Nicolas Liebau

Globase.KOM - A P2P Overlay for Fully Retrievable Location-based Search

Location based services are becoming increasingly popular as devices that determine geographical position become more available to end users. The main problem of existing solutions to location-based search is keeping information updated requires centralized maintenance at specific times. Therefore, retrieved results do not include all objects that exist in reality. A peer-to-peer (P2P) approach can easily overcome this issue as peers are responsible for the information users are searching for. Unfortunately, current state-of-the-art overlays cannot fulfill the requirements for efficient and fully retrievable location-based search. In this paper we present Globase.KOM, a hierarchical tree-based P2P overlay that enables fully retrievable location-based overlay operations which proved to be highly efficient and logarithmically scalable.

Token-based accounting and distributed pricing to introduce market mechanisms in a peer-to-peer file sharing scenario

We present a token-based accounting mechanism that alleviates the free riding problem in P2P networks. The approach is complemented by distributed pricing as a flexible and viable scheme to incite users to share valuable content and to efficiently balance requests among all peers based on economic decisions.

Token-based Accounting for P2P-Systems

This paper presents a token-based accounting scheme for decentralized autonomous systems, such as peer-to-peer systems. The scheme uses tokens as proof of resource or service usage. Conforming to the peer-to-peer paradigm, the tokens are issued using a decentralized mechanism. Within peer-to-peer systems the proposed accounting scheme can be used to overcome information deficits. Thus, it constitutes the basis for coordination and control mechanisms as well as for pricing in commercial scenarios in fully decentralized systems. The presented scheme is compared against an alterative approach showing the advantage of the token-based scheme in terms of communication costs.

Overlay Bandwidth Management: Scheduling and Active Queue Management of Overlay Flows

Peer-to-peer and mobile networks gained significant attention of both research community and industry. Applying the peer-to-peer paradigm in mobile networks lead to several problems regarding the bandwidth demand of peer-to-peer networks. Time-critical messages are delayed and delivered unacceptably slow. In addition to this, scarce bandwidth is wasted on messages of less priority. Therefore, the focus of this paper is on bandwidth management issues at the overlay layer and how they can be solved. We present HiPNOS.KOM, a priority based scheduling and active queue management system. It guarantees better QoS for higher prioritized messages in upper network layers of peer-to-peer systems. Evaluation using the peer-to-peer simulator PeerfactSim. KOM shows that HiPNOS.KOM brings significant improvement in Kademlia in comparison to FIFO and drop-tail, strategies that are used nowadays on each peer. User initiated lookups have in Kademlia 24% smaller operation duration when using HiPNOS.KOM.

Benchmarking Platform for Peer-to-Peer Systems (Benchmarking Plattform für Peer-to-Peer Systeme)

Summary The benefits of the peer-to-peer paradigm have been proven through various applications besides file sharing. The requirements for the design of peer-to-peer overlay networks vary according to its purpose. In order to compare existing overlay networks and determine their suitability for specific purposes, requirements are defined with abstract quality attributes. Once the benchmarking set (quality attribute, metrics, and scenarios) is identified, experiments should be applied under the same circumstances on each overlay in order to obtain comparable results. This paper presents PeerfactSim.KOM, a simulator providing a benchmarking platform for peer-to-peer systems, especially for overlay networks. It supports defined benchmarking sets for all kinds of peer-to-peer overlays through an implemented catalogue of metrics and a simple but comprehensive scenario specification. Various peer distributions and churn rates are given which also supports geographical-location dependence. The platform is extensible due to its modular design and can scale up to around 106; peers for simple overlays such as Gnutella and 105; for more complex overlays like Kademlia. Zusammenfassung In vielen Anwendungen jenseits der Dateitauschbörsen zeigen sich die Vorteile des Peer-to-Peer Kommunikationsparadigmas. Abhängig vom Zweck variieren die Anforderungen an das Design eines geeigneten Peer-to-Peer-Overlay-Netzes. Um existierende Overlay-Netze vergleichen zu können und um zu entscheiden, ob sie für einen festgelegten Zweck geeignet sind, werden die Anforderungen mit abstrakten Qualitätsattributen beschrieben. Hat man einen Benchmarking-Satz (Qualitätsattribute, Metriken und Szenarios) identifiziert, sollte dieser, um vergleichbare Resultate zu erzielen, bei der Messung eines jeden Overlay-Netzes eingesetzt werden. Der Schwerpunkt dieser Arbeit ist Peerfact.KOM, ein Simulator, der eine Benchmarking-Plattform für Peer-to-Peer-Overlay-Netze bereitstellt. Für alle verschiedenen Arten von Peer-to-Peer-Overlay-Netzen bietet er festgelegte Benchmarking-Sätze, einen implementierten Katalog von Metriken und eine einfache, aber ausdrucksstarke Methode, um Szenarien zu spezifizieren. Verschiedene Churn-Raten und Peer-Verteilungen, die optional auch auf geographische Ortsangaben bezogen sind, werden geboten. Der Simulator ist durch sein modulares Design erweiterbar. Er skaliert bis zu 106; Peers in einfachen Overlay-Netzen wie Gnutella und 105; in komplexeren Overlay-Netzen wie Kademlia.

Location Awareness—Improving Distributed Multimedia Communication

Multimedia creation and consumption is highly intensive and makes up the majority of Internet traffic nowadays. End-users are able to share their digital content with each other and to build communities based on interests, which often differ drastically according to location. Distributing these media using a central server can be quite expensive for a content provider. Distributed (peer-to-peer like) systems share costs evenly among participants. Thus, distributed multimedia systems will be more important in the future. The global distribution of end-users aggravates high-quality delivery of multimedia content. In this paper, we argue that geographical location-awareness greatly helps distributed multimedia communication. It increases the quality of multimedia content delivery and at the same time satisfies the growing need for more personalized, location-based services. In this paper, as a proof of concept, we introduce an overlay structure for distributed multimedia systems (and similar systems), which is location-aware and uses the locations of its nodes to optimize node-to-node communication for performance and delay. At the same time, the system enables location-based services.

Charging in peer-to-peer systems based on a token accounting system

Today, Peer-to-Peer applications are predominant on the internet when considered in terms of its traffic consumption. However apart from Skype, their commercial success is still very limited. This is due to the difficulties faced when trying to implement crucial functionality such as accounting and charging without violating the Peer-to-Peer paradigm. A fully decentralized accounting scheme based on tokens was presented by the authors last year. In this paper we analyse the interactions between token-based accounting and charging in order to enable peers to charge for their services. We present three different charging schemes using tokens as (1) pure receipts, as (2) Micropayment, and as (3) bill of exchange. These schemes are evaluated based on the provided security and the overhead traffic introduced into a Peer-to-Peer system.

Peer-to-Peer Systems (Peer-to-Peer-Systeme)

The term peer-to-peer started gaining popularity since summer 2000. This identified a group of applications which allow the clients involved to interact directly as opposed to the well established client/ server approach. These applications include Napster, SETI@home, Freenet, and Gnutella. The peerto-peer communication paradigm involves direct communication and sharing of resources amongst peers, or simply: peer-to-peer. Peer-to-peer applications attracted millions of users in a very short period of time. Napster became one of the fasted growing applications in the history of the Internet. The impact of the peer-topeer paradigm on society, business models and novel Internet technology has been tremendous. Today, about 60% to 80% of the traffic on the Internet stems from applications within the peerto-peer paradigm. The most popular applications are file sharing and content distribution. With the introduction of Skype, Internet telephony has also experienced a significant growth and is often blamed for the falling revenues in the telecommunication industry. VoIP providers were never a serious threat for traditional telecommunication providers, at least until Skype started being used widely. Apart from Skype, peer-to-peer applications have failed to achieve commercial success. Peer-to-peer is a disruptive technology as it does not have a central entity without which companies are unable to generate revenues. This is contrary to traditional business models. It has been proven that peer-to-peer based content distribution is able to cut distribution costs, e. g., by using native BitTorrent, up to 90% of bandwidth costs can be saved compared to client/server delivery. Therefore, many current peer-to-peer based video-on-demand applications, e. g., Babelgum, Joost, or Zattoo, are being developed. From the moment the first peerto-peer applications appeared, the research community has become heavily active in this area. Peer-topeer became a field of research on its own, which combines research in networking, systems, and theory. Every year since 2001, e. g., at the ACM SigComm, one of the most recognized conferences in networking, several papers in the area of peer-to-peer have appeared. Conferences dedicated to peer-to-peer have been established, such as the IEEE P2P-Conference or the International Workshop on Peer-to-Peer Systems. Besides this, all top journals on networking and systems also regularly publish papers on peer-topeer. Peer-to-peer continues to remain very attractive for researchers as (1) central entities should be avoided, (2) traditional straight forward communication patterns between the nodes of the network cannot be applied as self-organization takes place, and (3) peer-to-peer requires autonomy of nodes. Therefore, strategic or opportunistic peer behaviour always has to be taken into account. Peer-to-peer demands new ideas from the researcher, new ways of thinking and the combination of emerging new mechanisms and existing technologies. Very often the goal is to enhance performance and increase efficiency. This unconventional way of thinking in peer-to-peer seems to be very appealing to students and young researchers. The research community has created a substantial knowledge pool which remains a rapidly evolving field. In this special issue we are proud to present papers which cover (to a certain extent) the most important areas in peer-to-peer research. The DFG research unit (DFG Forschergruppe F 733) “Improvement of the Quality of Peer-to-Peer Systems by Systematically Researching Quality Features and Their In-

Accounting in Peer-to-Peer Systems

Today’s Peer-to-Peer (P2P) systems seem to work fine for file sharing applications. Though, is that true for all kinds of applications or is it just true for file sharing of copyright protected content? In the latter case, clear incentives for sharing exist - users download copyright protected media content for free. Even here free riding is a widespread behavior [11]. Therefore, many file sharing systems introduced incentive systems, like the eMule credit system [192] or BitTorrent [320]. Obviously, for legally used Peer-to-Peer file sharing applications giving incentives to users for sharing their resources in a fair manner is an important feature.

A peer-to-peer content distribution network

The distribution of large content files, like videos, over a large number of users is a demanding and costly operation if done using a traditional client/server architecture. Peer-to-peer based file-sharing systems can be used as an alternative for content distribution. The eDonkey file-sharing network is one of the most successful peer-to-peer file-sharing networks, especially in Germany. eDonkey forms a hybrid network that capitalizes both on the client/server and peer-to-peer paradigms in the design of its architecture. In this paper, we describe the eDonkey protocol, the constructed overlay network, the critical operations and their characteristics, as well as the results of measurements of the network and transport layer and of the user behavior. The measurements were made with the client software and with an open-source eDonkey server we extended explicitly for these measurements. Our study shows that eDonkey is particularly well suited for content distribution and not surprisingly also intensively used for the distribution of large files, mainly videos.