Optimizing and Balancing Load in Fully Distributed P2P File Sharing Systems

International audienceA peer-to-peer file sharing system includes a lookup and a content distribution protocol. Very efficient peer-to-peer protocols exist for content distribution, but efficient indexing is still an open problem. Numerous work on structured overlay networks such as distributed hash tables offer a promising framework. However, balancing the load of publishing, storing indexes and answering request still remains a challenging task. We sketch a general architecture frame-work for solving these problems in the case of a file sharing application. Our design goals include reducing the work of file providers (they should not bare all the publishing process) and enabling keyword searching based on the assumption that few words are associated with each file

Broose : A Loose Distributed HashtableBased on the De-Brujin Topology

We describe a peer-to-peer system similar to Ka­demlia based on the De-Brujin topology with provable consistency and allowing every message exchange to reinforce contact information. Ultimately simple routing tables are achieved by maintaining only two «buckets» of neighbors and providing maximal accuracy of routing tables

Broose: A Practical Distributed Hashtable Based on the De-Brujin Topology

Broose is a peer-to-peer protocol based on the De-Brujin topology allowing a distributed hashtable to be maintained in a loose manner. Each association is stored on k nodes to allow higher reliability with regard to node failures. Redundancy is also used when storing contacts avoiding complex topology maintenance for node departures and arrivals. It uses a constant size routing table of O(k) contacts for allowing lookups in O(log N) message exchange (where N is the number of nodes participating). It can also be parametrized for obtaining O(log N / log log N) steps lookups with a routing table of size O(k log N). These bounds hold with high probability. Moreover, the protocol allows load balancing of hotspots of requests for a given key as well as hotspots of key collisions. The goal is to obtain a protocol as practical as Kademlia based on the De-Brujin topology

Broose: A Practical Distributed Hashtable Based on the De-Bruijn Topology

International audienceBroose is a peer-to-peer protocol based on the De-Brujin topology allowing a distributed hashtable to be maintained in a loose manner. Each association is stored on k nodes to allow higher reliability with regard to node failures. Redundancy is also used when storing contacts avoiding complex topology maintenance for node departures and arrivals. It uses a constant size routing table of O(k) contacts for allowing lookups in O(log N) message exchange (where N is the number of nodes participating). It can also be parametrized for obtaining O(log N / log log N) steps lookups with a routing table of size O(k log N). These bounds hold with high probability. Moreover, the protocol allows load balancing of hotspots of requests for a given key as well as hotspots of key collisions. The goal is to obtain a protocol as practical as Kademlia based on the De-Brujin topology

PrefixStream: A Balanced, Resilient and Incentive Peer-to-Peer Multicast Algorithm

We consider the problem of multicasting a stream of packets in a large scale peer-to-peer environment. In that context, we stress three features: forwarding load should be equally balanced among nodes, the scheme should be resilient to node failures and peers should have incentive to cooperate. Mainly based on the seminal work of SplitStream which partially achieves this goals, we propose an algorithm gathering together these three features. Its main advantage is to reduce the forwarding load of every node to the stream bandwidth (every node uploads as much as it downloads). This ultimate load balancing is achieved together with a clustering scheme allowing bi-directional exchanges. This results in resilience to node failures and the possibility of banishing nodes that do not respect reciprocity of exchanges. This paper promotes disjoint clustering as opposed to previously proposed hierarchical clustering schemes. Interestingly, varying the size of clusters allows to obtain different trade-offs between delay optimization and resilience to node failures. The performances of several algorithms are analyzed and compared with respect to these goals. The propagation delays of these algorithms appear to be within a factor 1.5 to 2 from theoretical optimal

Stratification in P2P Networks - Application to BitTorrent

We introduce a model for decentralized networks with collaborating peers. The model is based on the stable matching theory which is applied to systems with a global ranking utility function. We consider the dynamics of peers searching for efficient collaborators and we prove that a unique stable solution exists. We prove that the system converges towards the stable solution and analyze its speed of convergence. We also study the stratification properties of the model, both when all collaborations are possible and for random possible collaborations. We present the corresponding fluid limit on the choice of collaborators in the random case. As a practical example, we study the BitTorrent Tit-for-Tat policy. For this system, our model provides an interesting insight on peer download rates and a possible way to optimize peer strategy

Acyclic Preference Systems in P2P Networks

In this work we study preference systems natural for the Peer-to-Peer paradigm. Most of them fall in three categories: global, symmetric and complementary. All these systems share an acyclicity property. As a consequence, they admit a stable (or Pareto efficient) configuration, where no participant can collaborate with better partners than their current ones. We analyze the representation of the such preference systems and show that any acyclic system can be represented with a symmetric mark matrix. This gives a method to merge acyclic preference systems and retain the acyclicity. We also consider such properties of the corresponding collaboration graph, as clustering coefficient and diameter. In particular, studying the example of preferences based on real latency measurements, we observe that its stable configuration is a small-world graph

Stratification in P2P Networks - Application to BitTorrent

We introduce a model for decentralized networks with collaborating peers. The model is based on the stable matching theory which is applied to systems with a global ranking utility function. We consider the dynamics of peers searching for efficient collaborators and we prove that a unique stable solution exists. We prove that the system converges towards the stable solution and analyze its speed of convergence. We also study the stratification properties of the model, both when all collaborations are possible and for random possible collaborations. We present the corresponding fluid limit on the choice of collaborators in the random case. As a practical example, we study the BitTorrent Tit-for-Tat policy. For this system, our model provides an interesting insight on peer download rates and a possible way to optimize peer strategy

On Using Matching Theory to Understand P2P Network Design

This paper aims to provide insight into stability of collaboration choices in P2P networks. We study networks where exchanges between nodes are driven by the desire to receive the best service available. This is the case for most existing P2P networks. We explore an evolution model derived from stable roommates theory that accounts for heterogeneity between nodes. We show that most P2P applications can be modeled using stable matching theory. This is the case whenever preference lists can be deduced from the exchange policy. In many cases, the preferences lists are characterized by an interesting acyclic property. We show that P2P networks with acyclic preferences possess a unique stable state with good convergence properties

Incentive, Resilience and Load Balancing in Multicasting through Clustered de Bruijn Overlay Network

In this paper, we consider the problem of multicasting a stream of packets in a large scale peer-to-peer environment. In that context peers should have incentive to cooperate. We present PrefixStream, an algorithm that addresses this problem by using reciprocity in packet forwarding. Each node thus has incentive to forward since recipients send back other packets of the stream. To achieve this efficiently, PrefixStream strips the content across two sets of clustered trees built upon the symmetric de Bruijn graph. This both allows to banish nodes that do not respect reciprocity of exchanges and gives resilience to node failures. Furthermore, it reduces the forwarding load of every node to the stream bandwidth (every node uploads as much as it downloads) even when the size of its cluster varies. Conversely to previously proposed hierarchical schemes, PrefixStream promotes disjoint clustering. This enables loose maintenance and network latencies optimization. We sketch the design of PrefixStream and analyze its performances