PDU Session Modification Reject

If the SMF does not accept the request to modify the PDU session, it sets the 5GSM cause IE of the PDU Session Modification Reject message to indicate the reason for rejecting the PDU session modification procedure.

The SMF supports the following causes in the PDU Session Modification Reject message.

Reject Cause / 5GSM Cause

SMF Behavior

Cause #43 – Invalid PDU session identity

The SMF sends this cause when SMF does not have the session.

Protocol errors

Cause #95 – Semantically incorrect message

This 5GSM cause reports receipt of a message with semantically incorrect content.

Important
For mandatory parameters (PDU Session Identity and Procedure Transaction Identity) with non-semantical error also, the SMF sends this cause.