3GPP 23.501 v20.2.0 — the document's own text
5.16.4.7 PCC for Emergency Services
Taught in 21. Emergency calls, messages, voice and location (The 5G system architecture, in depth).
Dynamic PCC is used for UEs establishing emergency service and shall be used to manage IMS emergency sessions when an operator allows IMS emergency sessions. When establishing Emergency Services with a SMF, the PCF provides the SMF with the QoS parameters, including an ARP value reserved for the Emergency Services to prioritize the QoS Flows when performing admission control, as defined in TS 23.503 [45].
The PCF rejects an IMS session established via the emergency PDU Session if the AF (i.e. P-CSCF) does not provide an emergency indication to the PCF.