We have seen how you can use the User Data Header (UDH) in an SMS message to combine several SMS messages into one bigger one. Here is another application of the UDH:
Text formatting in SMS
Remember that the UDH consists of Information Elements (IE) that each has the following structure
| Length | Value | Description |
| 1 octet | IEI | Information Element Identifier. This determines what this IE is about. |
| 1 octet | IE length | The length of the data belonging to this IE in octets. |
| n octets | IE data | The meaning of the content varies per IEI. |
The text formatting is controlled by just one IE. Here is a description:
| Length | Value | Description |
| 1 octet | IEI = 0x0A | IEI 0x0A is used to describe text formatting. |
| 1 octet | IE length = 0×04 | The length of the data is 0×03 or 0×04 depending on whether the color octet(below) is used. |
| 1 octet | start position | The formatting described in the formatting octet (below) applies to start the character at the position indicated here. |
| 1 octet | length | The formatting applies to the number of characters indicated by this octet. The value 0 means that the formatting is the new default formatting. |
| 1 octet | formatting | This octet indicates:
|
| 1 octet | color | This octet is optional, its presence is through the IE length octet. This octet controls both background and foreground colors. |
Now the only thing that is left to describe the formatting and color octets is more detail:
The formatting octet’s 8 bits have the following meaning:
| Bits | Value | Meaning |
| 1 and 0 (right most bits) |
0 = 0×00 1 = 0×01 2 = 0×02 3 = 0×03 |
Left aligned Center aligned Right aligned Default |
| 3 and 2 | 0 = 0×00 1 = 0×04 2 = 0×08 3 = 0x0C |
Normal size Large text Small text Unused |
| 4 | 0 = 0×00 1 = 0×10 |
Bold off Bold on |
| 5 | 0 = 0×00 1 = 0×20 |
Italic off Italic on |
| 6 | 0 = 0×00 1 = 0×40 |
Underline off Underline on |
| 7 | 0 = 0×00 1= 0×80 |
Strikethrough off Strikethrough on |
The values can be combined using the bitwise OR. For instance, a formatting octet with value 0×39 would mean center-aligned, small text, bold and italic.
The color octet consists of 2 4 bit values:
| Bits | Value | Meaning |
| 3-0 (right most bits) | 0 = 0×00 1 = 0×01 2 = 0×02 3 = 0×03 4 = 0×04 5 = 0×05 6 = 0×06 7 = 0×07 8 = 0×08 9 = 0×09 10 = 0x0A 11 = 0x0B 12 = 0x0C 13 = 0x0D 14 = 0x0E 15 = 0x0F |
Text black Text dark grey Text dark red Text dark yellow Text dark green Text dark cyan Text dark blue Text dark magenta Text grey Text white Text bright red Text bright yellow Text bright green Text bright cyan Text bright blue Text bright magenta |
| 7-4 (left most bits) | 0 = 0×00 1 = 0×10 2 = 0×20 3 = 0×30 4 = 0×40 5 = 0×50 6 = 0×60 7 = 0×70 8 = 0×80 9 = 0×90 10 = 0xA0 11 = 0xB0 12 = 0xC0 13 = 0xD0 14 = 0xE0 15 = 0xF0 |
Background black Background dark grey Background dark red Background dark yellow Background dark green Background dark cyan Background dark blue background dark magenta Background grey Background white Background bright red Background bright yellow Background bright green Background bright cyan Background bright blue background bright magenta |
Again you can use a bitwise OR to combine any text and background color.
Now for a complete walkthrough of an example SMS with some text formatting. Here is the AT command to send the message:
AT+CMGS=100 0041000B915121551532F40000631A0A031906200A032104100A032705040A032E05080A0438 07002B8ACD29A85D9ECFC3E7F21C340EBB41E3B79B1E4EBB41697A989D1EB340E2379BCC02B1 C3F27399059AB7C36C3628EC2683C66FF65B5E2683E8653C1D
Here is the detailed analysis to help you understand it:
| Size | Value | Description |
| 1 octet | 0×00 | We don’t supply a SMSC number. |
| 1 octet | 0×41 | PDU type and options. This is a plain SUBMIT-PDU and there is a UDH present. |
| 1 octet | 0×02 | Our message reference. |
| 1 octet | 0x0B | Size of destination telephone number (in digits) |
| 1 octet | 0×91 | International numbering plan. |
| 6 octets | 0x5121551532f4 | This represents the destination and it translates to 1 512 555 1234 |
| 1 octet | 0×00 | Protocol identifier. |
| 1 octet | 0×00 | Data Coding Scheme. DCS 0×00 stands for a plain GSM-7 encoded text message. |
| 1 octet | 0×63 | User Data Length or payload size (in septets). |
| 1 octet | 0x1A | User Data Header Length or UDHL. Size of the UDH in octets. |
| 1 octet | 0x0A | Start of a text formatting IEI. |
| 1 octet | 0×03 | IE length is 3 octets |
| 1 octet | 0×19 | Start formatting at the 25th character |
| 1 octet | 0×06 | Formatting is for 6 characters |
| 1 octet | 0×20 | Use italic text |
| 1 octet | 0x0A | Start of a text formatting IEI. |
| 1 octet | 0×03 | IE length is 3 octets |
| 1 octet | 0×21 | Start formatting at the 33rd character |
| 1 octet | 0×04 | Formatting is for 4 characters |
| 1 octet | 0×10 | Use bold text |
| 1 octet | 0x0A | Start of a text formatting IEI. |
| 1 octet | 0×03 | IE length is 3 octets |
| 1 octet | 0×27 | Start formatting at the 39th character |
| 1 octet | 0×05 | Formatting is for 5 characters |
| 1 octet | 0×04 | Use large text |
| 1 octet | 0x0A | Start of a text formatting IEI. |
| 1 octet | 0×03 | IE length is 3 octets |
| 1 octet | 0x2E | Start formatting at the 46th character |
| 1 octet | 0×05 | Formatting is for 5 characters |
| 1 octet | 0×08 | Use small text |
| 1 octet | 0x0A | Start of a text formatting IEI. |
| 1 octet | 0×04 | IE length is 4 octets |
| 1 octet | 0×38 | Start formatting at the 56th character |
| 1 octet | 0×07 | Formatting is for 5 characters |
| 1 octet | 0×00 | No text formatting |
| 1 octet | 0x2B | Background dark red and text bright yellow |
| 54 octets | The remainder of the octets contain the text:“EMS messages can contain italic, bold, large, small and colored text” |
The text produced by the messages (when received on a phone that supports all EMS features used) would look like this:
EMS messages can contain italic, bold, large, small and colored text
A phone that doesn’t support some or all of the EMS features used will simply skip over the IEs it doesn’t know and produce the text without the indicated markup
