Concatenated SMS
Single SMS messages have a limit of 160 characters so for longer SMS messages, a strategy of concatenation should be employed. Concatenation allows sending multiple SMS messages which are then joined as a single long SMS on the destination device.
Specifying that SMS messages should be concatenated via the API is done using the udh parameter which stands for User Data Header.
User Data Header (UDH)
User Data Headers (UDH) are a short strings of bytes at the start of an SMS used to indicate the handling of the content of an SMS. Specifying that messages should be concatenated and in what order may be done in these headers.
The following two API calls would concatenate two SMS messages into one on the destination device:
First SMS UDH value:
Second SMS UDH value:
These UDH values are read as follows:
2 byte IEI
For an IEI of 08, the SMS reference number uses a 2 byte (16 bit) value.
First SMS UDH value:
Second SMS UDH Value:
These UDH values are read as follows:
