by Asela Bandara

Numerous technologies are used in different contexts in the mobile computing to exchange data, information within their mobile entities as well as some other static computer system. Mobile phones have become very important components in mobile computing applications, as many of the recent applications are integrated with mobile solutions. Thus internationally standardized data/information exchanging strategies are often used in almost all of these business solutions.

As mobile phones acquire more attention in the mobile for computer systems world, GSM technology or one of its enhancements is been used in providing data synchronization to the high-end enterprise applications with its mobile customers or staff. SMS (Short messaging service) is the ancestor for most of the currently used its’ own improvements.  There are few concerns to be known by the people who are going to use this technology for their applications or services.

SMS (Short Message Service)

Figure 1

[http://www.smsest.com/images/sms-diag.jpg]

SMS stands for Short Message Service.  What is simply put, it is a method of communication that sends text between cell phones, or from a PC or handheld to a cell phone. SMS first appeared in Europe in 1992. It was included in the GSM (Global System for Mobile Communications) standards right at the beginning. Later it was ported to wireless technologies like CDMA and TDMA.

As suggested by the name "Short Message Service", the data that can be held by an SMS message is very limited. One SMS message can contain at most 140 bytes (1120 bits) of data, so one SMS message can contain up to:

· 160 characters if 7-bit character encoding is used. (7-bit character encoding is suitable for encoding Latin characters like English alphabets.)

· 70 characters if 16-bit Unicode UCS2 character encoding is used. (SMS text messages containing non-Latin characters like Chinese characters should use 16-bit character encoding.)

SMS text messaging supports languages internationally. It works fine with all languages supported by Unicode, including Arabic, Chinese, Japanese and Korean. Besides text, SMS messages can also carry binary data. It is possible to send ringtones, pictures, operator logos, wallpapers, animations, business cards and WAP configurations to a mobile phone with SMS messages.

Traditional SMS Architecture

Figure 2

[http://www.dialogic.com/products/signalingip_ss7components/docs/10171_SMS_Success.pdf]

GMSC : Gateway Mobile [service] Switching Center

HLR : Home Location Register

MSC     : Mobile Service Switching Center

SMS     : Short Messaging Service

SMSC   : Short Messaging Service Center

Figure 1 illustrates the traditional SMS architecture in which every message was stored and forwarded to its destination using a Short Message Service Center (SMSC). The SMSC included a gateway to all the content stored on a network, and C, D, and E signify standard GSM interfaces.

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.

Figure 3

[http://billmonk.files.wordpress.com/2007/04/sms_choose1.jpg]

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.

But how do SMS messages actually get to your phone?

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.

 Figure 4

[http://www.developershome.com/sms]

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 certain number 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 or music 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 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).

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