Question: What action does the network take when it receives a PDU SESSION MODIFICATION COMPLETE message with an unknown or unforeseen Procedure Transaction Identity (PTI) value?
Option 1: The network responds with a 5GSM STATUS message including 5GSM cause #81 "invalid PTI value".
Option 2: The network ignores the message.
Option 3: The network responds with a 5GSM STATUS message including 5GSM cause #47 "PTI mismatch".
Option 4: The network sends a PDU SESSION RELEASE COMMAND message.
Explanation: According to the specified procedure, when the network receives a PDU SESSION MODIFICATION COMPLETE message with an unknown or unforeseen PTI value, it responds with a 5GSM STATUS message including 5GSM cause #47 "PTI mismatch". This is because the PTI value does not match any PTI in use.