Adapting BitTorrent to Wireless Ad Hoc Networks

Abstract

Abstract. BitTorrent 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 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 an enhancement to BitTorrent which aims to minimize the time to download the content and at the same time to enforce cooperation among peers. Our solution considers a restricted neighborhood to reduce routing overhead and to improve throughput, while establishing few connections to remote peers to improve diversity of pieces. 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.

BitHoc: A content sharing application for wireless ad hoc networks

“…Through new peer neighbor selection and content pieces selection strategies, our solution is topology-aware and ensures fair sharing. These strategies have been described in details in our research work [2]. Globally, we found that the best to do is to share the most data with physical neighbors to reduce the network overhead and to realize the maximum throughput, while sending pieces of content from time to time to far peers to provide them with material to share and keep them busy.…”

“…plugged and used into mobile devices [2]. Indeed, on one hand, their algorithms are not adapted to the constraints of multi-hop wireless networks.…”

“…We propose a BitTorrent [1] variant called BitHoc,adapted to the wireless ad hoc network environment, which is the result of our research work [2]. Our architecture consists of two main components: a membership management service (BitHoc Tracker) and a content sharing service (BitHoc client).…”

“…This service adapts the peer neighbor and piece selection strategies of BitTorrent to account for the topology of the network and the scarcity and shared nature of resources. The algorithms of BitHoc are described in [2]. We developed our software on mobile devices having Windows Mobile 6 as an operating system and equipped with WIFI adapters.…”

Revisiting P2P Content Sharing in Wireless Ad Hoc Networks

“…This is contradictory to the goals of BitTorrent and is not suitable for wireless ad hoc networks. In another previous work [3], we propose replicating the initial seed of the content at the edge of the network in order to increase the diversity and improve the parallelism. Although these policies recofd better download times and point to some new directions, they are limited to some specific cases that need to be generalized to clearly illustrate the relationship between content replication, user performance, fairness and overhead on the underlying network.…”