How do I send concatenated messages via SMPP?


Sending concatenated messages via SMPP.

Applies To

  • SMPP
  • SMS
  • Concatenated Messages


  1. On SMPP:submit_sm the UDHI (User Data Header Indicator) in the esm_class parameter: esm_class = 0x40 x1xxxxxx is set in the esm_class field to indicate UDHI is true.
  2. The concatenation UDH values are inserted at the start of the message body.


Message 1 (UDH+153 chars length message)

esm_class = 0x40 x1xxxxxx

short_message = 0x05 0x00 0x03 0x05 0x02 0x01 Barcelona are to appeal against Uefa's proposal to ban Andres Iniesta for an additional Champions League match for allegedly provoking a yellow card. The

Message 2 (UDH+rest of the message)

esm_class = 0x40 x1xxxxxx

short_message = 0x05 0x00 0x03 0x05 0x02 0x02  26-year-old Spain midfielder was booked in the quarter-final against Shakhtar Donetsk, meaning he missed the return leg but would then be available.

Concatenation UDH Structure

Byte Description
05 Length of UDH (5 bytes)
00 Indicator for concatenated message
03 Subheader length (3 bytes)
XX Message identification - Can be any hexadecimal
number, but needs to match the UDH Reference Number of all concatenated SMS
YY Number of pieces of the concatenated message
ZZ Sequence number (used by the mobile to concatenate the split messages)

Maximum Characters Per Concatenated Message

The maximum number of characters per concatenated message depends on the encoding.

  • 153 characters for 7-bit encoding (e.g., Latin-1/9 and GSM8)
  • 134 characters for 8-bit encoding (Binary)
  • 67 characters for 16-bit encoding (Unicode)
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