THE BITTORRENT

1
THE BITTORRENT

• P2P FILE-SHARING
• System

2
Overview

• Definition
• Terminology
• Requirements
• File Transfer Process
• Advantages
• References

3
Definition

• Network Application Protocol
• Fragmented File Transfer Process
• Breaks files into fixed length fragments
• Checksum/Hash value is assigned to each fragment
• Torrent/Metadata file
• File Directory Location URL
• File Information name, fragment lengths,
  checksum/hash code, etc.
• Decentralized Directory
• Multiple locations for file content directories
• Multiple TCP (Transport Control Protocol) ports
• Determines download speed
• tit-for tat system

4
Terminology

• Torrent metadata file describing the file(s) to
  be shared.
• Peer user that is acquiring a file
• Seed A peer that has the complete file and is
  actively sharing it.
• Reseed reintroducing a file to the network
• Leech A person that is in the process of
  acquiring a file
• Swarm ad-hoc network formed by users
• Tracker manages bittorrent protocol

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BitTorrent Example Scenario

• swarm

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Requirements Add Port

• A internet connection with port 6881,68826889
• Update Network and Internet Connections settings
  to add BitTorrent information
• Description BitTorrent
• Name or IP address 127.0.0.01 ( local machine)
• External port and Internal port 6881

7
Requirements Tracker
8
Requirements Client

• BitTorrent client software
• Handles BitTorrent File Transfer Interactions
• BitComet for windows, http//www.bitcomet.com/

9
Requirements Client continued
10
Requirements Client Continuted

• Bitcomet provides the option to make a .torrent
  file
• Common inclusions
• Names of the files
• Sizes
• Checksum/hash code of all blocks (added by
  software)
• Address of the tracker

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Requirements Search Engine

• Many BitTorrent websites act as both tracker and
  index.
• Publicize the tracker's URL
• Allow users to upload torrents to the index with
  the tracker's URL embedded in them, providing all
  the features necessary to coordinate a download.
• BitTorrent Tracker (hosted on the web server)
• Does not necessarily list files that are being
  tracked
• Assists in the communication between peers
• Responds to Client by providing peer id, IP and
  port numbers Peer selection algorithms
• Connects to port 6969
• Free download available on client site
• BitTorrent Index
• A list of .torrent files (usually including
  descriptions and other information

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File Sharing Process

• Activate Tracker
• Manages and monitors Peer to Peer Communication
• Provides Status of Requests
• Open Client
• User locates desired file (Link to Torrent Sites
  Provided by client)
• Selects download Link
• Tracker receives a HTTP GET request (CGI method)
  from client
• Dependant on the client, a peer can also be a
  tracker (tracker-less)
• Responds with peers information - identifies
  Swarm with desired file fragments
• Client establishes peer communication AKA
  Handshaking with Tracker assistance
• Locate and open available port (starts with 6881
  and work upward to 6889)
• Send Character 19 (base 10) followed by the
  string BitTorrent Protocol
• Send a 20 byte SHA1 hash code from the metafile
• If it does not match between peers the connection
  is closed
• Send a 20 byte peer id
• Used in tracker requests and included in peer
  requests
• Connection is closed if peer id does not match
  the one provided by tracker
• Client handles download process
• Requests Random First Piece

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File Sharing Process continued

• Endgame Mode
• Download delays are avoided by requesting final
  fragment, needed to complete download, from
  entire swarm versus one peer who may have slow
  transfer rates.
• Client handles upload process
• Optimize bandwidth usage
• Choking (temporary refusal to upload torrents)
• Uploading client is already uploading at full
  capacity
• Seed is uninterested in receiving fragments
• Optimistic Unchoking
• Unchoke peers that makes it possible to increase
  bandwidth to an optimal level - Starts uploading
  to peers that have better upload rates in the
  network
• Avoid bandwidth waste
• Fixed intervals for Choking and unchoking
  decisions
• Discontinue upload to choked peers aka
  Anti-Snubbing

14
Questions?
15
References

• Research
• www.slyck.com
• www.peertopeercentral.com
• http//en.wikipedia.org/wiki/bittorrent
• www.bitcomet.com
• http//morehawes.co.uk/
• Free BitTorrent Applications (use decentralized
  P2P)
• www.bitcomet.com
• For windows OS
• http//utorrent.com/
• For LINUX and MAC OS