This service is available to
UDI/RDI multimedia calls and allows users to achieve successful call establishment when end to end circuit-switched (CS) multimedia is not possible (fallback to speech) or when signalling of the feature is not possible in the network (fallback to preferred service or speech). Furthermore, it allows the users to swap between a multimedia service and
basic speech during an established call.
full Table of Contents for TS 23.172 Word version: 15.0.0