This document defines radio interface support for USSD in cdma2000^®1 Spread Spectrum Systems.

supplementary service data (USSD) allows the Mobile Station (MS) user and a PLMN operator defined application to communicate in a way which is transparent to the MS and to intermediate network entities. The mechanism allows development of PLMN specific supplementary services.

There are two modes of USSD: MMI-mode and application mode. MMI-mode USSD is for the transparent transport of MMI strings entered by the user to the network and for the transparent transport of text strings from the network that are displayed by the mobile for user information.

Application mode USSD is for the transparent transport of data between the network and the UE. Application mode USSD is intended to be used by applications in the network and their peer applications in the UE.

USSD may be initiated by the MS user, or by the network. Unlike Short Message Service (SMS) messages, USSD messages create a real-time connection during a USSD session. The connection remains open, allowing a two-way exchange of a sequence of data. Several examples of how USSD Services are used include: Prepaid balance Inquiry, Balance Transfer (payment from one's balance to another balance), Voting ("Please rate our customer service: 1=Good, 2=OK, 3=Bad" after a call to a Customer Service Center), and Call Me (requesting another party to call you).

¹ cdma2000® is the trademark for the technical nomenclature for certain specifications and standards of the Organizational Partners (OPs) of 3GPP2. Geographically (and as of the date of publication), cdma2000® is a registered trademark of the Telecommunications Industry Association (TIA-USA) in the United States.