Experiences on enhancing data collection in large networks

We improve and validate TICP, our TCPfriendly reliable transport protocol to collect information from a large number of Internet entities. A collector machine sends probes to a set of information sources that reply by sending back their reports. TICP adapts the sending rate of probes in a way similar to TCP for the purpose of avoiding network congestion and implosion at the collector. Lost reports are requested again by TICP until they are correctly received by the collector. In a first part of this work, we add to TICP a mechanism to cluster information sources in order to probe sources behind the same bottleneck together. This ensures a smooth variation of network conditions during the collection session and hence, an efficient handling of congestion at network bottlenecks. We run simulations in ns-2 over realistic topologies to compare TICP before and after clustering. We also implement the protocol in C++ and test it over the PlanetLab platform. All experiments prove the outperformance of TICP over non adaptive solutions and the interest of the clustering mechanism in shortening the duration of the collection session and in decreasing the ratio of lost packets. In a second part, we adapt TICP to collect large amounts of information from each data source. By the means of simulations, we compare the performance obtained by TICP to that obtained when the information maintained by the different sources is collected by parallel TCP connections. Again, the simulations show that TICP yields shorter collection sessions due to its inherent multiplexing capability. Finally, in a last part, we study the impact of delegating collection to some proxy sources that collect from other sources on behalf of the collector and that the collector probes later to get their collected data. We explain our method to choose the proxy collectors and we show by simulations that for a judicious choice of proxy collectors, one can decrease considerably the collection session duration

Transport Information Collection Protocol with clustering of information sources

We improve and validate TICP, a TCP-friendly reliable transport protocol to collect information from a large number of sources spread over the Internet . A collector machine sends probes to information sources, which respond by sending back report packets containing their information. TICP adapts the rate of probes in a way to avoid implosion at the collector and congestion in the network. To ensure smooth variation of the congestion control parameters and to probe sources behind the same bottleneck at the same time, we add to TICP a mechanism that clusters information sources. This mechanism is based upon the Global Network Positionning (GNP) Internet coordinate system. By running simulations in ns-2 over realistic network topologies, we prove that TICP with clustering of information sources has shorter collect session duration and causes less packet losses than the initial version that probes sources independently of their location

Revisiting content sharing in wireless ad hoc networks

International audienceClassical content sharing applications like BitTorrent can not be directly used in wireless ad hoc networks. When adapting them to these constrained networks, one faces two main problems. On one hand, exchanging content pieces with far nodes yields an important routing overhead. On the other hand, it is necessary to send some content pieces to far nodes to increase the diversity of information in the network, which fosters reciprocity and parallel exchanges. In this paper, we study both of these problems and propose a joint solution for them. Unlike uni-metric approaches, our solution considers relevant performance metrics together as throughput, sharing and routing overhead. We define a new neighbor selection strategy that balances between sharing and diversification efforts and decides on the optimal scope of a node. It also considers the diversification incentives problem. Through extensive simulations, we prove that our solution realizes both better download time and sharing ratio than uni-metric solutions

A membership management protocol for mobile P2P networks

MANETs are self-organizing networks composed of mobile wireless nodes with often scarce resources. Distributed applications based on the P2P paradigm are the best candidates to run over such networks. To profit from the service provided by a P2P overlay (e.g. file sharing using BitTorrent), a node needs to be permanently informed about the other members of the overlay (e.g. other peers interested in the same file as currently provided by the BitTorrent central tracker). This P2P membership management is a costly and difficult task in such dynamic and resource limited environment. We focus on this problem and we propose a robust, network friendly and decentralized membership management protocol allowing peer discovery and update. Compared to flooding, client-server or multicast based approaches, our protocol achieves significantly lower network overhead and lower pollution of caches caused by peers who have left. Moreover, as network splits are very frequent in MANETs, our protocol is designed to be partition-aware. Namely, it allows separate overlays providing the same service to efficiently merge together when communication opportunities occur. The efficiency of our solution is validated through extensive NS-2 simulations

SPIRA: A Network-Friendly Topology Discovery Protocol

The Internet being very large and rapidly evolving, it is always difficult to maintain a real-time view of its topology without continuously flooding it with a large number of concur- rent probe packets. Although there have been considerable re- search efforts to reduce the number of these probes (e.g. reducing redundancies), the congestion and network overhead they cause have often been overlooked. In this paper, we propose SPIRA, a network-friendly protocol to discover the Internet topology. Our protocol regulates the throughput of probes as a function of the observed delay and loss measurements. Starting from a monitoring computer and a set of destinations, a cartography of intermediate routers (IP addresses and coordinates) and links between them (interfaces and delays) is deduced in a short time and with a minimal overhead. We evaluate the performance of our protocol using real experiments on the PlanetLab testbed

Neighborhood selection in mobile P2P networks

International audienceLa politique de choix des voisins joue un rôle capital dans la détermination de l'efficacité d'une application pair-à-pair pour le partage de fichiers. L'idéal serait d'obtenir des temps de téléchargement minimaux avec le maximum d'opportunittés de partage entre les utilisateurs. Ces applications ont été largement étudiées dans l'Internet, cependant leurs performances dans les réseaux ad hoc mobiles restent à évaluer. En particulier, toute politique de choix des voisins devrait tenir compte de plusieurs contraintes telles que la rareté des ressources radio et leur nature partagée ainsi que la mobilité des noeuds. Dans ce travail, et par l'intermédiaire du fameux protocole BitTorrent, nous étudions l'impact de la mobilité des noeuds sur les performances d'une application de partage de fichiers, et montrons à travers des simulations qu'il est, dans ce cas, inutile de communiquer avec des noeuds lointains car le gain en diversité de piéces de données assuré par cette communication est négligeable devant celui obtenu par la mobilité. En plus, le débit d'envoi de piéces est trés faible sur des chemins longs. Par contre, dans le cas d'un réseau fixe, un envoi sélectif à des noeuds lointains est nécessaire pour l'obtention de bonnes opportunités de partage et une distribution égale des efforts

Adapting BitTorrent for Wireless Ad Hoc networks

International audienceBitTorrent is one of the Internet''s most efficient content distribution protocols. It is known to perform very well over the wired Internet where end-to-end performance is almost guaranteed. However, in wireless ad hoc networks, many constraints appear as the scarcity of resources and their shared nature, which make running BitTorrent in such an environment with its default configuration not lead to best performances. To these constraints it adds the fact that peers are both routers and end-users and that TCP-performance drops seriously with the number of hops. We show in this work that the neighbor selection mechanism in BitTorrent plays an important role in determining the performance of the protocol when deployed over a wireless ad hoc network. It is no longer efficient to choose and treat with peers independently of their location. A first solution is to limit the scope of the neighborhood. In this case, TCP connections are fast but there is no more diversity of pieces in the network: pieces propagate in a unique direction from the seed to distant peers. This prohibits peers from reciprocating data and leads to low sharing ratios and suboptimal utilization of network resources. To recover from these impairments, we propose BitHoc, an enhancement to BitTorrent, which aims to minimize the time to download the content and at the same time to enforce cooperation and fairness among peers. BitHoc considers a restricted neighborhood to reduce routing overhead and to improve throughput, while establishing few connections to remote peers to improve diversity of pieces. To support this, BitHoc modifies the choking algorithm and adds a new piece selection strategy. With the help of extensive NS-2 simulations, we show that these enhancements to BitTorrent significantly improve the file completion time while fully profiting from the incentives implemented in BitTorrent to enforce fair sharing