Long SMS

English | Log IN

Multipart SMS messaging

By design, SMS is developed to send up to 140 bytes of user data. All user data is send in the 'User Data' part of the SMS packet.
Because SMS text messages are encoded using 7-bit characters you can send up to 160 characters in a single SMS message.
When sending Unicode text, you can only send 70 characters per single SMS message.

It is however possible to split up text and data messages and send them using multiple SMS messages.
The receiving party will be able to combine the messages to the original message. This is called Segmentation and Reassembly (SAR).
When sending multipart SMS messages you will be charged for every single SMS message sent.

Sending Multipart Messages through a SMPP Server

To send enhanced content, a so called user data header (UDH) is added add the beginning of the user data block of the SMS.
When using an UDH, there is less data left for user data in the User Data field (140 - length of UDH).

An UDH can be used to send multipart messages, smart messaging (ringtones, WAP push, pictures etc), voicemail indications and other services.
In this article we will only discuss the use of UDH to send multipart text messages.

The UDH for message concatenation will only take 5 bytes, so there are 135 bytes left for the user data.
When sending concatenated text messages, you can send 153 characters when using 7-bit text, when using Unicode 67 characters per part.

To send a multipart message through a SMPP server, you have to add the same UDH as above.
Some providers allows you to send multipart messages without the need to encode this header.
This is done using the so called TLV paramaters which are extra options which can be used from version 3.4 of the SMPP protocol.

sar_msg_ref_num, sar_gegment_seqnum and sar_total_segments

These parameters are sent together with the submit_sm packet. You have to set this values, but you do not have to add the UDH to the
messagedata field. You only have to split the message into parts and reserve 5 bytes per messagedata field, because the SMPP provider will
add the UDH header for you.

OTA bitmap SMS, binary

The OTA or Over The Air Bitmap was defined as part of the Smart Messaging Specification, to send pictures as a series of one or more concatenated SMS text messages. The format has a maximum size of 255x255 pixels. It is very rare for an OTA bitmap to measure anything other than 72x28 pixels (for Picture Messages) or 72x14/72x13 (for Operator Logos). The specification contains a byte of data to be used for indicating a multicolor image. This was to future-proof the standard, but the advent of Multimedia Messaging meant it never got to implementation.

An OTA bitmap is used for various SMS formats; Operator logos, CLI icons, Picture Messages, and Downloadable Profiles. In most phones the maximum size of the operator logo and the CLI icon is 72 x 14 pixels, while the maximum size of the picture message and the screen saver is 72 x 28 pixels. An OTA bitmap consists of a bitmap header and bitmap data. The size of the bitmap is specified in the header.

A typical OTA bitmap (72 x 14 pixels) header is: 00480E01
00     Info field
48     Width of the bitmap is 72 pixels
0E     Height of the bitmap is 14 pixels
00     Number of colors or grey shades (only one color)

The image data is located after the header information and is encoded as follows. Each semi-octet in the OTA bitmap presents 4 pixels in the original bitmap. As one row takes 18 semi-octets, the whole 72 x 14 (operator logo and CLI icon) bitmap takes 18 x 14 = 252 semi-octets = 126 octets. Including the picture message and the screen saver, the entire 72 x 28 size bitmap takes 18 x 28 = 504 semi-octets = 252 octets. For example, if the first four pixels of the image are 1010 (1 - black, 0 - white), the first semi-octet of the OTA bitmap data is hex A.

Reference

Informations: www.activexperts.com