USSD – Unstructured Supplementary Service Data Flow
USSD – Unstructured Supplementary Service Data Flow
USSD is an acronym of Unstructured Supplementary Service Data. We are normally use the code *123# to check our balance in mobile. The code starting with * and ending with # symbol is called MMI Code. MMI – Man Machine Interface. Also we use this format to topup our mobile balance using voucher pin. Here we going to see details about USSD Flows and Functions.
Different types of MMI Codes are there.
- SS Codes
- USSD Codes
- Manufacturer defined MMI codes
- SIM Control Codes
1. SS Codes – Supplementary Service Codes
These codes are hard coded into every GSM/UMTS/LTE device worldwide and cannot be changed by your network operator.
For example, These codes are used to control Call Forwarding Features – *21*12345678# (and press <SEND> or Call Button). You are now instructing your calls to be forwarded to the number 12345678.
2. USSD Code
If you enter a code that at least ends in a hash sign (and press <SEND>) and is not recognized by the phones MMI parser, the code will be sent to the network. It then depends on the network if this code is supported .
Note: For SS and USSD codes you always need to press the <SEND> key after entering them, so it is not possible to automatically execute those codes with a tel-URL.
- To check the balance using short code *123#
- To topup our mobile using voucher pin *139*12345678# (12345678 is a voucher pin)
- To activate Bundle/Booster pack services *144*5544# (5544 is a bundle pack or booster pack code)
- To activate or deactivate other services
3. Manufacturer defined MMI codes
Codes specific to your phone model that have been built in by the manufacturer, for example, To activate service menus or reset the device. These codes also contain * and # characters. Since the codes are not being sent to the network, you don’t have to press the <SEND> key at the end – they are executed as soon as the last digit or character has been entered.
There is one code that is mandatory for all manufacturers of GSM/UMTS/LTE phones to implement:*#06#
It shows the devices IMEI (Internatiol Mobile Equipment Identifier)
4. SIM Control Codes
These codes are used, for example, to change your SIMs PIN code.
**04*1234*6789*6789# would change your PIN code from “1234” to “6789”.
These codes are also executed without pressing the <SEND> key.
Reference : https://berlin.ccc.de/~tobias/mmi-ussd-ss-codes-explained.html
The complete specification for the MMI interface of GSM/UMTS/LTE devices can be found in 3GPP TS 22.030: “Man-Machine Interface (MMI) of the User Equipment (UE)”