Each segment is sent as a separate SMS message and then reassembled by the recipient's mobile device to display as a single, cohesive message. This technology is essential for providing a seamless user experience when sending text messages that exceed the standard SMS character limit.
When a user sends a text message that exceeds the standard SMS character limit, the message is automatically split into smaller segments. Each segment adheres to the character limit for a single SMS (160 characters for GSM-7, 70 characters for Unicode).
Each segment contains a UDH, a special header added to the message data. The UDH includes information necessary for reassembling the segments. The UDH typically contains the total number of segments, the sequence number of the current segment, and a unique identifier for the entire concatenated message.
Each segment, including its UDH, is sent as an individual SMS message. The mobile network processes and delivers each segment separately. Once all segments are received, the device combines them to display as a single, coherent message.
