Unstructured Supplementary Services Data

Introduction

Unstructured Supplementary Service Data (USSD) is a technology unique to GSM. It is a capability built into the GSM standard for support of transmitting information over the signaling channels of the GSM network. USSD provides session-based communication, enabling a variety of applications.

Technology

USSD is defined within the GSM standard in the documents GSM 02.90 (USSD Stage 1) and GSM 03.90 (USSD Stage 2).

Key attributes:

USSD is instead session oriented, unlike SMS, which is a store-and-forward, transaction-oriented technology.

Turnaround response times for interactive applications are shorter for USSD than SMS because of the session-based feature of USSD, and because it is NOT a store and forward service.

Users do not need to access any particular phone menu to access services with USSD- they can enter the Unstructured Supplementary Services Data (USSD) command direct from the initial mobile phone screen.

USSD commands are routed back to the home mobile network’s Home Location Register (HLR), allowing for the virtual home environment concept – the ability for services (based on USSD in this case) to work just as well and in exactly the same way when users are roaming.

Unstructured Supplementary Services Data (USSD) works on all existing GSM mobile phones.

Both SIM Application Toolkit and the Wireless Application Protocol support USSD.

USSD in Operation

In operation, USSD is used to send text between the user and some application. USSD should be thought of as a trigger rather than an application itself. However, it enables other applications such as prepaid. In operation, it is not possible to bill for USSD directly, but instead bill for the application associated with the use of USSD such as circuit switch data, SMS, or prepaid.