HOW SMS WORKS????

Just 
when we're finally used to seeing everybody constantly talking on their 
cell phones, it suddenly seems like no one is talking at all. Instead, 
they're typing away on tiny numerical pads, using their cell phones to 
send quick messages. SMS, or text messaging, has replaced talking on 
the phone for a new "thumb generation" of texters. 




In this article, we'll find out how text messaging works, explore 
its uses and learn why it sometimes takes a while for your text message 
to get to its recipient. 




SMS stands for short message service. Simply put, it is a method of 
communication that sends text between cell phones, or from a PC or 
handheld to a cell phone. The "short" part refers to the maximum size 
of the text messages: 160 characters (letters, numbers or symbols in 
the Latin alphabet). For other alphabets, such as Chinese, the maximum 
SMS size is 70 characters. 




But how do SMS messages actually get to your phone? If you have read 
How Cell Phones Work, you can actually see what is happening. 




Even if you are not talking on your cell phone, your phone is 
constantly sending and receiving information. It is talking to its cell 
phone tower over a pathway called a control channel. The reason for 
this chatter is so that the cell phone system knows which cell your 
phone is in, and so that your phone can change cells as you move 
around. Every so often, your phone and the tower will exchange a packet 
of data that lets both of them know that everything is OK. 




Your phone also uses the control channel for call setup. When 
someone tries to call you, the tower sends your phone a message over 
the control channel that tells your phone to play its ringtone. The 
tower also gives your phone a pair of voice channel frequencies to use 
for the call. 




The control channel also provides the pathway for SMS messages. 
When a friend sends you an SMS message, the message flows through the 
SMSC, then to the tower, and the tower sends the message to your phone 
as a little packet of data on the control channel. In the same way, 
when you send a message, your phone sends it to the tower on the 
control channel and it goes from the tower to the SMSC and from there 
to its destination. 




The actual data format for the message includes things like the length 
of the message, a time stamp, the destination phone number, the format, 
etc. For a complete byte-by-byte breakdown of the message format, 




  





SMS History 

SMS was created during the late 1980s to work with a digital 
technology called GSM (global system for mobile communications), which 
is the basis for most modern cell phones. The Norwegian engineers who 
invented it wanted a very simple messaging system that worked when 
users' mobile phones were turned off or out of signal range. Most 
sources agree that the first SMS message was sent in the UK in 1992. 




As SMS was born in Europe, it's not surprising that it took a 
little longer to make its way to the United States. Even today, texting 
enjoys much greater popularity in Europe, though its stateside use is 
on the rise. A July 2005 study found that 37 percent of U.S. mobile 
phone owners had sent or received at least one text message in the 
previous month [ref]. 




SMS Attacks 


Recently it has been suggested that SMS messages could be used to 
attack a cell phone system. The basic idea is very simple. If a large 
number of SMS messages were sent by computers to phones in a small 
geographical area (like a city), these messages would overwhelm the 
control channels and make it impossible for the cell phone system to 
set up calls. Now that cell phone providers know about the possibility 
of this threat, they can design systems to throttle messages coming 
from the SMSC onto the network. 





Why 160 Characters? 

SMS was designed to deliver short bursts of data such as numerical 
pages. To avoid overloading the system with more than the standard 
forward-and-response operation, the inventors of SMS agreed on a 
160-character maximum message size. 




But the 160-character limit is not absolute. Length limitations may 
vary depending on the network, phone model and wireless carrier. Some 
phones don't allow you to keep typing once the 160-character limit is 
reached. You must send your message before continuing. However, some 
services will automatically break any message you send into chunks of 
160 characters or less. So, you can type and send a long message, but 
it will be delivered as several messages. 




lternatives to SMS 


Alternative messaging services allow for more elaborate types of 
messages. With EMS (Enhanced Messaging Service), you can send formatted 
text, sound effects, small pictures and icons. MMS (Multimedia 
Messaging Service) allows you to send animations, audio and video files 
in addition to text. If your mobile phone is EMS- or MMS-enabled, you 
can use these standards just as you would SMS. However, the cost per 
message will be higher. 




Another alternative to using SMS is using an instant messaging 
program, such as AOL IM, on your cell phone. This can be in the form of 
software that's pre-installed on your phone, or you can use WAP 
(Wireless Application Protocol) to access the Internet and sign into 
your IM account. WAP is a protocol that gives you small, simplified 
versions of web pages that are easily navigable on your mobile phone or 
PDA (check out How WAP Works for more information). You can use it to 
send instant messages or actual e-mails from your phone. 




A common complaint about SMS is its inefficient delivery structure 
-- when the message center is backed up, messages take longer to reach 
their destination. To make message delivery faster, networks are using 
more new next-generation technologies such as GPRS (General Packet 
Radio Service).