Adapting BitTorrent for Wireless Ad Hoc networks

Mohamed Karim Sbai 1, * Chadi Barakat 1 Jaeyoung Choi 1 Anwar Al Hamra 1 Thierry Turletti 1
* Corresponding author
1 PLANETE - Protocols and applications for the Internet
Inria Grenoble - Rhône-Alpes, CRISAM - Inria Sophia Antipolis - Méditerranée
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 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.
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Submitted on : Monday, April 14, 2008 - 6:56:46 PM
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Mohamed Karim Sbai, Chadi Barakat, Jaeyoung Choi, Anwar Al Hamra, Thierry Turletti. Adapting BitTorrent for Wireless Ad Hoc networks. AdHoc-Now Networks and Wireless conference, Sep 2008, Sophia Antipolis, France. ⟨inria-00196313v2⟩

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