3GPP 23.501 v20.2.0 — the document's own text
5.16.4.8 IP Address Allocation
Taught in 21. Emergency calls, messages, voice and location (The 5G system architecture, in depth).
Emergency service is provided by the serving PLMN or SNPN. The UE and serving PLMN or SNPN must have compatible IP address versions in order for the UE to obtain a local emergency PDU Session.