Submitted To:-

Mr. Nayyar Khan

Miss Suhani Agarwal

Submitted By:-

Ankit Malvi CSE-16

Ankit Chauhan CSE-14

Himanil Gupta CSE-39

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

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

How SERVER works?

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

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

Bram Cohen – the creator of Bit Torrent:

Something About Creator…..

What is BitTorrent?

Efficient content distribution system using

file swarming. Usually does not perform

all the functions of a typical p2p system,

like searching.

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

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.

BitTorrent LingoSeeder = a peer that provides the complete file.

Initial seeder = a peer that provides the initial copy.

Initial seeder

Seeder

Leecher

One who is downloading(not a derogatory term)

Leecher

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

File sharingLarge files are broken into pieces of size between

64 KB and 1 MB

1 2 3 4 5 6 7 8

Simple example

Seeder: A

Downloader B

{1,2,3,4,5,6,7,8,9,10}

Downloader C

{1,2,3}{1,2,3,4,5}

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

BT: internal mechanism

Built-in incentive mechanism (where all the

magic happens):

Choking Algorithm

Optimistic Unchoking

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.

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

Choking Specifics A peer always unchokes a fixed number of its peers

(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

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

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

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.

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

conclusion

Open any torrent client say BitTorrent ,BitLord..

That’s all …..

You are done……

You got your torrent file……….

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.

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.

References Google Search…

www.en.wikipedia.com.com

www.howstuffsworks.com

www.what-is-torrent.com

Torrent s/w official websites

Thank You…..

Questions…??