Question: What should the SMF do if it receives a PDU SESSION MODIFICATION REQUEST message for an emergency PDU session without the 5GSM cause IE or with a 5GSM cause other than #41, #42, #44, #45, #83, #84, and #85?
Option 1: The SMF should accept the request and modify the PDU session accordingly.
Option 2: The SMF should reject the request with 5GSM cause #31 "request rejected, unspecified".
Option 3: The SMF should set the 5GSM cause IE to #43 "Invalid PDU session identity" in the PDU SESSION MODIFICATION REJECT message.
Option 4: The SMF should forward the request to the AMF for further processing.
Explanation: According to the text, if the PDU session is an emergency PDU session and the 5GSM cause IE is not included in the PDU SESSION MODIFICATION REQUEST message or is set to a 5GSM cause other than #41, #42, #44, #45, #83, #84, and #85, the SMF shall reject the PDU SESSION MODIFICATION REQUEST message with 5GSM cause #31 "request rejected, unspecified".