Transferring files in Internet is one of the many facilities Internet provides us. You may be aware that files can be downloaded using HTTP or FTP. Now you can use the 'Bit Torrent' protocol to send and receive files.
Bit Torrent protocol functions in a peer-to-peer method. One person can enter into another person's computer and send are receive files. That is why this type of computers are called 'Peer's. But there is a server required to make all these computers work together. This server is called 'Tracker'.
The tracker just monitors the connections between the peers. Other than that the tracker does not know which files are being transferred between peer computers. Therefore the tracker needs a very little bandwidth to monitor a huge number of peers.
When someone uploads a file from his computer to another computer, he can also download a file from another computer simultaneously
How Bit Torrent works?
Let us see how Bit Torrent works with an example. A few people are seated in a room. Let us consider that all these people need a complete copy of all the pages in a book. Person A says that he has pages 1-15, 29, 36-40, 55, 74-89 and 94-100. Let us assume that these pages are not with persons B, C, D, E and F. Immediately they contact A and get a copy of all these pages. Now person B announces that he has pages 17-24,32,34,41-50,57,60-70 and 90-93. Then the rest of the persons will get copies of these pages from B.
Likewise all the persons announce the pages each of them have. Those who do not have a page they will get the page from the respective persons.
Very soon, all the persons in the room will have all the pages of the book. In that group a person named 'K' will be present. He will have all pages of the book. You may ask why not all A,B,C,D and E get all pages for K directly. But if all of them connect to K at the same time then they can just be receivers not senders.
Instead, if A,B,C,D and E share pages from each other then they can be both senders and receivers.
Therefore if everyone needs everything then everyone should be both receivers and senders. This is exactly the method used by Bit Torrent.
K is called 'Seed' in Bit Torrent.