BitTorrent

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1. BitTorrent is created by Bram Cohen in 2001.
2. It is peer to peer (P2P) file sharing communication protocol.It is a peer to peer in nature ,users connected to each other directly to send and receive the portions of the file.
It used to transfer very huge files.
The key philosophy of Bit Torrent is that user should upload at the same time they downloading.
5. BitTorrent provides protocol to all torrent clients.
6. This is most popular and efficient file transferring system.
7. More efficient than client – server system.
Client – server working
Client send the request to server
Server send files
Transfer is handled by FTP and HTTP.
Client Responsibility
Handle the user interface.
Translate the user's request into the desired protocol.
Send the request to the server.
Wait for the server's response.
Translate the response into "human-readable" format.
Present the results to the user.
Server Responsibilty
Wait for a client's request.
Process that request.
Return the results back to the client.
Client-Server Disadvantages
When the number of client request to server increases,server become overloaded.
Crashes whole system when Server crashes.
Peer to peer Architecture
File to be transfer is divided into equal size of pieces.
These pieces are downloaded from different peers parallely.
components
BitTorrent Client Software
.torrent file or METAinfo file
Leechers
Peers
Seeds
Tracker
Piece (of a file)
Data
Torrent index server
Torrent File / Metafile
It has extension as .torrent
It is extremely small ( up to 100KB )
It is downloaded from torrent index server
contains the information that points to the actual file and the people who are sharing it.
Contents of .torrent file –
Info
size of piece
total no. piece
SHA number
announce
creation date
comment
created by
seeds
These are the clients who has entire file
They uploads files to other peers
This is the peer which does not have entire file
They uploads part of file at same time when they downloads other part.
peers
It is the client which is responsible for file transfer
Downloading speed of any file using torrent depends on number of peers.
Peers = leech + seed
Piece(of a file)
The file which to be download is divided similar size of pieces.
These pieces are downloaded parallel
Each pieces is download from different peers
Tracker
Tracker is the server
It contains all database about peers of a torrent
It provides all list of peers which are associated with a particular torrent
These trackers are mentioned in the Metafile
Client S/W sends request to send list of peers
connects to all peers
Torrent index website
Source of .torrent files
Torrent search engine
advantages
BitTorrent is an open-source program offers a spyware- and nuisance-free installation. 
Allows users to share large amounts of data in a short span of time.
Discourages “freeloading” by rewarding fastest uploaders.
The more popular a file is — the more people want a copy of it — the faster it can be downloaded, because there are more places to get pieces of it.