Orangeman Burns - Sriram Sridharan's Blog

Imagine this: You're on the way to an important meeting. You suddenly realize that you forgot to transfer your Powerpoint presentation onto your laptop or pendrive. What do you do?

One obvious solution is to ask your secretary to upload the file onto a file hosting website like Rapidshare or Megaupload so that you can download it from your mobile phone. The problem is that HTTP transfers on mobile phone connections are notoriously unstable for transfers more than 10-15 KB. Even more so when on the move. This is where BitTorrent redeems itself. You might know it as "Torrent" or "BT". BitTorrent has a very good error checking mechanism and can pause, stop and resume file transfers without any data loss.

BitTorrent is a technology that is specifically meant for fast and shared transfer of files also known as P2P(Peer to Peer) Sharing. While the technology behind BitTorrent is vast and not relavant right now, let me share with you the salient points. The explanations given here are highly simplified for content and space.

• The person with a full copy of the file is called a seeder.
• A person attempting to download the file is called a leecher.
• To initiate the download of the file from a seeder, you need a torrent file. Simply put, a torrent file acts like an index of all the computers who have a copy of the file. It also contains a link to the torrent tracker.
• A torrent tracker is a service run by a server that enables communication between the peer and seeder computers.

In our previous forgetful businessman analog, the secretary/collegue who has the file is seeder. You are the leecher.

To transfer the file from your office to your mobile phone via BitTorrent, you'll need the following:

1. A BitTorrent client on your computer. A simple freeware client that i recommend is uTorrent. The file itself is less than 300KB in size. You can download it here: http://www.utorrent.com/download.php
2. A BitTorrent client on your mobile phone. If you have a Symbian S60 V3 or V5 phone, get Symtorrent. For any other phones that support Java based applications[Most of the modern phones on the market do] use MobTorrent . To use MobTorrent, your phones must support CLDC 1.1, MIDP 2.0 and JSR 75. To know if your phone does support these specifications, visit your manufacturer's website. If you have a S60 V2 phone that doesn't support the above applications, give WizBit a try. Though it is no longer supported, it does work on old phones like Nokia 6600.

3. A Data plan or a GPRS enabled connection on your SIM card. Charges typically are about 1 paise per KB but don't hold me to it. A typical resume is about 50KB. So to transfer the file, you'll be charged about 50 paise.

4. An account with a BitTorrent tracker. I personally recommend and use ThePirateBay but you can use any other tracker.

The screenshots and procedure I will be following in this guide are from uTorrent and Symtorrent. If you are going to use other clients, the steps you need to follow will differ a little.

What your secretary/collegue needs to do:
1. Open uTorrent.
2. Go to File >> Create New Torrent or simply hit Ctrl-N.

3. Browse to the directory where the file in question is located, and select it.
4. Add the tracker urls for the tracker site you selected. If you're using ThePirateBay, use the following trackers:

http://open.tracker.thepiratebay.org/announce
http://tracker.thepiratebay.org:80/announce
udp://tracker.thepiratebay.org:80/announce

5. Enter a comment if you need to, check the "Start seeding" option and click the "Create and save as" button.


6. The created torrent file will have started seeding in the uTorrent window.


7. Go to the torrent tracker site and login and select upload torrent.
8. Upload the torrent by filling in the requisite details. The screenshot shows form for uploading a torrent on ThePirateBay.

9. When you're done, go to the torrent page you've been given and download the torrent file from the site.
10. Send the torrent file via email or a file sharing site. A simple filesharing site I recommend is drop.io.
11. This part of file sharing is done!
Note: Since the created torrent file is about 1KB for a small file, downloading the torrent file via HTTP does not pose any problems. Also remember to keep uTorrent running until the file is downloaded on the mobile phone.

What you need to do:
1. Download the .Torrent file that your secretary/colleague sends you and save it on your phone.
2. Open Symtorrent.

3. Browse, navigate to the torrent file and open it.


4. The downloading process will automatically start.

5. Once the download status reaches 100%, press stop sharing and the file transfer is done.


6. Instruct your secretary/colleague to delete the file from the tracker and exit uTorrent.
7. You've successfully transferred your file.


Since the files that uploaded in the tracker are open for public download, it's recommended that you encrypt your files with atleast a 256 bit key. An easy way of doing it is to use WinZip or WinRar where this functionality is built in. Also do not forget to delete the upload from the tracker site.

For a more detailed readup on filesharing, P2P and BitTorrent checkout my earlier posts:
http://www.sriraminhell.com/2007/08/p2p-brief-introduction.html
http://www.sriraminhell.com/2007/08/peer-to-peer-ii-bit-torrent.html

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