6 MMI aspects
22.1533GPPMultimedia priority serviceRelease 19TS
In the case when MPS invocation is based on the presence of an MPS-specific service code entered by the originating Service User, this specific service code must be defined for the 3GPP network to recognize such an invocation.
The 3GPP network supporting on-demand invocation of MPS shall recognize a service code indicating a request for MPS.
NOTE: A Service User roaming within or outside the home country must use an MPS-specific service code recognized by the visited PLMN, to indicate a request for MPS based on the agreements between the home and visited PLMNs for MPS.
The choice of an MPS-specific service code is a regional/national and operator matter.