Unstructured Supplementary Service Data (USSD) is a protocol used by GSM cellular telephones to communicate with the service provider’s computers. USSD is part of the GSM standard (GSM 03.90) it supports mobile-initiated (“pull”) and network-initiated (“push”) operation as well. In the core network, the message is delivered over MAP. All GSM phones have USSD capability.
USSD is similar to SMS, however there are a few key differentiators:
- Session based – USSD messages create a real-time connection during a USSD session. The connection remains open, allowing a two-way exchange of a sequence of data. This makes USSD more responsive than services that use SMS.
- Real Time service – messages are delivered instantly and standard requires that messages will be delivered in less then 2 seconds.
- USSD is not store and forward
- Secured – data is not stored on mobile device
- Messages are up to 182 alphanumeric characters in length.
USSD is mainly used today for call back services while roaming; for customers support services such as, checking pre-paid balance and for mobile payments. VascoDe patent pending technology leverages USSD in order to provide advanced applications on all mobile devices in real time.
