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

Figure 1 shows the architecture for handling of USSD sessions. The MSC retrieves the USSD information as part of the subscriber profile at the time of MS registration. The USSD transactions are carried between the USSD client in the MS and the USSD Gateway (GW) via the MSC.

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.

The new features and enhancements supported in this revision are:

• USSD messages may be sent over a paging channel; and

• USSD messages may be sent over an access channel.