PDU Session Establishment Reject

If the connectivity with the requested DN is rejected by the network, SMF sets the 5GSM cause IE of the PDU Session Establishment Reject message to indicate the reason for rejecting the PDU Session Establishment procedure.

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

Reject Cause / 5GSM Cause

SMF Behavior

Cause #26 – insufficient resources

The SMF includes this cause when it receives N2SmInfoType with "PDU_RES_SETUP_FAIL" along with any of the following N2 causes:

  • RadioNetwork/Radio_resources_not_available

  • RadioNetwork/Failure_in_the_radio_interface_procedure

  • Misc/Not_enough_user_plane_processing_resources

Cause #27 – missing or unknown DNN

The SMF includes this cause when DNN is not present in SmContextCreateData even though it is required and not configured in SMF.

Cause #28 – unknown PDU session type

The SMF includes this cause when the PDU Session Establishment Request message includes a PDU session type that is not supported by SMF.

Cause #29 – user authentication or authorization failed

The SMF includes this cause when DN authentication of the UE was performed and completed unsuccessfully (Radius Authentication Timeout).

Cause #32 – service option not supported

The SMF supports this cause when the validation of received S-NSSAI fails against the allowed list of S-NSSAI.

Cause #33 – requested service option not subscribed

The SMF supports this cause when the UE requests a service option for which it has no subscription.

Cause #38 – network failure

The SMF supports this cause when the requested service was rejected due to an error in the network. This includes any internal failures or no response from any external NF during the PDN-setup procedure.

Cause #54 – PDU session does not exist

The SMF supports this cause when it does not have any information about the PDU session which is requested by the UE to transfer between 3GPP access and non-3GPP access or from the EPS to the 5GS.

Cause #70 – missing or unknown DNN in a slice

The SMF supports this cause when the slice configuration is present but the requested DNN is not configured under the slice in the SMF.

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.