GSM-7
GSM-7 is the 7-bit alphabet for basic Latin text in SMS: 160 characters per segment, or 70 once the message switches to UCS-2.
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GSM-7 is the 7-bit alphabet that SMS uses by default for Latin letters, digits and common symbols. Text inside it fits 160 characters in one segment; one character outside moves the whole message to UCS-2.
Encoding, units and segments
- Encoding
- GSM-7
- Characters
- 20
- Units
- 20
- Segments
- 1
Text description
The figure runs one sample message through the segment counter and shows four fields: encoding, character count, encoding units and segment count. Units are septets in GSM-7 and 16-bit code units in UCS-2.
Why the count matters
3GPP TS 23.038 defines the alphabet: basic Latin letters, digits, common punctuation, a few accented letters such as é, ü, ñ and ç, and symbols such as £. An escape character adds curly braces, square brackets and the euro sign, at two septets each. A concatenated GSM-7 segment holds about 153 septets, not 160.
One character outside the table moves the whole message to UCS-2, from 160 characters per segment to 70. Escaping can also split a 160-character message. Normalize punctuation and test the text in the SMS segment calculator.