PDU SESSION ESTABLISMENT REQUEST message is sent by the UE to the SMF to initiate establishment of a PDU session.

Bibliography:

1. https://medium.com/@jessica.chchuang/5g-urllc-always-on-pdu-session-1989aa1c2239
2. https://clcnetwork.wordpress.com/2020/04/19/5g-core-pdu-session-and-qos-part-2/
3. https://www.telecomhall.net/t/multiple-pdu-sessions/9237