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.
[2] Presence of User Data Header is indicated by the TP-UDHI (Transfer Layer Protocol User Data Header Indicator) bit - 6th bit of the first octet of the GSM 03.40 or 3GPP 23.040 message.
The longer the UDH, the less space remains for the message text or other contents.
The next table shows how a TP-UD of a message in the GSM 7 bit default alphabet containing text 'Hi' with a predefined sound 'Chord high' will be encoded: The total message length TP-UDL will be 8.
The UDH is used in other protocols for short message transport - Short Message Peer-to-Peer (SMPP), Universal Computer Protocol (UCP) and in WEMT teleservice in CDMA2000.