CS 259 Final Project Report: BitTorrent

In BitTorrent, the data to be shared is divided into many equal-sized portions called pieces. Each piece is further sub-divided into equal-sized sub-pieces called blocks. All clients interested in sharing this data are grouped into a swarm, each of which is managed by a central entity called the tracker. Each client independently finds a file, called a torrent, that contains the location of the tracker along with a hash of each piece. Clients keep each other updated on the status of their download. Clients download blocks from other (randomly chosen) clients who claim they have the corresponding data. Accordingly, clients also send data that they have previously downloaded to other clients. Once a client receives all the blocks for a given piece, he can verify the hash of that piece against the provided hash in the torrent. Thus once a client has downloaded and verified all pieces, he can be confident that he has the complete data.