Unstructured Supplementary Service Data (USSD) using IP Multimedia (IM) Core Network (CN) subsystem IMS; Stage 3
The present document describes the procedures for using Unstructured Supplementary Service Data (USSD) operations for mobile initiated MMI mode over IP Multimedia Core Network Subsystem (IMS) and for network initiated MMI mode over IP Multimedia Core Network Subsystem (IMS). MMI mode is for the transparent transport of MMI strings entered by the user to the Application Servers (AS) and for the transparent transport of text strings back to the User Equipment (UE) to be displayed for user information. Support of either mode of USSD service is optional and only applicable for an operator's Public Land Mobile Network (PLMN).
The current version of the document describes procedures for USSD operation over IMS where the USSD application in the network resides on an AS. Signalling from the AS to other core network functional entities is left out of scope.
The present document is applicable to UE and AS which are intended to support USSD operations over IMS in mobile initiated MMI mode and network initiated MMI mode.