HowStuffWorks SMS

7/28/2019 HowStuffWorks SMS

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How SMS WorksbyJennifer HordBrowse the articleHow SMS Works

Introduction to How SMS Works

Just when we're finally used to seeing everybody constantly talking on

theircell 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 itsuses and learn why it sometimes takes a while for your text message

to get to its recipient.

SMS stands forshort message service. Simply put, it is a method of

communication that sends text between cell phones, or from aPCor

handheldto 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 readHow Cell Phones Work, you can

actually see what is happening.

SMS Attacks

Recently it has been suggested that SMSmessages could be used to attack a cell phonesystem. The basic idea is very simple. If a largenumber of SMS messages were sent bycomputers to phones in a small geographicalarea (like a city), these messages wouldoverwhelm the control channelsand make itimpossible for the cell phone system to set upcalls. Now that cell phone providers know about

the possibility of this threat, they can designsystems to throttle messages coming from theSMSC onto the network.

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

Text messaging has replacedtalking on the phone for someusers. See morecell phone

pictures.
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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, seethis page.

Why 160 Characters?SMS was designed to deliver short bursts of data such asnumerical pages. To avoid overloading the system with more thanthe standard forward-and-response operation, the inventors ofSMS agreed on a 160-character maximum message size.

But the 160-character limit is not absolute. Length limitations may
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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 asseveral messages.

Advantages of SMS

SMS has several advantages. It is more discreet than aphoneconversation, making it the ideal form for communicating when youdon't want to be overheard. It is often less time-consuming to send atext message than to make a phone call or send an e-mail. SMSdoesn't require you to be at your computer likee-mailandinstantmessaging(IM) do -- although some phones are equipped for mobilee-mail and IM services. SMS is also a convenient way for deaf and

hearing-impaired people to communicate.

SMS is a store-and-forward service, meaning that when you send a

text message to a friend, the message does not go directly to your

friend's cell phone. The advantage of this method is that your friend's

cell phone doesn't have to be active or in range for you to send a

message. The message is stored in the SMSC (for days if necessary)

until your friend turns his cell phone on or moves into range, at which

point the message is delivered. The message will remain stored on

your friend'sSIM carduntil he deletes it.

In addition to person-to-person messages, SMS can be used to send

a message to a large number of people at a time, either from a list ofcontacts or to all the users within a particular area. This service is

called broadcasting and is used by companies to contact groups of

employees or by online services to distribute news and other

information to subscribers.

In a 2004 University of Plymouth study on the psychology of SMS users, researchers found that mobile

phone users were primarily either "texters" or "talkers" [ref]. Compared to the talkers, the texters sent

nearly double the number of SMS messages and made less than half as many voice calls per month. The

texters preferred SMS to voice calls for its convenience as well as for the ability to review a message

before sending it.

Companies have come up with many uses for the service beyond just your typical person-to-personmessage. Because SMS doesn't overload the network as much as phone calls, it is frequently used by TV

shows to let viewers vote on a poll topic or for a contestant. As a promotional tool, wireless carriers put up

giant screensat concerts and other large-scale events to display text messages from people in the

audience.

SMS HistorySMS was created during the late 1980s to work with a digital
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technology calledGSM(global system for mobilecommunications), which is the basis for most modern cell phones.The Norwegian engineers who invented it wanted a very simplemessaging system that worked when users' mobile phones wereturned off or out of signal range. Most sources agree that the firstSMS 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].

You can use text messaging subscription services to get medication reminders sent to your phone, along

with weather alerts, news headlines or even novels broken into 160-character "chapters." Internetsearch

enginessuch as Yahoo! and Google have short messaging services that enable users to get information

such as driving directions, movie showtimes or local business listings just by texting a query to the searchengine's phone number. Social networking services such asDodgeballuse SMS to alert people who live

in big cities when their friends or crushes are nearby. The possibilities for integrating SMS into your

lifestyle seem endless.

Next, we'll discuss the disadvantages of SMS and look at some alternative communication technologies.

SMS Criticism and Alternatives

Despite their popularity, short messaging services have received some

criticism. Here are a few of the disadvantages of SMS:

You have to pay for it. Most wireless plans charge for a certainnumber of text messages a month. Some only charge for user-

originated messages, while others charge for incoming

messages as well. If you exceed your message allowance, you

may be charged 10 cents per message, and those little charges

can add up.

Speedy message delivery is not guaranteed. During periods of

high traffic, it might be minutes or even hours before a message

gets through.

It's strictly for sending text messages. SMS does not support

sending pictures, video ormusic files.

Alternatives 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 yourmobile phoneis EMS- or MMS-enabled, you can use these

standards just as you would SMS. However, the cost per message will be higher.

SMS in the NewsBecause of the impersonalnature of SMS, it raises certainquestions of etiquette -- namely,what kind of information is OK tosend in a text instead ofdelivering it in person?Recently, several people havesought legal action after theywere fired or notified ofdivorceproceedings via SMS.

Broadcast text messages have

been used to rally political

activists in Beijing and to

mobilize young people for riots

in Belfast. Recently, a contestpitted the efficiency of SMS

against Morse code (the Morse

coders won).
http://electronics.howstuffworks.com/question537.htmhttp://electronics.howstuffworks.com/question537.htmhttp://electronics.howstuffworks.com/question537.htmhttp://framed.htm/?parent=sms.htm&url=http://www.clickz.com/stats/sectors/wireless/article.php/3530886http://framed.htm/?parent=sms.htm&url=http://www.clickz.com/stats/sectors/wireless/article.php/3530886http://framed.htm/?parent=sms.htm&url=http://www.clickz.com/stats/sectors/wireless/article.php/3530886http://computer.howstuffworks.com/search-engine.htmhttp://computer.howstuffworks.com/search-engine.htmhttp://computer.howstuffworks.com/search-engine.htmhttp://computer.howstuffworks.com/search-engine.htmhttp://framed.htm/?parent=sms.htm&url=http://www.dodgeball.com/http://framed.htm/?parent=sms.htm&url=http://www.dodgeball.com/http://framed.htm/?parent=sms.htm&url=http://www.dodgeball.com/http://computer.howstuffworks.com/mp3.htmhttp://computer.howstuffworks.com/mp3.htmhttp://computer.howstuffworks.com/mp3.htmhttp://electronics.howstuffworks.com/cell-phone.htmhttp://electronics.howstuffworks.com/cell-phone.htmhttp://electronics.howstuffworks.com/cell-phone.htmhttp://people.howstuffworks.com/divorce.htmhttp://people.howstuffworks.com/divorce.htmhttp://people.howstuffworks.com/divorce.htmhttp://people.howstuffworks.com/divorce.htmhttp://electronics.howstuffworks.com/cell-phone.htmhttp://computer.howstuffworks.com/mp3.htmhttp://framed.htm/?parent=sms.htm&url=http://www.dodgeball.com/http://computer.howstuffworks.com/search-engine.htmhttp://computer.howstuffworks.com/search-engine.htmhttp://computer.howstuffworks.com/search-engine.htmhttp://framed.htm/?parent=sms.htm&url=http://www.clickz.com/stats/sectors/wireless/article.php/3530886http://electronics.howstuffworks.com/question537.htm


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Another alternative to using SMS is using aninstant messagingprogram, 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 outHow WAP Worksfor more information). You can use it to send instant messages or

actuale-mailsfrom 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).

To learn more about SMS and other forms of mobile communication, check out the links on the following

page.

Lots More Information

Related HowStuffWorks Articles

How Cell Phones WorkHow Cell-phone Viruses Work

How Ringtones Work

Cell Phone Buying Guide

How Radio Works

How Routers Work

How Instant Messaging Works

How E-mail Works

How WAP Works

What does GSM mean in a cell phone?

What is a packet?

More Great Links

SMS Tutorial

160 Characters

Textually.org

Dodgeball

Sources

Barkhuus, Louise and Anna Vallgarda. "Saying it All in 160 Characters: Four Classes of SMS

Conversations."

IT University of Copenhagen, April 2004.

http://www1.itu.dk/graphics/ITU-

library/Internet/Forskning/Technical_Reports

/ITU-TR-2004-45.pdf

Burns, Enid. "Teens, College Students Are Most Active Cell Phone Users."

Click Z Network, August 29, 2005.

http://www.clickz.com/stats/sectors/wireless/article.php/3530886

Clements, Tom. "SMS - Short But Sweet."

http://developers.sun.com/techtopics/mobility/midp/articles/sms
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Coll, Steve. "In the Gulf, Dissidence Goes Digital." Washington Post, March 29, 2005.

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