Sebastian Kaune

A Trace-Driven Analysis of Caching in Content-Centric Networks

A content-centric network is one which supports host-to-content routing, rather than the host-to-host routing of the existing Internet. This paper investigates the potential of caching data at the router-level in content-centric networks. To achieve this, two measurement sets are combined to gain an understanding of the potential caching benefits of deploying content-centric protocols over the current Internet topology. The first set of measurements is a study of the BitTorrent network, which provides detailed traces of content request patterns. This is then combined with CAIDAs ITDK Internet traces to replay the content requests over a real-world topology. Using this data, simulations are performed to measure how effective content-centric networking would have been if it were available to these consumers/providers. We find that larger cache sizes (10,000 packets) can create significant reductions in packet path lengths. On average, 2.02 hops are saved through caching (a 20% reduction), whilst also allowing 11% of data requests to be maintained within the requesters AS. Importantly, we also show that these benefits extend significantly beyond that of edge caching by allowing transit ASes to also reduce traffic.

Is content publishing in BitTorrent altruistic or profit-driven?

BitTorrent is the most popular P2P content delivery application where individual users share various type of content with tens of thousands of other users. The growing popularity of BitTorrent is primarily due to the availability of valuable content without any cost for the consumers. However, apart from required resources, publishing (sharing) valuable (and often copyrighted) content has serious legal implications for users who publish the material (or publishers). This raises a question that whether (at least major) content publishers behave in an altruistic fashion or have other incentives such as financial. In this study, we identify the content publishers of more than 55K torrents in two major BitTorrent portals and examine their behavior. We demonstrate that a small fraction of publishers is responsible for 67% of the published content and 75% of the downloads. Our investigations reveal that these major publishers respond to two different profiles. On the one hand, antipiracy agencies and malicious publishers publish a large amount of fake files to protect copyrighted content and spread malware respectively. On the other hand, content publishing in BitTorrent is largely driven by companies with financial incentives. Therefore, if these companies lose their interest or are unable to publish content, BitTorrent traffic/portals may disappear or at least their associated traffic will be significantly reduced.

Modelling the Internet Delay Space Based on Geographical Locations

Existing approaches for modelling the Internet delay space predict end-to-end delays between two arbitrary hosts as static values. Further, they do not capture the characteristics caused by geographical constraints. Peer-to-peer (P2P) systems are, however, often very sensitive to the underlying delay characteristics of the Internet, since these characteristics directly influence system performance. This work proposes a model to predict lifelike delays between a given pair of end hosts. In addition to its low delay computation time, it has only linear memory costs which allows large scale P2P simulations to be performed. The model includes realistic delay jitter, subject to the geographical position of the sender and the receiver. Our analysis, using existing Internet measurement studies reveals that our approach seems to be an optimal tradeoff between a number of conflicting properties of existing approaches.

Unraveling BitTorrent's File Unavailability: Measurements and Analysis

BitTorrent suffers from one fundamental problem: the long-term availability of content. This occurs on a massive-scale with 38% of torrents becoming unavailable within the first month. In this paper we explore this problem by performing two large-scale measurement studies including 46K torrents and 29M users. The studies go significantly beyond any previous work by combining per-node, per-torrent and system-wide observations to ascertain the causes, characteristics and repercussions of file unavailability. The study confirms the conclusion from previous works that seeders have a significant impact on both performance and availability. However, we also present some crucial new findings: (i) the presence of seeders is not the sole factor involved in file availability, (ii) 23.5% of nodes that operate in seedless torrents can finish their downloads, and (iii) BitTorrent availability is discontinuous, operating in cycles of temporary unavailability.

Enabling resilient P2P video streaming: survey and analysis

Peer-to-Peer (P2P) techniques for multimedia streaming have been shown to be a good enhancement to the traditional client/server methods when trying to reduce costs and increase robustness. Due to the fact that P2P systems are highly dynamic, the main challenge that has to be addressed remains supporting the general resilience of the system. Various challenges arise when building a resilient P2P streaming system, such as network failures and system dynamics. In this paper, we first classify the different challenges that face P2P streaming and then present and analyze the possible countermeasures. We classify resilience mechanisms as either core mechanisms, which are part of the system, or as cross-layer mechanisms that use information from different communication layers, which might inflict additional costs. We analyze and present resilience mechanisms from an engineering point of view, such that a system engineer can use our analysis as a guide to build a resilient P2P streaming system with different mechanisms and for various application scenarios.

Load balancing for multimedia streaming in heterogeneous peer-to-peer systems

Multimedia streaming of mostly user generated content is an ongoing trend, not only since the upcoming of Last.fm and YouTube. A distributed decentralized multimedia streaming architecture can spread the (traffic) costs to the user nodes, but requires to provide for load balancing and consider the heterogeneity of the participating nodes. We propose a DHT-based information gathering and analyzing architecture which controls the streaming request assignment in the system and thoroughly evaluate it in comparison to a distributed stateless strategy. We evaluated the impact of the key parameters in the allocation function which considers the capabilities of the nodes and their contribution to the system. Identifying the quality-bandwidth tradeoffs of the information gathering system, we show that with our proposed system a 53% better load balancing can be reached and the efficiency of the system is significantly improved.

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.

Towards Benchmarking of Structured Peer-to-Peer Overlays for Network Virtual Environments

Network virtual environments (NVE) are an evolving trend combining millions of users in an interactive community. A distributed NVE platform promises to lower the administration costs and to benefit from research done in the peer-to-peer (p2p) domain. In order to reuse existing mature p2p overlays for NVEs, a comparative evaluation has to be done in the same environment (e.g. resources of peers, peer behavior, churn, etc.), using appropriate test cases (scenarios) and observing relevant performance metrics. In this paper we present a benchmarking approach for p2p overlays in the context of NVEs. We define related quality attributes, scenarios, and metrics and use them to evaluate Chord and Kademlia as most popular p2p overlays and assess their suitability to NVE.

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.

Juno: A Middleware Platform for Supporting Delivery-Centric Applications

This article proposes a new delivery-centric abstraction which extends the existing content-centric networking API. A delivery-centric abstraction allows applications to generate content requests agnostic to location or protocol, with the additional ability to stipulate high-level requirements regarding such things as performance, security, and resource consumption. Fulfilling these requirements, however, is complex as often the ability of a provider to satisfy requirements will vary between different consumers and over time. Therefore, we argue that it is vital to manage this variance to ensure an application fulfils its needs. To this end, we present the Juno middleware, which implements delivery-centric support using a reconfigurable software architecture to: (i) discover multiple sources of an item of content; (ii) model each source’s ability to provide the content; then (iii) adapt to interact with the source(s) that can best fulfil the application’s requirements. Juno therefore utilizes existing providers in a backwards compatible way, supporting immediate deployment. This article evaluates Juno using Emulab to validate its ability to adapt to its environment.