User Data Header (UDH) is a binary structure which may be present at the start of a short message in the

Short Message Service Short Message/Messaging Service, commonly abbreviated as SMS, is a text messaging service component of most telephone, Internet and mobile device systems. It uses standardized communication protocols that let mobile devices exchange short tex ...

GSM The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such ...

. 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 In the cellular phone industry, mobile phones and their networks sometimes support concatenated short message service (or concatenated SMS) to overcome the limitation on the number of characters that can be sent in a single SMS text message transmi ...

, 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 Enhanced Messaging Service (EMS) was a cross-industry collaboration between Samsung, Ericsson, Motorola, Siemens and Alcatel among others, which provided an application-level extension to Short Message Service (SMS) for cellular phones available on ...

(EMS), to convey port numbers which may cause start of an application in the mobile phone, which is used for

Multimedia Messaging Service Multimedia Messaging Service (MMS) is a standard way to send messages that include multimedia content to and from a mobile phone over a cellular network. Users and providers may refer to such a message as a PXT, a picture message, or a multimedia ...

(MMS) or to indicate using of national language shift tables. UDH is defined in 3GPP 23.040 (originally GSM 03.40).3rd Generation Partnership Project; Technical realization of the Short Message Service (SMS)
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Technical Realization

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. If UDH is present, it is at the beginning of the TP-UD (TP-User Data) field and it always starts with an UDHL (UDH Length) octet. The rest of UDH is a sequence of Tag-Length-Value triplets. The Tag is named Information-Element-Identifier (IEI) and is always 1 octet long, the Length octet is always 1 octet long and it specifies the length of the Information Element Data. UDH uses space intended for the message payload. The longer the UDH, the less space remains for the message text or other contents. When TP-UD contains seven-bit data, the length of TP-UD is given in septets (but UDHL is still in octets, so length in septets is (UDHL + 1) * 8 / 7) and the UDH is filled to a septet boundary with 0-6 zero bits. 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. (UDH has 8 * (1 + 4) = 40 bits, 2 bits is the padding as (40 + 2) / 7 = 6 without remainder, 2 * 7 = 14 bits for text; total TP-UD length is 40 + 2 + 14 = 56 bits = 7 octets = 8 septets.)

UDH Information Elements

{, class="wikitable" , - ! IEI (hex) !! Meaning !! Classification !! Length !! May repeat , - , 00 , , Concatenated short messages, 8-bit reference number , , SMS Control , , 3 , , no , - , 01 , , Special SMS Message Indication , , SMS Control , , 2 , , yes , - , 02 , , Reserved , , N/A , , N/A , , yes , - , 03 , , Not used to avoid misinterpretation as character, , N/A , , N/A , , yes , - , 04 , , Application port addressing scheme, 8 bit address , , SMS Control , , 2 , , no , - , 05 , , Application port addressing scheme, 16 bit address , , SMS Control , , 4 , , no , - , 06 , , SMSC Control Parameters , , SMS Control , , 1 , , no , - , 07 , , UDH Source Indicator , , SMS Control , , 1 , , yes , - , 08 , , Concatenated short message, 16-bit reference number , , SMS Control , , 4 , , no , - , 09 , , Wireless Control Message Protocol , , SMS Control , , 1-255 , , yes , - , 0A , , Text Formatting , , EMS Control , , 3-4 , , yes , - , 0B , , Predefined Sound , , EMS Content , , 2 , , yes , - , 0C , , User Defined Sound ( iMelody max 128 bytes) , , EMS Content , , 2-129 , , yes , - , 0D , , Predefined Animation , , EMS Content , , 2 , , yes , - , 0E , , Large Animation (16*16 times 4 = 32*4 =128 bytes), , EMS Content , , 129 , , yes , - , 0F , , Small Animation (8*8 times 4 = 8*4 =32 bytes) , , EMS Content , , 33 , , yes , - , 10 , , Large Picture (32*32 = 128 bytes) , , EMS Content , , 129 , , yes , - , 11 , , Small Picture (16*16 = 32 bytes) , , EMS Content , , 33 , , yes , - , 12 , , Variable Picture , , EMS Content , , 4-255 , , yes , - , 13 , , User prompt indicator , , EMS Control , , 1 , , yes , - , 14 , , Extended Object , , EMS Content , , 7-255 , , yes , - , 15 , , Reused Extended Object , , EMS Control , , 3 , , yes , - , 16 , , Compression Control , , EMS Control , , 3-255 , , no , - , 17 , , Object Distribution Indicator , , EMS Control , , 2 , , yes , - , 18 , , Standard WVG object , , EMS Content , , 1-255 , , yes , - , 19 , , Character Size WVG object , , EMS Content , , 1-255 , , yes , - , 1A , , Extended Object Data Request Command , , EMS Control , , 0-255 , , no , - , 1B , , Reserved for future EMS features , , N/A , , 0-255 , , yes , - , 1C , , Reserved for future EMS features , , N/A , , 0-255 , , yes , - , 1D , , Reserved for future EMS features , , N/A , , 0-255 , , yes , - , 1E , , Reserved for future EMS features , , N/A , , 0-255 , , yes , - , 1F , , Reserved for future EMS features , , N/A , , 0-255 , , yes , - , 20 , , RFC 822 E-Mail Header , , SMS Control , , 1 , , no , - , 21 , , Hyperlink format element , , SMS Control , , 0-255 , , yes , - , 22 , , Reply Address Element , , SMS Control , , 1-255 , , no , - , 23 , , Enhanced Voice Mail Information , , SMS Control , , 0-255 , , no , - , 24 , , National Language Single Shift , , SMS Control , , 1 , , no , - , 25 , , National Language Locking Shift , , SMS Control , , 1 , , no , - , 26 – 6F , , Reserved for future use , , N/A , , 0-255 , , N/A , - , 70 – 7F , , (U)SIM Toolkit Security Headers , , SMS Control , , 0-255 , , ? , - , 80 – 9F , , SME to SME specific use , , SMS Control , , 0-255 , , ? , - , A0 – BF , , Reserved for future use , , N/A , , 0-255 , , ? , - , C0 – DF , , SC specific use , , SMS Control , , 0-255 , , ? , - , E0 – FF , , Reserved for future use , , N/A , , 0-255 , , ?

Use in Other Protocols

The UDH is used in other protocols for short message transport -

Short Message Peer-to-Peer Short Message Peer-to-Peer (SMPP) in the telecommunications industry is an open, industry standard protocol designed to provide a flexible data communication interface for the transfer of short message data between External Short Messaging Entit ...

(SMPP), Universal Computer Protocol (UCP) and in WEMT teleservice in

CDMA2000 CDMA2000 (also known as C2K or IMT Multi‑Carrier (IMT‑MC)) is a family of 3G mobile technology standards for sending voice, data, and Signaling (telecommunication), signaling data between mobile phones and cell sites. It is developed by 3GP ...

References

GSM standard

Technical Realization

UDH Information Elements

Use in Other Protocols

See also

References