SMS Message Types

Text message types indicate how SMS should be delivered as well as the character encoding that should be used in delivering the message text to the mobile device. Additionally, the text message type affects the number of characters that count as one message page which in turn determines messaging cost taking into consideration the number of destinations to receive the message.

This section delves into text message types that can be specified as well as determination of number of message pages and total message costs.

Character Encoding

Character encoding defines which character sets are supported in a message text. Knowing the the character encoding for messages is very essential as any unsupported characters in the message text will be replaced with unknown or unexpected sequence of characters.

GSM-7/03.38 Character Encoding

The GSM 03.38 character encoding is the default character encoding for GSM messages. It is the standard character encoding used in GSM networks for SMS (Short Message Service), CB (Cell Broadcast) and USSD (Unstructured Supplementary Service Data). It uses 7-bit to store characters. As a result, not all characters are supported with this character encoding.

When sending messages with GSM 03.38 character encoding, it is important to know if characters in the message text are supported or not. Any characters which are not found in the GSM 03.38 character set and its extension will be replaced with unknown or unexpected character sequences.

Visit GSM 03.38 Character Encoding for a complete list of the supported characters for the GSM-7 character encoding.

Unicode Character Encoding

Unlike the GSM 03.38 character encoding which supports only few characters, the Unicode character encoding supports a wide range of characters. It supports the wide range of special characters and symbols found in many languages of the world.

The power of the Unicode character encoding to support many characters however comes at a cost. It uses more bits to store characters compared to the GSM 03.38 character encoding. As a result, only few characters are counted as 1 message page compared to the number of characters counted as 1 message page for GSM 03.38 character encoding. We take a look at these in our discussion of SMS message types.

A Look Into Text Message Types

We will now take a look at the individual text message types that can be set. These affect the number of message pages as well as messaging cost. A good understanding of these message types is therefore essential.

TEXT

The TEXT message type uses the GSM 03.38 character encoding to store characters when sending text messages to mobile handsets. A maximum of 160 characters count as a message page for SMS whiles 182 characters count as a message page for USSD messages. For any message text using TEXT message type, if the number of characters is greater than 160 characters, then the message will be treated as long or concatenated message and every 153 characters will be counted as a message page for SMS.

When the TEXT message type is set, SMS will by default be stored on the mobile device and the recipient can open the message to read it later.

UNICODE

The UNICODE text message type uses Unicode character encoding to store characters. With this message type, the maximum number of characters that count as a message page is 70 characters for SMS and 80 characters for USSD. For SMS, if the number of characters is greater than 70 characters, then the message will be treated as a long (concatenated) message and every 67 characters will be counted as message page.

It should be observed that UNICODE message type has fewer characters count for a message page relative to TEXT message type. The benefit however is that UNICODE message type supports many characters and symbols of a wide range of languages in the world. The choice of this message type will depend on the characters in the message text.

Like TEXT message type, when UNICODE message type is set, SMS will by default be stored on the mobile device and the recipient will have to open the message to read it later.

FLASH_TEXT

Message type FLASH_TEXT uses GSM 03.38 character encoding for sending flash messages. With flash messages, 140 characters is counted as 1 SMS page.

The major different between message types TEXT and FLASH_TEXT message types is that the FLASH_TEXT messages will not be saved to the mobile device by default. The message rather pops up on the mobile device for reading. Some modern mobile devices have the option to save flash messages to the device. If this is not supported on the mobile device, then the message cannot be re-displayed once it has been cleared from the screen.

FLASH_UNICODE

Setting the message type to FLASH_UNICODE indicates that the message should be sent as a flash message using the Unicode character encoding. This enables support for a wide range of characters and symbols in the message text.

With FLASH_UNICODE, the message will not be stored on the mobile device by default. It is displayed on the mobile device screen as in the case of FLASH_TEXT message type. If the recipient's device supports saving of flash messages, then the message can be saved to the mobile device otherwise the message cannot be re-displayed when the message is cleared from the screen.

Message Concatenation

Remember that there are a number of characters that count as a message page depending on the message type. This constraint should not be a limitation to sending long message contents. The constraint is overcome through message concatenation whereby different pages of the SMS are delivered and reassembled on the mobile device into one full message content. However, message concatenation works by sacrificing some character spaces in the preceding message page.

As an example, let's recall that message type TEXT has a maximum of 160 characters for a message page. However, if the length of the message text is more than 160 characters, then 153 characters is considered as message page. The reason is that the other character spaces that are sacrificed are used to set information that indicate to the mobile device that the message will need to be reassembled into one full content by concatenating the message page received with additional message pages that follow.

Character limitations for message page is therefore not a limitation for sending long messages. Messages that are long will be concatenated as one full message content on the mobile device.

Number of SMS Pages

This is the number of pages for SMS message text. As indicated earlier, there are number of characters that count as a message page depending on the text message type. For long messages, the message will be split into pages depending on the number of characters that make up message page for the specified message type.

To understand very well, let's think of writing in a book with several pages. First page may be full and we move to the next page. This is so with SMS. Messages can be split into several pages for delivery to the handset. The mobile device will however reassemble the different pages into one full message content.

The number of SMS pages is very important in determining the total cost of message. This is discussed next.

Credit Deduction

Knowing the credit deduction after sending a message is very important. This depends on the number of SMS pages, total number of destinations, and the price per SMS page.

For currency pricing model, the credit deduction will be the price per SMS page multiplied by the number of SMS pages and the total number of message destinations. Thus we can easily determine the total credit deduction with this simple formula

Credit Deduction = Price per SMS Page x Number of SMS Pages x Number of Destinations

In the case of volume pricing model, the credit deduction will be the number of SMS pages multiplied by the number of message destinations. That is,

Credit Deduction = Number of SMS Pages x Number of Destinations

With these formulas, the credit deduction for sending a message can be known even before submitting the message.