Introduction

Unstructured Supplementary Service Data ("USSD") is a feature offered by GSM network. It allows data communication with the Network Operator ("CELCO") in wireless mode. It is generally associated with real-time or instant messaging type phone services. There is no store-and-forward capability that is typical of 'normal' short messages (in other words, an SMSC is not present in the processing path). Response times for interactive USSD based services are generally quicker than those used for SMS.

USSD is typically used as a 'trigger' to invoke independent calling services which don't require the overhead and additional usage costs of an SMSC, such as a callback service (e.g. cheaper phone charges while roaming), or interactive menuing service (e.g. stock quotes, sporting results).

USSD is a standard for transmitting information over GSM signalling channels. It is mostly used as a method to query the available balance and other similar information in pre-paid GSM services.

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

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.

In SMS API version 5 you are able to send USSD command to the CELCO, and obtain a response. Before you can use the USSD method, please refer to your IDE guide on setting up the USSD class.

1. Check Credit Balance - check the credit balance of prepaid account (Hotlink, Xpax, Digi Prepaid) without the need of removing the SIM card from modem.

2. Reload Account - to reload or top-up prepaid account without the need of removing the SIM card from modem.