BitTorrent was conceived as a way of distributing large files more quickly, efficiently, and reliably. Thanks to BitTorrent though, the download of large files has become more feasible, and people have become accustomed to acquiring video through the net. At this point it is virtually impossible for anyone to bring an end to illegal downloads. whether or not BitTorrent will continue to play a role in this is yet to be seen

1. Submitted To:-
Mr. Nayyar Khan
Miss Suhani Agarwal
Submitted By:-
Ankit Malvi CSE-16
Ankit Chauhan CSE-14
Himanil Gupta CSE-39

2. Contents…
 Simple Solution: One BIG Server (but a problem too…)
 How server Works…?
 Solution Of the problem
 Entering “BIT TORRENT”..
-Something about creator……
-Definition
-Basic Component
-Basic Idea

3. Simple Solution: One Big Server
 Make the file available on a central server
 Each client downloads file from this server
 Problems
 Solution does not scale very well
 With a large number of clients, the server’s resources get
overwhelmed

5. How SERVER works?

6. Problem Being Solved Here?
 Sharing a fairly large file
 Involves making a replica
 Problem is somewhat similar to, but not the same as,
replication in a distributed file system, a Content
Delivery Network or a Distributed Hash Table overlay
network

7. Entering Bit Torrent
 Released in the summer of 2001
 Uses basic ideas from game theory to largely eliminate
the free-rider problem
 All previous systems could not deal with this problem
well
 Makes no strong guarantees unlike DHTs
 It is working extremely well in practice, unlike DHTs 

8. Something About Creator…..
Bram Cohen – the creator of Bit Torrent:

9. What is BitTorrent?
Efficient content distribution system using
file swarming. Usually does not perform
all the functions of a typical p2p system,
like searching.

10. Basic Components
 Seed
 Peer that has the entire file
 Leeches
 Peer that has an incomplete copy of the file
 A Torrent file
 Passive component
 Files are typically fragmented into 256KB pieces
 The torrent file lists SHA1 hashes of all the pieces to allow peers to
verify integrity
 Typically hosted on a web server
 A Tracker
 Active component
 Allows peers to find each other
 Returns a random list of peers

11. Basic Idea
 Initial seeder chops file into many pieces.
 Leecher first locates the .torrent file that directs it to a
tracker, which tells which other peers are downloading
that file. As a leecher downloads pieces of the file, replicas
of the pieces are created. More downloads mean more
replicas available
 As soon as a leecher has a complete piece, it can potentially
share it with other downloaders. Eventually each leecher
becomes a seeder by obtaining all the pieces, and
assembles the file. Verifies the checksum.

12. BitTorrent Lingo
Seeder = a peer that provides the complete file.
Initial seeder = a peer that provides the initial copy.
Leecher
Initial seeder One who is downloading
(not a derogatory term)
Leecher
Seeder

13. Pieces & Sub-Pieces
 A piece is broken into sub-pieces ... typically 16KB in
size
 Policy: Until a piece is assembled, only download sub-
pieces for that piece
 This policy lets complete pieces assemble quickly

14. File sharing
Large files are broken into pieces of size between
64 KB and 1 MB
1 2 3 4 5 6 7 8

15. Simple example
{1,2,3,4,5,6,7,8,9,10}
Seeder: A
{1,2,3}
{1,2,3,4,5}
Downloader C
Downloader B

17. How delay is avoided between pieces..??
 When transferring data over TCP, it is critical to
always have several requests pending at once, to
avoid a delay between pieces being sent
 Bit Torrent breaks pieces into sub-pieces
 At any point in time, some number, typically 5, are
requested simultaneously
 Every time a sub-piece arrives, a new request is
sent
 This scheme has been found to saturate most
connections in practice

18. BT: internal mechanism
 Built-in incentive mechanism (where all the
magic happens):
 Choking Algorithm
 Optimistic Unchoking

19. Choking
 Choking is a temporary refusal to upload. It is one
of BitTorrent’s most powerful idea to deal with free
riders (those who only download but never
upload).
 Tit-for-tat strategy is based on game-theoretic
concepts.

20. Choking Algorithm
 Goal is to have several bidirectional connections
running continuously
 Upload to peers who have uploaded to you recently
 Unutilized connections are uploaded to on a trial basis
to see if better transfer rates could be found using
them

21. Choking Specifics number of its peers
 A peer always unchokes a fixed
(default of 4)
 Decision to choke/unchoke done based on current
download rates, which is evaluated on a rolling 20-
second average
 Evaluation on who to choke/unchoke is performed
every 10 seconds
 This prevents wastage of resources by rapidly choking/unchoking
peers
 Supposedly enough for TCP to ramp up transfers to their full
capacity
 Which peer is the optimistic unchoke is rotated
every 30 seconds

22. Optimistic unchoking
 A BitTorrent peer has a single “optimistic
unchoke” to which it uploads regardless of the
current download rate from it. This peer rotates
every 30s
 Reasons:
 To discover currently unused connections are
better than the ones being used
 To provide minimal service to new peers

23. Endgame Mode
 Policy: When all the sub-pieces that a peer doesn’t
have are actively being requested, these are
requested from EVERY peer
 When the sub-piece arrives, the replicated
requests are cancelled
 This ensures that a download doesn’t get prevented
from completion due to a single peer with a slow
transfer rate
 Some bandwidth is wasted, but in practice, this is
not too much

25. Bit Torrent p2p file-sharing
system
Aspects important for the
acceptance of a p2p
system :
1. High availability;
2. Users always receive a
good version of the
content they are
requesting;
3. Ability to deal with
flashcrowds;
4. High download speed.

26. Upload-Only mode
 Once download is complete, a peer has no
download rates to use for comparison nor has any
need to use them
 The question is, which nodes to upload to?
 Policy: Upload to those with the best upload rate.
 This ensures that pieces get replicated faster
 Also, peers that have good upload rates are
probably not being served by others

27. conclusion

28. Open any torrent client say BitTorrent ,BitLord..

36. That’s all …..
You are done……
You got your torrent file……….

37. Next What ???
 Now you need to share it! You can upload it to a forum,
or a BitTorrent site, like www.MiniNova.com etc……
 Make sure your client is ready to seed to those who
want the file before you upload, though, or else no one
will get it.

38. Conclusion
 BitTorrent was conceived as a way of distributing
large files more quickly, efficiently, and reliably.
Thanks to BitTorrent though, the download of
large files has become more feasible, and people
have become accustomed to acquiring video
through the net. At this point it is virtually
impossible for anyone to bring an end to illegal
downloads. whether or not BitTorrent will
continue to play a role in this is yet to be seen.

39. References
 Google Search…
 www.en.wikipedia.com.com
 www.howstuffsworks.com
 www.what-is-torrent.com
 Torrent s/w official websites

40. Thank You…..
Questions…??