Design and Implementation of a Collaborative Content Downloading System

Though BitTorrent is an extremely popular and cost efficient P2P file distribution system, it is not able to efficiently utilize all available bandwidth. BitTorrent employs fairness and anti-freeriding mechanisms that function optimally in scenarios when broadband connections are symmetric. However, the majority of peers in BitTorrent swarms have asymmetric broadband connections. This makes it virtually impossible for BitTorrent clients to gain maximum utilization of the downstream capacity. In this thesis, we present Collaborative BitTorrent (CBT), an extension to the BitTorrent protocol that allows groups of users – friends who are willing to share their bandwidth with each other – to team up and engage in a coordinated distributed job to speed up the process of downloading a piece of content. Complementary resources provided by friends enable CBT to achieve a significant improvement in the download performance. We present experimental results that confirm that CBT outperforms the original BitTorrent and is able to fully utilize the available download capacity in most cases.