More Information

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.

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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.

Benefits of USSD

The primary benefit of USSD is that it allows for very fast communication between the user and an application. Most of the applications enabled by USSD are menu based and include services such as mobile prepay and chat.

USSD Enabled Applications

Prepaid Roaming

USSD is used an excellent technology to enable roaming with mobile prepay service. Platform providers such as SICAP offer solutions that involve the use of USSD.

The mobile prepay uses a menu and a USSD connection to indicate the desire to initiate a call while roaming. The MSC connects through to the HLR in the home network (via the SS7 network). The HLR routes the request to the USSD gateway, which in turn routes the request to the prepay application server. The application server checks the balance and provides a call handling instructions response back through the same path to the serving MSC in the visited network. Additionally, a message is sent from a SMSC to the prepay customer, indicating the amount of airtime available on the account.

Chat

Mobile chatting and friend finder applications are another perfect use for USSD as a menu driven application enabling other applications. USSD is the front-end to these types of applications, which require a menu and fast connections for the user interface.

It is important to note that friend finder applications require location determination/management and presence/availability technologies and applications to allow the closed user group to detect if, when, and where members are available. See the Location Based Services paper for more information.

Additional Resources:

Books about: WAP