Despite its popularity, relatively little is known about the traffic characteristics of the Skype VoIP system and how they differ from other P2P systems. We describe an experimental study of Skype VoIP traffic conducted over a five month period, where over 82 million datapoints were collected regarding the population of online clients, the number of supernodes, and their traffic characteristics. This data was collected from September 1, 2005 to January 14, 2006. Experiments on this data were done in a black-box manner, i.e., without knowing the internals or specifics of the Skype system or messages, as Skype encrypts all user traffic and signaling traffic payloads. The results indicate that although the structure of the Skype system appears to be similar to other P2P systems, particularly KaZaA, there are several significant differences in traffic. The number of active clients shows diurnal and work-week behavior, correlating with normal working hours regardless of geography. The population of supernodes in the system tends to be relatively stable; thus node churn, a significant concern in other systems, seems less problematic in Skype. The typical bandwidth load on a supernode is relatively low, even if the supernode is relaying VoIP traffic.

The performance of peer-to-peer file replication comes from its piece and peer selection strategies. Two such strategies have been introduced by the BitTorrent protocol: the rarest first and choke algorithms. Whereas it is commonly admitted that BitTorrent performs well, recent studies have proposed the replacement of the rarest first and choke algorithms in order to improve efficiency and fairness. In this paper, we use results from real experiments to advocate that the replacement of the rarest first and choke algorithms cannot be justified in the context of peer-to-peer file replication in the Internet. We instrumented a BitTorrent client and ran experiments on real torrents with different characteristics. Our experimental evaluation is peer oriented, instead of tracker oriented, which allows us to get detailed information on all exchanged messages and protocol events. We go beyond the mere observation of the good efficiency of both algorithms. We show that the rarest first algorithm guarantees close to ideal diversity of the pieces among peers. In particular, on our experiments, replacing the rarest first algorithm with source or network coding solutions cannot be justified. We also show that the choke algorithm in its latest version fosters reciprocation and is robust to free riders. In particular, the choke algorithm is fair and its replacement with a bit level tit-for-tat solution is not appropriate. Finally, we identify new areas of improvements for efficient peer-to-peer file replication protocols.

... to flood Internet access and backbone ISPs with massive amounts of new traffic. We recently measured 200,000 IPTV users for a single program, receiving at an aggregate simultaneous rate of 100 gigabits/second. Although many architectures are possible for IPTV video distribution, several chunkdriven P2P architectures have been successfully deployed in the Internet. In order to gain insight into chunk-driven P2P IPTV systems and the traffic loads they place on ISPs, we have undertaken an in-depth measurement study of one of the most popular IPTV systems, namely, PPLive. We have developed a dedicated PPLive crawler, which enables us to study the global characteristics of the chunk-driven PPLive system. We have also collected extensive packet traces for various different measurement scenarios, including both campus access network and residential access networks. The measurement results obtained through these platforms bring important insights into IPTV user behavior, P2P IPTV traffic overhead and redundancy, peer partnership characteristics, P2P IPTV viewing quality, and P2P IPTV design principles.

Recently, peer-to-peer (P2P) networks have emerged as an attractive solution to enable large-scale content distribution without requiring major infrastructure investments. While such P2P solutions appear highly beneficial for content providers and end-users, there seems to be a growing concern among Internet Service Providers (ISPs) that now need to support the distribution cost. In this work, we explore the potential impact of future P2P file delivery mechanisms as seen from three different perspectives: i) the content provider, ii) the ISPs, and iii) individual content consumers. Using a diverse set of measurements including BitTorrent tracker logs and payload packet traces collected at the edge of a 20,000 user access network, we quantify the impact of peer-assisted file delivery on end-user experience and resource consumption. We further compare it with the performance expected from traditional distribution mechanisms based on large server farms and Content Distribution Networks (CDNs).

Abstract — BitTorrent (BT) in the last years has been one of the most effective mechanisms for P2P content distribution. Although BT was created for distribution of time insensitive content, in this work we try to identify what are the minimal changes needed in the BT’s mechanisms in order to support streaming. The importance of this capability is that the peer will now have the ability to start enjoying the video before the complete download of the video file. This ability is particularly important in highly polluted environments, since the peer can evaluate the quality of the video content early and thus preserve its valuable resources. In a nutshell, our approach gives higher download priority to pieces that are close to be reproduced by the player. This comes in contrast to the original BT protocol, where pieces are downloaded in an out-of-order manner based solely on their rareness. In particular, our approach tries to strike the balance between downloading pieces in: (a) playing order, enabling smooth playback, and (b) the rarest first order, enabling the use of parallel downloading of pieces. In this work, we introduce three different Piece Selection mechanisms and we evaluate them through simulations based on how well they deliver streaming services to the peers. I.

Existing studies on BitTorrent systems are single-torrent based, while more than 85 % of all peers participate in multiple torrents according to our trace analysis. In addition, these studies are not sufficiently insightful and accurate even for single-torrent models, due to some unrealistic assumptions. Our analysis of representative Bit-Torrent traffic provides several new findings regarding the limitations of BitTorrent systems: (1) Due to the exponentially decreasing peer arrival rate in reality, service availability in such systems becomes poor quickly, after which it is difficult for the file to be located and downloaded. (2) Client performance in the BitTorrentlike systems is unstable, and fluctuates widely with the peer population. (3) Existing systems could provide unfair services to peers, where peers with high downloading speed tend to download more and upload less. In this paper, we study these limitations on torrent evolution in realistic environments. Motivated by the analysis and modeling results, we further build a graph based multi-torrent model to study inter-torrent collaboration. Our model quantitatively provides strong motivation for inter-torrent collaboration instead of directly stimulating seeds to stay longer. We also discuss a system design to show the feasibility of multi-torrent collaboration. 1

This paper assesses BitTorrent's robustness against selfish peers, who try to download more than their fair share by abusing existing protocol mechanisms. We design and implement three selfish-peer exploits and evaluate their effectiveness on public and private torrents. In practice, BitTorrent appears quite robust against this kind of exploit: selfish peers can sometimes obtain more bandwidth, and honest peers' download rates suffer slightly in consequence, but we observe no considerable degradation of the system's quality of service. We identify private-torrent scenarios in which a selfish peer could benefit more significantly at the expense of honest peers, and discuss the BitTorrent protocol mechanisms that lead to robustness by rendering these scenarios infeasible.

Most current P2P file-sharing systems treat their users as anonymous, unrelated entities, and completely disregard any social relationships between them. However, social phenomena such as friendship and the existence of communities of users with similar tastes or interests may well be exploited in such systems in order to increase their usability and performance. In this paper we present a novel social-based P2P filesharing paradigm that exploits social phenomena by maintaining social networks and using these in content discovery, content recommendation, and downloading. Based on this paradigm’s main concepts such as taste buddies and friends, we have designed and implemented the TRIBLER P2P file-sharing system as a set of extensions to Bittorrent. We present and discuss the design of TRIBLER, and we show evidence that TRIBLER enables fast content discovery and recommendation at a low additional overhead, and a significant improvement in download performance. 1.

During recent years, Distributed Hash Tables (DHTs) have been extensively studied through simulation and analysis. However, due to their limited deployment, it has not been possible to observe the behavior of a widely-deployed DHT in practice. Recently, the popular eMule file-sharing software incorporated a Kademlia-based DHT, called Kad, which currently has around one million simultaneous users. In this paper, we empirically study the performance of the key DHT operation, lookup, over Kad. First, we analytically derive the benefits of different ways to increase the richness of routing tables in Kademlia-based DHTs. Second, we empirically characterize two aspects of the accuracy of routing tables in Kad, namely completeness and freshness, and characterize their impact on Kad’s lookup performance. Finally, we investigate how the efficiency and consistency of lookup in Kad can be improved by performing parallel lookup and maintaining multiple replicas, respectively. Our results pinpoint the best operating point for the degree of lookup parallelism and the degree of replication for Kad.

Peer-to-peer protocols play an increasingly instrumental role in Internet content distribution. Consequently, it is important to gain a full understanding of how these protocols behave in practice and how their parameters impact overall performance. We present the first experimental investigation of the peer selection strategy of the popular BitTorrent protocol in an instrumented private torrent. By observing the decisions of more than 40 nodes, we validate three BitTorrent properties that, though widely believed to hold, have not been demonstrated experimentally. These include the clustering of similar-bandwidth peers, the effectiveness of BitTorrent’s sharing incentives, and the peers ’ high average upload utilization. In addition, our results show that BitTorrent’s new choking algorithm in seed state provides uniform service to all peers, and that an underprovisioned initial seed leads to the absence of peer clustering and less effective sharing incentives. Based on our observations, we provide guidelines for seed provisioning by content providers, and discuss a tracker protocol extension that addresses an identified limitation of the protocol. 1