What on earth is? - Text messaging

Have you experienced the joy of text? Already, that seems like an overused line, yet the technology to which it refers only started making headlines a couple of years ago. We're talking about SMS, or Short Message Service.

Better known as text messaging, SMS is the technology that enables millions of mobile phone users to communicate with abbreviated alacrity. As a consequence, the oft-awkward immediacy, and expense, of making voice calls has given way to this cheap and cheerful chat form. Why broadcast plans for a romantic weekend on the bus ride home when you can tap-chat with your loved one in near-silence?

The first SMS was sent in 1992, when, to test the fledgling system, Vodafone engineers sent a note from a computer to an early GSM mobile phone. The first commercial text-messaging service went live in 1994 but only a tiny number of communiques were sent out in that first year. Indeed, SMS went all but unnoticed by consumers until the second half of the decade. Then, it took off - and how.

From just a few thousand messages sent in 1997, SMS traffic levels rose exponentially. The latest figures from the GSM Association show that the daily number of text messages buzzing around the world has grown to a total of one billion. If you need that spelled out, an average 1,000,000,000 text messages worldwide are sent every day.

Despite its success, the future of the text message is in doubt. As mobile phone owners migrate to the next generation of handsets and operator networks, the short-message service's limitations will become increasingly obvious.

Will users put up with the restriction of truncated, text-only messages when advanced phones will allow the preparation of colourful emails with multimedia attachments? It's unlikely to happen overnight, but the text message looks destined to go the same way as Telex and fax machines before it.

THE BASICS

Only two things are needed to get text messaging: a GSM mobile phone and a flexible thumb. The latter is used to tap out the content of your messages, while the former transmits them.

The limitations of SMS technology mean that text messages are restricted to 160 characters in length or less and the text-entry method depends on the type of phone used. Basic handsets oblige users to exercise their digits on the numeric pad, using individual buttons to cycle through sections of the alphabet to reach the required letter. Typically, for example, a phone's number 2 key is used to rotate through the letters A, B and C.

More advanced phones offer predictive text input, or T9, named after a word-prediction algorithm created by a company called Tegic. This system eliminates much of the irksome key-bashing by second-guessing intended words as they're spelled out on the keypad.

From the user's perspective, selecting the phone's Send option and entering the recipient's mobile phone number concludes message transmission. Behind the scenes, though, much more needs to happen.

THE SCIENCE

SMS is a 'store-and-forward' technology. When a phone's Send function is initiated, the handset dials the number of the network operator's Short Message Service Centre (SMSC). This is usually pre-programmed into the SIM card.

Phone and SMSC then perform an electronic handshake; afterwards, the handset is given access to a slow-speed data channel (SSDC). The phone uses this to deliver the content of its text-message area to the SMSC.

Most networks reserve seven data bits per alphanumeric character, which is enough for 160 characters. In territories communicating in ideograms - notably China - more data bits are required to represent each symbol, reducing the SMS length to just 70 characters.

The SMSC's computer system attempts repeatedly to deliver a received text message to the required destination number. If the intended recipient remains unavailable to the network for the length of a preset expiry period - typically one week - the message may be erased and lost forever.

WHY YOU NEED TO KNOW ABOUT IT

Text messaging is already hugely popular and if you're not aware of its existence, you're missing out on a world buzzing with stealth communications.

While email correspondence generally requires a computer or pocket organiser of some kind, anyone in possession of a GSM mobile phone can communicate using SMS. Mobile phone network and talk plan permitting, you'll be able to send and receive messages from almost any country, on all continents.

SMS is already a communications mass-medium. But success like this has its drawbacks. With such a wide and easily accessible audience, the technology has attracted the unwanted attentions of advertisers. Text-message commercials are already prevalent and likely to flourish in the future.

Meanwhile, SMS has been identified as a potential outlet for those with altogether more sinister motives. In January, a Dutch researcher demonstrated the feasibility of SMS-borne computer virus-style code by sending pernicious text messages to various Nokia mobile phone models, thus rendering them unusable.

JARGONBUSTER

SIM Subscriber Identity Module. The smartcard used by all digital mobile phones. The SIM card carries the user's identity and phone number for accessing the network. It also is used for storing the user's personal phonebook and text messages.

GSM Global System for Mobile communications. The digital mobile phone system used in the UK and many other countries.