymmetric links, such as A-DSL or cable modems. Therefore, users have significantly more download bandwidth than their available upload bandwidth. Applying this observation to incentive schemes suggests that one unit of upload bandwidth should be valued higher than one download unit. Using such an incentive scheme leads the economy of the system to inflation. The incentive scheme would finally collapse. However, by exhibiting the phenomenon of altruistic behavior altruistic peers would accumulate the waste amount of the incentive units. Thus, inflation might be avoided. Gathering the results of a detailed simulative approach, this paper shows how to balance asymmetric incentive schemes in order to avoid inflation

Does Proactive Secret Sharing Perform in Peer-to-Peer Systems?

Trustworthy applications in fully decentralized systems require a trust anchor. This paper describes how such an anchor can be implemented efficiently in p2p systems. The basic concept is to use threshold cryptography in order to sign messages by a quorum of peers. The focus is put on advanced mechanisms to secure the shares of the secret key over time, using proactive secret sharing. This mechanism was researched in context of the token-based accounting scheme

Fuzzynet: Zero-maintenance Ringless Overlay

Many structured overlay networks rely on a ring invariant as a core network connectivity element. The responsibility ranges of the participating peers and navigability principles (greedy routing) heavily depend on the ring structure. For correctness guarantees, each node needs to eagerly maintain its immediate neighboring links - the ring invariant. However, the ring maintenance is an expensive task and it may not even be possible to maintain the ring invariant continuously under high churn, particularly as the network size grows. Furthermore, routing anomalies in the network, peers behind firewalls and Network Address Translators (NATs) create non-transitivity effects, which inevitably lead to the violation of the ring invariant. We argue that reliance on the ring structure is a serious impediment for real life deployment and scalability of structured overlays. In this paper we propose an overlay called Fuzzynet, which does not rely on the ring invariant, yet have all the functionalities of structured overlays. Fuzzynet takes the idea of lazy overlay maintenance further by dropping any explicit connectivity and data maintenance requirement, relying merely on the actions performed when new Fuzzynet peers join the network. We show that with sufficient amount of neighbors (O(logN), comparable to traditional structured overlays), even under high churn, data can be retrieved in Fuzzynet w.h.p. We validate our novel design principles by simulations as well as PlanetLab experiments and compare it with ring based overlays

Overlay network mechanisms for peer-to-peer systems

The Peer-to-Peer (P2P) paradigm provides an alternative design approach for distributed systems, which relaxes the requirement for dedicated service providers as it is the case in client-server systems. The P2P approach explores the potential to create distributed systems based on the resources and the services that can be provided by any end-point device connected to a common communication medium, i.e. the Internet. P2P-based distributed systems develop dedicated virtual networks on top of physical telecommunication networks, the so-called overlay networks. An overlay network is a mandatory abstraction from physical networks to both flexibly fulfill functional requirements such as connectivity maintenance, indexing and routing, as well as to satisfy non-functional ones, such as scalability, fault-tolerance and load-balance. A challenging aspect in designing overlay networks is the satisfaction of the posed requirements, while coping with potential conflicts among them in a customizable way. This thesis investigates a novel architecture for designing effective overlay networks for P2P systems that considers the most important characteristics of widely deployed systems. In particular, the large number of participants is considered, which introduces network scalability and expandability issues. Moreover, the thesis is concerned with their uncontrollable and difficult to predict behavior, which causes highly dynamic and fluctuating overlay network topologies. Such behavior makes it challenging to design resilient and stable systems that can operate effectively with minimum maintenance cost. Additionally, an important consideration is the intrinsic heterogeneity of their physical capabilities and user behavior that aggravates the problem of even workload distribution. A number of mechanisms have been devised to meet the aforementioned requirements. Starting with the network topology, the usage of de Bruijn graphs is proposed. Their attractive characteristic of having a logarithmically increasing diameter, even when nodes have fixed degree, is particularly useful to address the scalability requirement with minimum maintenance cost. However, the exponential expandability is an intrinsic issue for de Bruijn graphs. A graph construction algorithm based only on local information has been proposed to define de Bruijn variants with incremental expandability properties. Moreover, the fixed node degree (preferably as small as possible to keep the graph maintenance costs low) poses resiliency concerns. This matter is addressed with the introduction of peer clusters that guarantee their reliability and with a two-tier topology where the de Bruijn structure applies at the inter-cluster connections. This hybrid topology provides a tightly structured network. In parallel, it gives the freedom of selecting neighbor peers from several members of the neighbor clusters. This selection can be driven by various policies and metrics, i.e., by the efficient mapping to the underlying network or by satisfying trust-level requirements. Additional mechanisms have been proposed for the intra-cluster organization that deals with peer heterogeneity. For this issue, a role-based approach has been investigated. The common, basic operations of P2P overlay networks have been identified assigning a role to each of them. More specifically, four core roles have been identified: Routers, Cachers, Indexers and Maintainers. Peers are assigned with roles based on their capabilities and their predicted behavior so that each peer can contribute in an efficient way without hindering and degrading the overall performance. Certain rules increase the balanced contribution of each peer resulting in a fair solution. The proposed architecture has been realized within the Omicron approach. The resulting system has been evaluated both analytically and by simulation. The analytical approach is based on stochastic modeling, analysis and evaluation of the mechanisms that take into account empirically observed measurements collected from widely deployed P2P systems. Further, burn-in methods that capitalize on conditional reliability approaches are utilized in order to provide an optimal role assignment decision. The simulative approach required the usage of a tool capable of accurately capturing the dynamics of user behavior, the characteristics of the underlying networks and the detailed interaction of the involved P2P protocols. An open architecture simulation framework has been developed to augment the evaluation of our work as well as other important alternative solutions. Thereby, comparative quantitative measures of the performance in a wide range of interesting scenarios are provided. Both the analytical and the simulation results demonstrate the superior design of Omicron for large scale, dynamic and heterogeneous environments as well as its ability to effectively adapt a plethora of trade-offs in requirement constraint

COSMOS: Collaborative system framework based on MPEG-4 objects and streams.

In this thesis, a new collaborative framework has been developed, based on the specifications of the MPEG-4 standard. The framework provides access to the content of the scene, which is constructed in a directed acyclic graph. The scene is compressed and streamed using the MPEG-4 Binary Format for Scene (BIFS) specifications. In addition, VRML files are supported and translated to BIFS. The rendering of the scene is based on Java 3D. Media streams like audio and video are also rendered in the same scene with the 3D content. They can be rendered in the surface of every shape. The Java Media Framework (JMF) is used to decode and encode the audio-visual streams, and it is extended to enable their rendering in the 3D scene. The transmission of the media streams among the participants of the shared environment is over the RTP protocol, using multicast delivery. JMF provides an implementation of the RTP protocol. This implementation is extended to provide a reliable multicast transmission protocol for the exchange of critical content, like the BIFS stream. (Abstract shortened by UMI.

Using DMIF for abstracting from IP-telephony signaling protocols

IP Telephony recently finds a lot of attention and will be used in IP based networks and in combination with the existing conventional telephone system. There is a multitude of competing signaling protocol standards, interfaces and implementation approaches. A number of basic functions can be found throughout all of those, though. This includes the addressing of participants using symbolic names, the negotiation of connections and their parameters as well as the enforcement of a dedicated handling of data streams by means of QoS signaling activities. Thus, a generic abstraction hiding underlying protocol specifics is very desirable and useful. The Delivery Multimedia Integration Framework DMIF - as part of the MPEG approach towards distributed multimedia systems - forms a general and comprehensive framework that is applicable to a wide variety of multimedia scenarios. In this paper we describe a more generalized and abstract view to basic IP Telephony signaling functions and show how these can be hidden below a common DMIF interface. This will allow for the implementation of inter-operable applications and a concentration on communication functionality rather than protocol details. We expect that this will also allow for better exchangeability, interoperability and deployability of emerging signaling extensions

Sampling Cluster Endurance for Peer-to-Peer based Content Distribution Networks.

Several types of Content Distribution Networks are being deployed over the Internet today, based on different architectures to meet their requirements (e.g., scalability, efficiency and resiliency). Peer-to-peer (P2P) based Content Distribution Networks are promising approaches that have several advantages. Structured P2P networks, for instance, take a proactive approach and provide efficient routing mechanisms. Nevertheless, their maintenance can increase considerably in highly dynamic P2P environments. In order to address this issue, a two-tier architecture called Omicron that combines a structured overlay network with a clustering mechanism is suggested in a hybrid scheme. In this paper, we examine several sampling algorithms utilized in the aforementioned hybrid network that collect local information in order to apply a selective join procedure. Additionally, we apply the sampling algorithms on Chord in order to evaluate sampling as a general information gathering mechanism. The algorithms are based mostly on random walks inside the overlay networks. The aim of the selective join procedure is to provide a well balanced and stable overlay infrastructure that can easily overcome the unreliable behavior of the autonomous peers that constitute the network. The sampling algorithms are evaluated using simulation experiments as well as probabilistic analysis where several properties related to the graph structure are revealed