Unstructured Supplementary Service Data

From Wikipedia, the free encyclopedia

The external links in this article may not follow Wikipedia's content policies or guidelines.
Please improve this article by removing excessive or inappropriate external links.

USSD on a Sony Ericsson mobile phone

Unstructured Supplementary Service Data is a capability of all GSM phones. 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 Phase 1 specified in GSM 02.90 only support mobile initiated operation (pull operation). In the core network the message is delivered over MAP using MAP_PROCESS_UNSTRUCTURED_SS_DATA command.

USSD Phase 2 specified in GSM 03.90 support for network initiated operation (pull and push operation) so that in the MAP Phase 2 and 2+ specification 3 command is used for USSD i.e. MAP_PROCESS_UNSTRUCTURED_SS_REQUEST, MAP_UNSTRUCTURED_SS_REQUEST and MAP_UNSTRUCTURED_SS_NOTIFY command.

As an analogy, USSD is similar to telnet, while SMS is similar to mail..

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. The function that is triggered when sending USSD is network dependent and depends on what kind of services the operator has made available.

Example USSD codes: