Short Message Service (SMS) is a service available on most digital mobile phones (and other mobile devices, e.g. a Pocket PC, or occasionally even desktop computers) that permits the sending of short messages (also known as text messages, or more colloquially SMSes, texts or even txts) between mobile phones, other handheld devices and even landline telephones. Other uses of text messaging can be for ordering ringtones, wallpapers and entering competitions. There are also many services available on the Internet that allow users to send text messages for free.
History
As with most other services and modules of functionality of the GSM system, no individual can claim the fatherhood of SMS. The idea of adding text messaging to the services of mobile users was latent in many communities of mobile communication services at the beginning of the 1980s.
Experts from several of those communities contributed in the discussions on which should be the GSM services. Most thought of SMS as a means to alert the individual mobile user, e.g. on incoming voice mail, whereas others had more sophisticated applications in their minds, e.g. telemetry. However, few believed that SMS would be used as a means for sending text messages from one mobile user to another.
Technical side
Messages are sent via a store-and-forward mechanism to a Short Message Service Centre (SMSC), which will attempt to send the message to the recipient. If the user is not reachable at a given moment, the SMSC will save the message. Later when the user is reachable, the SMSC will retry the delivery process.
Both Mobile Terminated (MT), for messages sent to a mobile handset, and Mobile Originating (MO), for those that are sent from the mobile handset, operations are supported. Message delivery is best effort, so there are no guarantees that a message will actually be delivered to its recipient and delay or complete loss of a message is not uncommon, particularly when sending between networks.
Users may choose to request delivery reports, which can provide positive confirmation that the message has reached the intended recipient, but notifications for failed deliveries are unreliable at best.
The SMS specification has defined a way for an external Terminal Equipment, such as a PC or Pocket PC, to control the SMS functions of a mobile phone. The connection between the Terminal Equipment and the mobile phone can be realized with a serial cable, a Bluetooth link, an infrared link, etc. The interface protocol is based on AT commands. Common AT commands include AT+CMGS (send message), AT+CMSS (send message from storage), AT+CMGL (list messages) and AT+CMGR (read message).
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