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Bit Torrent Protocol
1.
2. CONTENTS
INTRODUCTION
OTHER FILE TRANSFOR METHODS
STRIKING CHARACTERISTICS
TERMINOLOGY
ARCHITECTURE OF BITORRENT
COMPONENTS OF BITTORRENT SYSTEM
WORKING OF BITTORRENT
CONCLUSION
3. Bit torrent is created by bram cohen
Transfer of large files using the minimum
internet bandwidth
Peer-to-peer file transfer protocol
Files are shared by many users
Active participation of all users
Huge success in the file sharing domain
35% of internet traffic
Introduction
4. Other File Transfer Methods
Typical HTTP file transfer
Download Accelerator Plus (DAP)
Other Peer to Peer systems
• Kazaa, eDonkey, Direct Connect ….
5. Striking Characteristics
A central server is not needed
No single point of failure
More the number of users, greater will be the
transfer rate
Data available in pieces, not as a single large
file
8. HTTP Peer – Tracker
TCP Peer – Peer
Components of BitTorrent System
Metainfo File
Data
Tracker
Peers
Client
9. Metainfo file
Containes all information about a
torrent
File with a .torrent extension
Encoding scheme used by bittorrent is
called bencoding
Hash of all the pieces are present in
info field of metainfo file
10. Data
Data can be a single file or multiple files
contained in a directory
Data is split into many pieces of equal size
Each piece is further divided into many
blocks
A piece will have a hash, needed for data
integrity check
Common piece sizes are 256kb, 512kb and
1mb
11. Tracker
Manages users participating in a torrent
Helps peers find each other
It is a HTTP service that works on port 6969
Peers request tracker for other peers having
the required pieces
Tracker responds with a list of peers that
have the requested piece
A tracker can manage many torrents
12.
13. Scraping
Querying the state of a given torrent
Tracker responds with a scrape page
Announce URL : http://example.com/announce
Scrape URL : http://example.com/scrape
Scrape page has the following keys
• complete
• incomplete
• downloaded
14. Peers
Ports 6881 – 6889 are used by peers
Peers speak TCP
Following are the key strategies used by
peers while sharing files
• Random First Piece
• Rarest First
• Endgame Mode
• Peer Distribution
• Choking
• Optimistic Unchoking
15. Peers perform a handshake to start the
communication
Handshaking involves these messages
• Character 19 followed by ‘BitTorrent Protocol’
• 20 bytes hash of the info field from metainfo file
• 20 bytes peer id
Peers start talking to each other
They pass a number of messages between
them to send data and control the interactions
16. Client
Executable program running on user’s
machine
Co ordinates with OS to perform read write
operations
A .torrent file must be opened by the client
Peers with same client perform better
17. Working of BitTorrent
1. Seeder generates a
torrent file and
uploads torrent to a
web server.
2. The seeder notifies
the tracker that it is
sharing the file
described in the
torrent file.
18. 3. A leecher
downloads the
torrent file from the
web server.
4. The leecher
connects to the
tracker specified in
the torrent file.
20. Conclusion
BitTorrent is a popular P2P technology deployed
across the Internet.
The protocol has found a niche as a preferred
method for the decentralized distribution of large
files.
It provides data integrity which ensures that the
data will always be genuine and free from flaws.
BitTorrent uses tit for tat exchange to increase
cooperation among peers and has developed a
reputation for being efficient, scalable, and robust.