How Text.lk Encodes Your Messages? UTF-16, GSM-7, GSM-7 Extension

Here is a simple explanation of GSM-7, GSM-7 Extension, and UTF-16 encoding as used on text.lk, written for easy understanding by all users:

---

GSM-7, GSM-7 Extension, and UTF-16 Encoding on text.lk

1. GSM-7 Character Encoding (GSM_7BIT)

GSM-7 is the main character set used for sending SMS messages on mobile networks. It includes the most common letters, numbers, and symbols used in many Western languages.

• How it works: Each character is stored using 7 bits (less than a full byte), which allows up to 160 characters in one SMS message.
• What it includes: Basic Latin letters (A-Z, a-z), digits (0-9), and common punctuation marks.
• Limitations: It does not support all characters from other languages or special symbols.
• Special characters: Some symbols like {, }, |, ^, € need an extra code, so they take up two character spaces in the message.
• Why use it: It’s efficient and lets you send more characters per SMS if you only use supported characters124.

Learn More about GSM-7 Character Encoding (GSM_7BIT)

2. GSM-7 Extension Table (GSM_7BIT_EX)

The GSM-7 Extension is a small extra set of characters not included in the main GSM-7 alphabet.

• How it works: These extra characters are sent using an escape code followed by the character code.
• Examples: Characters like €, ^, {, }, \, [, ], ~, and |.
• Impact: Each extended character counts as two characters in your SMS, reducing the total number of characters you can send in one message.
• When it matters: If your message includes any of these extended characters, it will use more space and might cost more14.

Learn More about GSM-7 Extension Table (GSM_7BIT_EX)

3. UTF-16 Character Encoding

UTF-16 is a different way to encode text that can represent every character in the world, including emojis, non-Latin scripts, and special symbols.

• How it works: Most common characters use 2 bytes (16 bits). Characters like emojis or historic scripts use 4 bytes (two 16-bit units).
• When it’s used: If your SMS contains any character not supported by GSM-7 or its extension (like emojis or Asian characters), the message is sent using UTF-16.
• Effect on SMS length: Because each character uses 2 bytes, the maximum number of characters per SMS drops to 70 (or 67 if the message is split into parts).
• Why it matters: Messages with UTF-16 encoding cost more because they use more space and fewer characters fit in one SMS45.

Learn More about UTF-16 Character Encoding

---

Summary for text.lk Users

• Use GSM-7 characters for longer SMS messages and lower costs.
• If you use special symbols from the GSM-7 Extension, your message length decreases slightly.
• If you include emojis or non-Latin characters, your message switches to UTF-16, which halves the number of characters per SMS and may increase cost.
• Always check your message content to know which encoding will be used and how many characters you can send in one SMS.

---

This simple guide helps you understand how text.lk handles SMS character encoding to optimize message length and cost.

Check sources

1. https://supportcenter.everbridge.com/hc/en-us/articles/19141701423771-EBS-GSM-7-and-UCS-2-Character-Encodings-and-Their-Importance-When-Sending-SMS-Messages
2. https://en.wikipedia.org/wiki/GSM_03.38
3. https://www.infobip.com/docs/sms/language
4. https://help.aninja.com/knowledge-base/sms-encoding-gsm-7-and-ucs-2/
5. https://thesmsworks.co.uk/blog/gsm-character-set/
6. https://help.goacoustic.com/hc/en-us/articles/360043843154–How-character-encoding-affects-SMS-message-length
7. https://support.dotdigital.com/en/articles/8199189-gsm-character-set