Angels: In Network Support for Minimum Distribution Time in P2P Overlays
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Citation (published version)Sweha, Raymond; Bestavros, Azer; Byers, John. "Angels -- In-Network Support for Minimum Distribution Time in P2P Overlays", Technical Report BUCS-TR-2009-003, Computer Science Department, Boston University, February 10, 2009. [Available from: http://hdl.handle.net/2144/1726]
This paper proposes the use of in-network caches (which we call Angels) to reduce the Minimum Distribution Time (MDT) of a file from a seeder – a node that possesses the file – to a set of leechers – nodes who are interested in downloading the file. An Angel is not a leecher in the sense that it is not interested in receiving the entire file, but rather it is interested in minimizing the MDT to all leechers, and as such uses its storage and up/down-link capacity to cache and forward parts of the file to other peers. We extend the analytical results by Kumar and Ross  to account for the presence of angels by deriving a new lower bound for the MDT. We show that this newly derived lower bound is tight by proposing a distribution strategy under assumptions of a fluid model. We present a GroupTree heuristic that addresses the impracticalities of the fluid model. We evaluate our designs through simulations that show that our Group-Tree heuristic outperforms other heuristics, that it scales well with the increase of the number of leechers, and that it closely approaches the optimal theoretical bounds.