Sunday, January 17, 2010

Haiti and SMS

I didn't realize blogging on a regular basis would be such a challenge!  At the time I started this note, some reports said over $8 million had been raised for Haiti from text messaging the string "HAITI" to 90999.  Think about that, at $10 per text message, that's more than 800 thousand text messages.  No doubt the numbers are much higher now.  This has been done before, as similar mechanisms were in place for the Tsunami and Katrina.  What a great way to help out...  just think how much money would be raised if everyone with a cell phone jumped in... there are over 270,000,000 cell phone users in the United States alone, that's a lot of money!

The mechanism used to raise the money, SMS (Short Message Service), is at minimal cost to the providers, who send the SMS data on a control channel.  This is a nice profit margin for them, some of whom are charging 15 cents for each send and receipt.  The control channel is in place to track which tower your cellphone is connected to, so your phone can change cells as you move around... messages are traveling on the control channel at periodic intervals even when your phone is not in use, as this packet exchange lets both the tower and the phone obtain the service status.  Since the control channel is also used to set up a phone call, care is taken to make sure SMS messages don't overwhelm the channel.  SMS messages may be delayed or throttled to make sure voice calls go through...

The SMS message itself contains up to 140 bytes (1120 bits) of data - this takes care of the 160 characters allowed in your text message.  Confused?  SMS uses 7-bit characters, instead of 8-bit, which leaves 128 possible character values instead of the normal 256. So 1120bits/7bits = 160 characters.  There is a bit of processing to convert the 7-bit data into 8-bit (octets), here's an example showing how the message "hellohello" is converted... as you can see there's a lot going on when an SMS is sent!  I'll spare you the details on the message encoding and other header data necessary to make sure the message gets to it's designated receiver.

Tip : The research I did across the net was made a lot easier with iCyte.com's research tool.  It's a great way to do research and installs as an add-on to Firefox or Internet Explorer.  Create a free account and start a project.  If you come across a page you want to keep for reference, just add it to your project with a simple click. It's more powerful than organizing bookmarks.  iCyte enables you to highlight and save text on any webpage, allowing you to recall the most relevant information. You can save sections of webpages or the whole thing.  Webpages you "Cyte" are saved forever on the server, letting you return to your research even if the webpage has been deleted or modified.  The sites I used included howstuffworks.com - a valuable site to learn the details on just about anything.

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