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User Data Header
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<h2 id="technical-realization">Technical Realization</h2> <p>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 <a href="/facts/GSM_03.40/9AqlJ2DP">GSM 03.40 or 3GPP 23.040</a> message. </p><p>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 field is always 1 octet long and it specifies the length of the Information Element Data. </p><p>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: </p> <table><tbody><tr><th>TP-UD Octet</th><th>1</th><th>2</th><th>3</th><th>4</th><th>5</th><th>6</th><th>7</th></tr><tr><td>Value (hex)</td><td>04</td><td>0B</td><td>02</td><td>00</td><td>08</td><td>20</td><td>D3</td></tr><tr><td>Meaning</td><td>UDH Length</td><td>IEI: Predefined sound</td><td>IE Length</td><td>Position</td><td>Chord high</td><td>6 lower bits of the 1st char + 2 fill bits</td><td>7 lower bits of the 2nd char + 1 upper bit of the first char</td></tr></tbody></table> <p>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.) </p> <h2 id="udh-information-elements">UDH Information Elements</h2> <table><tbody><tr><th>IEI (hex)</th><th>Meaning</th><th>Classification</th><th>Length</th><th>May repeat</th></tr><tr><td>00</td><td><a href="/facts/Concatenated_SMS/z80CoB3z">Concatenated short messages</a>, 8-bit reference number</td><td>SMS Control</td><td>3</td><td>no</td></tr><tr><td>01</td><td>Special SMS Message Indication</td><td>SMS Control</td><td>2</td><td>yes</td></tr><tr><td>02</td><td>Reserved</td><td>N/A</td><td>N/A</td><td>yes</td></tr><tr><td>03</td><td>Not used to avoid misinterpretation as <LF> character</td><td>N/A</td><td>N/A</td><td>yes</td></tr><tr><td>04</td><td><a href="/facts/Smart_Messaging/x35kUgKQ">Application port addressing scheme</a>, 8 bit address</td><td>SMS Control</td><td>2</td><td>no</td></tr><tr><td>05</td><td><a href="/facts/Smart_Messaging/x35kUgKQ">Application port addressing scheme</a>, 16 bit address</td><td>SMS Control</td><td>4</td><td>no</td></tr><tr><td>06</td><td>SMSC Control Parameters</td><td>SMS Control</td><td>1</td><td>no</td></tr><tr><td>07</td><td>UDH Source Indicator</td><td>SMS Control</td><td>1</td><td>yes</td></tr><tr><td>08</td><td><a href="/facts/Concatenated_SMS/z80CoB3z">Concatenated short message</a>, 16-bit reference number</td><td>SMS Control</td><td>4</td><td>no</td></tr><tr><td>09</td><td><a href="/facts/Wireless_Application_Protocol/UxhCWfnv">Wireless Control Message Protocol</a></td><td>SMS Control</td><td>1-255</td><td>yes</td></tr><tr><td>0A</td><td>Text Formatting</td><td>EMS Control</td><td>3-4</td><td>yes</td></tr><tr><td>0B</td><td>Predefined Sound</td><td>EMS Content</td><td>2</td><td>yes</td></tr><tr><td>0C</td><td>User Defined Sound (<a href="/facts/IMelody/Hzsn9Nxj">iMelody</a> max 128 bytes)</td><td>EMS Content</td><td>2-129</td><td>yes</td></tr><tr><td>0D</td><td>Predefined Animation</td><td>EMS Content</td><td>2</td><td>yes</td></tr><tr><td>0E</td><td>Large Animation (16*16 times 4 = 32*4 =128 bytes)</td><td>EMS Content</td><td>129</td><td>yes</td></tr><tr><td>0F</td><td>Small Animation (8*8 times 4 = 8*4 =32 bytes)</td><td>EMS Content</td><td>33</td><td>yes</td></tr><tr><td>10</td><td>Large Picture (32*32 = 128 bytes)</td><td>EMS Content</td><td>129</td><td>yes</td></tr><tr><td>11</td><td>Small Picture (16*16 = 32 bytes)</td><td>EMS Content</td><td>33</td><td>yes</td></tr><tr><td>12</td><td>Variable Picture</td><td>EMS Content</td><td>4-255</td><td>yes</td></tr><tr><td>13</td><td>User prompt indicator</td><td>EMS Control</td><td>1</td><td>yes</td></tr><tr><td>14</td><td>Extended Object</td><td>EMS Content</td><td>7-255</td><td>yes</td></tr><tr><td>15</td><td>Reused Extended Object</td><td>EMS Control</td><td>3</td><td>yes</td></tr><tr><td>16</td><td>Compression Control</td><td>EMS Control</td><td>3-255</td><td>no</td></tr><tr><td>17</td><td>Object Distribution Indicator</td><td>EMS Control</td><td>2</td><td>yes</td></tr><tr><td>18</td><td>Standard WVG object</td><td>EMS Content</td><td>1-255</td><td>yes</td></tr><tr><td>19</td><td>Character Size WVG object</td><td>EMS Content</td><td>1-255</td><td>yes</td></tr><tr><td>1A</td><td>Extended Object Data Request Command</td><td>EMS Control</td><td>0-255</td><td>no</td></tr><tr><td>1B</td><td>Reserved for future EMS features</td><td>N/A</td><td>0-255</td><td>yes</td></tr><tr><td>1C</td><td>Reserved for future EMS features</td><td>N/A</td><td>0-255</td><td>yes</td></tr><tr><td>1D</td><td>Reserved for future EMS features</td><td>N/A</td><td>0-255</td><td>yes</td></tr><tr><td>1E</td><td>Reserved for future EMS features</td><td>N/A</td><td>0-255</td><td>yes</td></tr><tr><td>1F</td><td>Reserved for future EMS features</td><td>N/A</td><td>0-255</td><td>yes</td></tr><tr><td>20</td><td>RFC 822 E-Mail Header</td><td>SMS Control</td><td>1</td><td>no</td></tr><tr><td>21</td><td>Hyperlink format element</td><td>SMS Control</td><td>0-255</td><td>yes</td></tr><tr><td>22</td><td>Reply Address Element</td><td>SMS Control</td><td>1-255</td><td>no</td></tr><tr><td>23</td><td>Enhanced Voice Mail Information</td><td>SMS Control</td><td>0-255</td><td>no</td></tr><tr><td>24</td><td>National Language Single Shift</td><td>SMS Control</td><td>1</td><td>no</td></tr><tr><td>25</td><td>National Language Locking Shift</td><td>SMS Control</td><td>1</td><td>no</td></tr><tr><td>26</td><td>Filler</td><td>SMS Control</td><td>0-255</td><td>yes</td></tr><tr><td>27 – 6F</td><td>Reserved for future use</td><td>N/A</td><td>0-255</td><td>N/A</td></tr><tr><td>70 – 7F</td><td>(U)SIM Toolkit Security Headers</td><td>SMS Control</td><td>0-255</td><td>?</td></tr><tr><td>80 – 9F</td><td>SME to SME specific use</td><td>SMS Control</td><td>0-255</td><td>?</td></tr><tr><td>A0 – BF</td><td>Reserved for future use</td><td>N/A</td><td>0-255</td><td>?</td></tr><tr><td>C0 – DF</td><td>SC specific use</td><td>SMS Control</td><td>0-255</td><td>?</td></tr><tr><td>E0 – FF</td><td>Reserved for future use</td><td>N/A</td><td>0-255</td><td>?</td></tr></tbody></table> <h2 id="use-in-other-protocols">Use in Other Protocols</h2> <p>The UDH is used in other protocols for short message transport - <a href="/facts/Short_Message_Peer-to-Peer/T6QnR9Qr">Short Message Peer-to-Peer</a> (SMPP), <a href="/facts/Universal_Computer_Protocol/vSTlEK5y">Universal Computer Protocol</a> (UCP) and in WEMT <a href="/facts/Teleservice/986Loqdu">teleservice</a> in <a href="/facts/CDMA2000/yF4B3rfl">CDMA2000</a>. </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Short_Message_Service/kacRfW0X">Short Message Service</a></li> <li><a href="/facts/GSM_03.38/eFjyKNVp">GSM 03.38</a></li> <li><a href="/facts/Enhanced_Messaging_Service/hzdWGdnv">Enhanced Messaging Service</a></li> <li><a href="/facts/Multimedia_Messaging_Service/Pg5CvwLx">Multimedia Messaging Service</a></li> <li><a href="/facts/Short_Message_Peer-to-Peer/T6QnR9Qr">Short Message Peer-to-Peer</a></li> <li><a href="/facts/Universal_Computer_Protocol/vSTlEK5y">Universal Computer Protocol</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"Alphabets and language-specific information". portal.3gpp.org. Retrieved 2021-07-19. <a href="https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=745" target="_blank">https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=745</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>3rd Generation Partnership Project; Technical realization of the Short Message Service (SMS) <a href="http://www.3gpp.org/ftp/Specs/html-info/23040.htm" target="_blank">http://www.3gpp.org/ftp/Specs/html-info/23040.htm</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> </ol>