User Data Header

User Data Header (UDH) is a binary structure which may be present at the start of a short message in the Short Message Service in GSM. It does not contain any text, but it specifies how the message should be formatted and processed.

UDH can be used to form Concatenated SMS, to enrich the content of the message with colors, text formatting, small pictures and animations and simple music which are used in Enhanced Messaging Service (EMS), to convey port numbers which may cause start of an application in the mobile phone, which is used for Multimedia Messaging Service (MMS) or to indicate using of national language shift tables.