Multi-part (concatenated) SMS
Concatenated SMS ensures that your entire message will be delivered, whether it takes one text message or three message parts – the end user will always receive your SMS as a single message.
Here’s how concatenated SMS works
Concatenated SMS splits up your message into smaller parts, which are sent as individual SMS messages and recombined on the recipient’s handset. This concatenation process requires additional information to be added to each concatenated text message for identifying and ordering each message part. This information is known as the user data header (UDH) and takes up 48 bits of each SMS payload, which means only 1072 bits are left over for the content of the message.