The Unstructured Supplementary Service Data (USSD) mechanism enables a Mobile Station (MS) and Public Land Mobile Network (PLMN) operator defined application servers to communicate.

This document defines the requirements for handling USSD at the MS and network entities. It does not include specification of particular applications, nor does it specify how a particular application is selected.

This document also defines architecture requirements (stage 2) and the protocol details (stage 3) of the USSD.