Peer To Peer (P2P) File Sharing: How It Works
Peter Nisbet
Peer-to-peer (or P2P) file sharing systems connect users
(called nodes) directly together. Some are true networked
systems while other contain an element of the client-server
structure. That is they contain an element of the original
Napster centralized server system where clients are fed by a
central server. Examples of this are the original Napster
(Napster is now a ‘pay for music’ site) and OpenNap which
replicates the original Napster functionality.
It was the central server which eventually destroyed the
Napster system sins, once the server was forced to close, the
whole system ceased to function. The P2P systems are now much
more widely used. In these every user can be connected to every
other user who is logged on. When you download music or movie
files you can be doing so from you next door neighbour, or
someone on the other side of the world. You have access to
literally millions and millions of files: everything on the
other users’ hard disks in fact, and everyone has access to
yours. There is no central server, so the system cannot be shut
down.
Examples are eDonkey, which is combined with Overnet, the
FastTrack network and the Gnutella network. Software which
operates on these networks is:
Limewire and Bearshare who both use the Gnutella network.
Morpheus which uses all three networks. Kazaa and eMule which
operate on the eDonkey/Overnet networks and Ares with its own
network. Microsoft has its own system in WinMX, but it is
reputed to be complex and has its limitations.
There is also BitTorrent. This has a following among those
interested in sharing audio-visual files such as Movies and TV
shows. The original and official BitTorrent client tends to
monopolize a connection so that other internet business cannot
be carried during downloading though this has been resolved in
an alternative free version
BitTorrent is different form of P2P file sharing. With normal
systems such as the Gnutella system, you will typically
download a complete file from one source. In some cases the
software allows you to download the one file from a number of
contributing sources, thus speeding up the process. With
BitTorrent, on the other hand, you download different bits of
the file from a number of different sources (each file is split
into about 1,000 pieces). This not only speeds up the transfer
of large files around the network, but also allows you to
upload a file at the same time as you are downloading it.
Brian Dessent likens it to a book. A group of people round a
table each have different pages of a book. They want to get the
whole book, they let each other know what pages they have and
what they require. Eventually the pages are passed around till
a whole copy is obtained. If there are any pages missing,
someone is available with the whole book (called a ‘seed’) who
can supply what is missing to complete the book
Invented by programmer Bram Cohen, BitTorrent is therefore
different to any other kind of P2P network. It works
differently to other systems in its search facility: it has
none! Users must first carry out a web search to find the file
they require. There are , however, several BitTorrent search
engines on the web such as BTBot and TorrentSpy.
In addition to simultaneous downloading from multiples sources
which is common with most of the modern P2P applications,
eDonkey2000 also allows sharing of file segments where the file
size is larger than 9.8M. As with BitTorrent, this allows you to
upload a file while you are still downloading it so that the
more popular files can be very rapidly distributed round the
network. The problem with this is that sometimes the whole file
cannot be found, and you are left with part of the file which
you must complete at later date. This cannot happen with
traditional P2P systems such as Gnutella (e.g. Limewire and
Bearshare).
Free Downloading
The P2P networks such as Gnutella and BitTorrent are free. Many
companies will try to charge you for downloading the software,
but they are taking advantage of your ignorance. However, you
should be careful when selecting the free software.
The majority of free download programs comes with bundled
adware and spyware (also free of course!). An example of adware
is the pop-ups which appear on your screen and are devilishly
hard to remove. Sometimes the only way is to switch your
computer off and on again. Spyware sits on your computer and
send back messages to advertisers as to what you are doing or
watching so that ads can be customized to your preferences.
At its nastiest, spyware can copy your credit card and banking
details. It can also record keyboard clicks which allows all
sorts of Big Brother activities. Employers can find out what
you have been logging into all day, strangers can identify
number strings which could be credit card and bank account
details, including your passwords and login details. All very
nasty, so beware of free downloads.
Spyware and adware can be removed using software similar to
anti-virus programs. Beware of the free versions, however,
since they can put their own adware and spyware on which,
naturally, are not removed during the cleaning service. You are
better to use reputable paid software
However, back to download systems.
So, while most P2P software is available free, I would go for
the paid version. The payment normally has the option of a
one-off lifetime payment of up to around $39, though frequently
less. This covers maintenance of the site and 24/7 support. The
software itself is free. It also generally ensures that the
software is free of adware and spyware.
About The Author: Peter Nisbet is a graduate research chemist
with a great interest in audio-visual file formats and codecs,
and legal file sharing. Read about his views on the legal and
so called illegal aspects of P2P on http://www.legalandfree.com
If movies are your thing, try
http://www.online-free-movies.com
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