SMS technology overview

This guide introduces the SMS technology. It aims to define the basic concepts and helps the understanding of how the SMS technology works and what it is used for. If you use SMS, but do not know much about how it works, this is the place to start.

What is SMS?

The Short Message Service (SMS) is the text messaging service component of mobile telephone networks. It uses standardized communication protocols to enable mobile devices to exchange short text messages.

Where is SMS used?

SMS is used on Android, IOs and legacy mobile phones. These are the terminal devices that humans use to send and receive text messages. SMS is also used by applications that run on computers. These applications are used to send and receive messages automatically. When SMS is used on computer an SMS Gateway system is installed on a Windows or Linux PC.

The history of SMS

SMS was first defined for the Global System for Mobile Communications (GSM) networks. The first test SMS message was sent in 1992 and it commercially rolled out to many cellular networks that decade. SMS became hugely popular worldwide as a way of text communication. By the end of 2010, SMS was the most widely used data application, with an estimated 3.5 billion active users, or about 80% of all mobile phone subscribers at the time.

The limitations of SMS technology

The SMS protocols allows users to send and receive 140 bytes (8-bit octets) of data in one SMS message. By default, this data is used to deliver text containing characters of the SMS alphabet, which is a 7 bit alphabet. If a text message is sent using the 7-bit SMS alphabet, 160 characters can be included in a single SMS message.

To support longer SMS messages a technology called multipart messaging was developed. When this technology is used, the sender splits the content of the message and delivers the segments of 140 bytes in several SMS messages. The recipient then puts together these messages segments to get the original content. These procedures are called SMS Segmentation and Reassembly (SAR).

The original 7-bit SMS alphabet was not fit for international users, because it could not carry non-Latin characters, so Unicode messaging was introduced. In Unicode messaging 2 bytes (16 bits) are used to carry each character. Because of this only 70 Unicode characters fit in an SMS message. This means sending long messages using the Unicode character set is generally more expensive. On the other hand, these messages can carry Chinese, Arabic, Hebrew and other characters.