Maximilian Michel

Characterization of BitTorrent swarms and their distribution in the Internet

The optimization of overlay traffic resulting from applications such as BitTorrent is a challenge addressed by several recent research initiatives. However, the assessment of such optimization techniques and their performance in the real Internet remains difficult. Despite a considerable set of works measuring real-life BitTorrent swarms, several characteristics of those swarms relevant for the optimization of overlay traffic have not yet been investigated. In this work, we address this lack of realistic swarm statistics by presenting our measurement results. In particular, we provide a statistical characterization of the swarm sizes, the distribution of peers over autonomous systems (ASs), the fraction of peers in the largest AS, and the size of the shared files. To this end, we consider different types of shared content and identify particular characteristics of regional swarms. The selection of the presented data is inspired by ongoing discussions in the IETF working group on application layer traffic optimization (ALTO). Our study is intended to provide input for the design and the assessment of ALTO solutions for BitTorrent, but the applicability of the results is not limited to that purpose.

Can P2P-Users Benefit from Locality-Awareness?

Locality-awareness is considered as a promising approach to increase the efficiency of content distribution by peer-to-peer (P2P) networks, e.g., BitTorrent. It is intended to reduce the inter-domain traffic which is costly for Internet service providers (ISPs) and simultaneously increase the performance from the viewpoint of the P2P users, i.e, shorten download times. This win-win situation should be achieved by a preferred exchange of information between peers which are located closely to each other in the underlying network topology. A set of studies shows that these approaches can lead to a win-win situation under certain conditions, and to a win-no lose situation in most cases. However, the scenarios used assume mostly homogeneous peer distributions and that all peers have the same access speed. This is not the case in practice according to several measurement studies. Therefore, we extend previous work in this paper by studying scenarios with real-life, skewed peer distributions and heterogeneous access bandwidths of peers. We show that even a win-no lose situation is difficult to achieve under those conditions and that the actual impact for a specific peer depends heavily on the used locality-aware peer selection and the concrete scenario. Therefore, we conclude that current proposals need to be refined so that users of P2P networks can be sure that they also benefit from their use. Otherwise, a broad acceptance of the concept of locality-awareness in the user community of P2P networks will not take place.

Towards a Mobile Peer-to-Peer Service Platform

Peer-to-peer (P2P) technology is regarded as being disruptive for traditional fixed and mobile operators. However, it can also be considered as an opportunity for new ways of service provisioning. On the one hand, P2P concepts allow a more efficient usage of existing platform resources through relying on existing infrastructure including even the customer equipment and thus provide a cheap service platform. On the other hand, P2P technology brings new business opportunities through extending the service portfolio to user provided services and to ubiquitous environments. Along these lines, we outline in this paper the requirements and building blocks for a P2P based service platform for mobile environments. In addition to P2P lookup and information distribution, these building blocks include reliability, controllability, bootstrapping, reputation management, which address operator specific requirements in particular. Mobile networks pose severe challenges to a P2P service platform in terms of heterogeneous devices and access connections and frequent user joins and leaves. We present a hierarchical P2P system as a core component for a P2P service platform addressing those problems

Chordella - A Hierarchical Peer-to-Peer Overlay Implementation for Heterogeneous, Mobile Environments

This paper deals with Chordella, a peer-to-peer system that is particularly designed for heterogeneous environments such as in wireless networks. We use a pool of standard personal computers distributed over the Internet which act as reliable nodes and form the backbone of the network as superpeers. The mobile nodes are represented by mobile phones running a lightweight implementation of our system able to use the superpeers as proxies. The demo shows the effectiveness of the approach with a mobile picture sharing application benefiting from several improvements such as load balancing and optimal operation point selection algorithms.

Mitigating unfairness in locality-aware peer-to-peer networks

Locality awareness is considered as a promising approach to increase the efficiency of content distribution by peer-to-peer (P2P) networks, e.g., BitTorrent. It is intended to reduce the inter-domain traffic, which is costly for Internet service providers (ISPs), and to simultaneously increase the performance from the viewpoint of P2P users, i.e., to shorten download times. This win-win situation should be achieved by a preferred exchange of information between peers which are located close to each other in the underlying network topology. A set of studies shows that these approaches can lead to a win-win situation under certain conditions, and to a win-no lose situation in most cases. However, the scenarios used mostly assume homogeneous peer distributions. This is not the case in practice according to recent measurement studies. Therefore, we extend previous work in this paper by studying scenarios with real-life, skewed peer distributions. We show that even a win-no lose situation is difficult to achieve under those conditions and that the actual impact for a specific peer heavily depends on the used locality-aware peer selection and the specific scenario. This contradicts the principle of economic traffic management (ETM), which aims for a solution where all involved players benefit and consequently have an incentive to adopt locality awareness. Therefore, we propose and evaluate refinements of current proposals, allowing all users of P2P networks to be sure that their application performance is not reduced. This mitigates the unfairness introduced by current proposals which is a key requirement for a broad acceptance of the concept of locality awareness in the user community of P2P networks.

Poster: P2P search routing concepts for mobile object tracking

Mobile object tracking is the process of tracking objects which are moving constantly in their environment and thus change their location and context. We present in this paper a decentralized data management solution based on peer-to-peer (P2P) concepts and in particular a distributed hash table (DHT). Sensor network nodes run a DHT system, to which tracked objects or sensors insert their data about the objects. This distributed data storage can be queried by the application according to the DHT principles in order to retrieve the current status of an object without stability or bottleneck problems. Moreover, for scalability, our concept comprises a two tier architecture where we separate local tracking systems, which deal with frequent updates in a constrained local environment, and global tracking. In this way a second tier DHT based P2P system interconnects all local P2P systems for a global query resolution.

An Operator Approach to Popularity-Based Caching in DHTs

Caching is a long investigated topic in the context of P2P networks and distributed hash tables (DHTs). Most of the proposed caching algorithms are user-centric in the sense that they focus on minimizing the search size or latency as the target metrics. In contrast, we take the network operator-centric view in this paper. We set the total traffic generated by the DHT search as the metric of interest and provide a simple algorithm to achieve a maximum reduction of the traffic. The key of the algorithm is that every node maintains statistics about routed queries and replicates its cached objects only when the popularity of queries for those objects are above a certain threshold. Through extensive simulations, we determine the optimal value of the popularity threshold and show the traffic reduction in comparison with state of the art DHT caching solutions. Our algorithm achieves an average traffic reduction of around 30% as compared to caching along the entire search paths, while maintaining good performance in terms of user-oriented measures such as the number of search hops, or equivalently, the search latency.

P-Gate: Pushing the operator service platform towards the network edge

In order to extend the coverage of network-based services to the home environment and offload core network servers, this paper presents a novel service platform called P-Gate that resides in home gateways such as femtocells or wireless LAN access points. The P-Gate platform allows for scalability through self-organized overlay techniques and supports a full integration with centralized service nodes such as the IP Multimedia Subsystem (IMS) to provide functionality like authorization, accounting and bootstrapping. The overlay system scalability has been shown through large-scale simulations and in a Planet—Lab deployment. Further, we have implemented the P-Gate platform on the basis of wireless LAN access points. It serves as a testbed for IMS evolution concepts towards a next generation service platform based on distributed service nodes.