BitTorrent Protocol
Dosed by Swapna K M – M & E Team (from MphasiS Software Services)
What is a BitTorrent Protocol?
BitTorrent technology has revolutionized how data is shared over the Internet.
It is an open source peer-to-peer file sharing communications protocol used to
share data online between users/peers. The BitTorrent protocol is a cost
effective way to share information across the Internet. One example of
implementation of this technology is how gaming companies use this technology
to upload game updates to all of their consumers. The basic concept of the
BitTorrent protocol is to download various pieces of the desired file from
different peers, as well as simultaneously uploading the downloaded pieces of
the file.
The idea behind BitTorrent is to allow massive distribution of files without
penalizing the source by soaring bandwidth costs and possible crashes due to
demand that exceeds the capability of the server.
Pieces of a same file are downloaded from different peers. However, compared to
other peer-to-peers, BitTorrent does not include a search engine.
There are some terms that need to be understood when talking about BitTorrent
Protocol:
1. Torrent — This is a meta data file that contains what files that are
intended to be downloaded, as well as the trackers IP address.
2. Tracker — Think of tracker as BitTorrent Server. The client contacts the
tracker, and the tracker connects the client to various peers or seeds.
3. Seed — it is a kind of BitTorrent peer. Seeds are peers that have complete
file(s) on their hard drive.
4. Leecher — A kind of BitTorrent peer. Leechers are peers that are downloading
from seeds or a swarm, but are allowing their data to be uploaded.
5. Swarm — A collection of peers that are downloading and uploading at the same
time.
6. Distributed Hash Table (DHT) — Think of DHT technology as a multi-computer
tracker with error checking.
A popular BitTorrent client is uTorrent. uTorrent uses the DHT technology, as
well as allowing the data that is being downloaded and uploaded to be encrypted.
How does it work?
To understand how BitTorrent works, let’s see how a normal downloading works.
Personal computers connected to the Internet are known as clients while the
websites visited reside on Internet servers. Servers "serve up information" to
clients. If you download a file from your computer, you create a one-on-one
connection to that server that uses whatever bandwidth is necessary to serve
you the file. When you have received the entire file, the connection is
released so the server can utilize that stream of bandwidth for handling other
connections.
The problem arises when unusually high numbers of clients visit a site
simultaneously. This can cause the server to effectively run out of available
bandwidth and "crash." When this happens, clients are refused a connection.
To avoid this, BitTorrent creates a different networking scheme. It uses the
other clients who are also downloading the file to effectively act as servers
to one another, simultaneously uploading the parts of the file received to
others requesting the file. Hence, when you click on a file to download,
several connections will be made to receive "slices" of the file that combine
to create the entire file. Meanwhile, as you are downloading these "slices" you
are also uploading them to anyone else that needs the parts you are receiving.
Once the entire file is received it is considered polite to keep your client
connected to act as a seed. A seed refers to a source that has the entire file
available.
To be able to share a file, a small file named “torrent” is first created. The
“torrent” will contain metadata about the files that have to be shared as well
as data about the computer that will coordinate the distribution of the file.
Those who want to download a specific file must hence have the “torrent” file
for it and get connected to the computer responsible for the file distribution.
The computer will hence tell the other users/peers where to get the other
pieces of the file.
Is BitTorrent Legal?
The legality of BitTorrent lies in its contents. There are a number of
sharewares and freeware present that are not subject to any copyright
infringements. However, you should be careful while downloading music and video
files as these are common files that can be distributed illegally. It is quite
simple to guess which type of file is being downloaded with or without the
author’s authorization. You can check on the author’s or program distributor’s
website if it is a commercial or a free file.
Further References
http://en.wikipedia.org/wiki/BitTorrent_(protocol)
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