3 Definitions and abbreviations

23.1723GPPRelease 17Stage 2Technical realization of Circuit Switched (CS) multimedia service UDI/RDI fallback and service modificationTS

3.1 Definitions

For the purposes of the present document, the terms and definitions given in 3GPP TR 21.905 [1] and the following apply:

fallback: when two services (multimedia and speech) are proposed but only one of them is available or wanted, only the service available (preferred or less preferred) is selected, and the other one is discarded

service change: when two services (multimedia and speech) are available during the active state of a call, users may request a service change to switch between the two services

3.2 Abbreviations

For the purposes of the present document, the abbreviations given in 3GPP TR 21.905 [1] and the following apply:

BC Bearer Capability

BC1 First Bearer Capability in a message (preferred service)

BC2 Second Bearer Capability in a message (less preferred service)

BCa Bearer Capability of the currently selected service

BCb Bearer Capability of the service to switch to

BCmm Bearer Capability multimedia

BCSM Basic Call State Model

BCsp Bearer Capability speech

CAMEL Customised Applications for Mobile network Enhanced Logic

DP Detection Point

IE Information Element

MMI Man-Machine Interface

O-MSC Originating MSC

OoBTC Out-of-Band Transcoder Control

O-UE Originating UE

RI Repeat Indicator

SCUDIF Service Change and UDI/RDI Fallback

T-MSC Terminating MSC

T-UE Terminating UE