the SMPP operation (or command). If the most significant bit is cleared, this is a request operation. Otherwise it is a response. command_status Always has a value of 0 in requests; in responses it carries information about the result of the operation sequence_number Is used to correlate requests and responses within an SMPP session; allows asynchronous communication (using a sliding window method) All numeric fields in SMPP use the big endian order, which means that the first octet is the Most Significant Byte (MSB). Example This is an example of the binary encoding of a 60-octet submit_sm PDU. The data is shown in Hex octet values as a single dump and followed by a header and body break-down of that PDU. This is best compared with the definition of the submit_sm PDU from the SMPP specification in order to understand how the encoding matches the field by field definition. The value break-downs are shown with decimal in parentheses and Hex values after that. Where you see one or several hex octets appended, this is because the given field size uses 1 or more octets encoding. Again, reading the definition of the submit_sm PDU from the spec will make all this clearer. PDU header 'command_length', (60) ... 00 00 00 3C 'command_id', (4) ... 00 00 00 04 'command_status', (0) ... 00 00 00 00 'sequence_number', (5) ... 00 00 00 05 PDU body 'service_type', () ... 00 'source_addr_ton', (2) ... 02 'source_addr_npi', (8) ... 08 'source_addr', (555) ... 35 35 35 00 'dest_addr_ton', (1) ... 01 'dest_addr_npi', (1) ... 01 'dest_addr', (555555555) ... 35 35 35 35 35 35 35 35 35 00 'esm_class', (0) ... 00 'protocol_id', (0) ... 00 'priority_flag', (0) ... 00 'schedule_delivery_time', (0) ... 00 'validity_period', (0) ... 00 'registered_delivery', (0) ... 00 'replace_if_present_flag', (0) ... 00 'data_coding', (3) ... 03 'sm_default_msg_id', (0) ... 00 'sm_length', (15) ... 0F 'short_message', (Hello Wikipedia) ... 48 65 6C 6C 6F 20 57 69 6B 69 70 65 64 69 61 Note that the text in the short_message field must match the data_coding. When the data_coding is 8 (UCS2), the text must be in UCS-2BE (or its extension, UTF-16BE). When the data_coding indicates a 7-bit encoding, each septet is stored in a separate octet in the short_message field (with the most significant bit set to 0). SMPP 3.3 data_coding exactly copied TP-DCS values of GSM 03.38, which make it