Dasher: A peer-to-peer content distribution system based on combined network coding

Network coding can ease the block scheduling and thus makes the distribution more efficient. However, the complexities of encoding and decoding increase sharply as the content size scales up. In this paper, we propose a coding scheme which combines chunked coding and sparse linear network coding to reduce both encoding and decoding costs of content distribution. Based on the combined scheme, we implement a P2P content distribution system, named Dasher, where Local-Rarest-First scheme is adopted for chunk scheduling. Under the same system architecture, we implement three comparative systems, a BitTorrent-like system, named Mybt, a system only with sparse coding, named Sparser and a system using chunked coding, named Chunker. We conduct extensive experiments to compare the performance among these four systems. The experimental results show that Dasher with certain chunk sizes can reduce the average downloading time up to 15% compared with Mybt, and up to 43% with Chunker. With proper chunk sizes, the downloading time of Dasher is almost the same with Sparser. The average decoding rate of Dasher is the same with Chunker, and is nearly m times as fast as Sparser, where m is the number of chunks. Moreover, with respect to robustness, Dasher performs almost as well as Chunker, better than Mybt, but worse than Sparser.