Concatenated SMS sending
According to the SMPP protocol specification, the maximum length of one SMS to be sent is:
for messages in Latin: 160 characters;
for messages in Cyrillic: 70 characters.
SMS exceeding the maximum length are called multipart or concatenated SMS and are usually split into parts when sent. The length of one part is:
for messages in Latin: 153 characters;
for messages in Cyrillic: 67 characters.
To send concatenated SMS, one of the following three technologies is employed:
UDH (user data header) is a special header at the beginning of the text of the SMS;
SAR is analogue of the UDH header; due to the location in TLV fields, it will not reduce the size of one part of an SMS
message_payload is TLV field hosting the entire message content
Detailed information about the above technologies can be found in the SMPP protocol specification.
⚠️IMPORTANT:
In each part of a multipart SMS, the values of the following fields must match:
service_type;
source_addr_ton;
source_addr_npi;
source_addr;
dest_addr_ton;
dest_addr_npi;
destination_addr;
esm_class;
protocol_id;
priority_flag;
validity_period;
registered_delivery;
data_coding.
A message cannot be delivered until all of its parts have been received.
The wait time for all parts of a concatenated message is 10 minutes. If all parts are not received after this period, the message will not be sent.
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