What is UDH (User data header)?
User data header (UDH) is a binary structure that may be present at the start of a short message in an SMS. It does not contain text but defines how to process the message.
UDH is part of the SMS that tells the receiving handset type of message sent to ensure correct SMS delivery. It is commonly used for concatenated short messages.
What is the difference between User data header and Payload data?
The User data header contains data about how to process the message, and the Payload data is the actual message content the origin sends to a destination.