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Long messages and Concatenation
Applications that require more than 160 characters of information transfer can use the message_payload parameter which can hold up to a maximum of 64K. However, the maximum size supported is SMSC dependent and the application should take this into account.
Another available method for sending more than 160 characters of information is the GSM concatenation mechanism. With concatenation it is possible to send several separate short messages to a mobile station and to display them as one message when delivered.
Concatenation is realized at the mobile handset; multiple separated received messages are stringed together and displayed asif it was one single short message. The mobile handset is able to do this, as all involved sent messages contain an additional information field that provides information needed for connecting them. Up to a maximum of 255 short messages can be concatenated this way.
Concatenation is provided via method:
- GSM User data headers
| Byte | Value | Description |
|---|---|---|
| 01 | 00 | Information Element Identifier: Concatenated short message, 8bit reference number |
| 02 | 03 | Information Element Data Length (always 03 for this UDH) |
| 03 | A4 | Information Element Data: Concatenated short message reference, should be same for all parts of a message |
| 04 | 03 | Information Element Data: Total number of parts |
| 05 | 01 | Information Element Data: Number of this part (1/3) |
Example of a multipart message consisting of 3 parts containing 300 bytes:
SMS 1 User Data: 00 03 A4 03 01 [ 135 bytes of message data ]
SMS 2 User Data: 00 03 A4 03 02 [ 135 bytes of message data ]
SMS 3 User Data: 00 03 A4 03 03 [ 30 bytes of message data ]