5GSM Cause Handling
Feature Summary and Revision History
- Feature Summary
- Revision History
Feature Description
How it Works
- Standards Compliance
Configuring the 5GSM Cause Handling Feature
- 5GSM Cause Handling OAM Support
  - Statistics

5GSM Cause Handling

Feature Summary and Revision History

Feature Summary


Applicable Product(s) or Functional Area	SMF
Applicable Platform(s)	SMI
Feature Default Setting	Enabled - Always-on
Related Changes in this Release	Not Applicable
Related Documentation	Not Applicable

Revision History

Table 1. Revision History
Revision Details	Release
First introduced.	2020.02.0

Feature Description

The SMF supports 5GSM cause handling for the UE and Network initiated procedures.

The procedures include:

PDU-Session-Establishment
PDU-Session-Modification
PDU-Session-Release

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.

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.

PDU Session Release Reject

If the SMF does not accept the request to release the PDU session, SMF sets the 5GSM Cause IE of the PDU Session Release Reject message to indicate the reason for rejecting the PDU session release.

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

Reject Cause / 5GSM Cause

SMF Behavior

Cause #43 – Invalid PDU session identity

The SMF supports 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.

PDU Session Release Request

To initiate the UE-requested PDU Session Release procedure, UE sends the PDU Session Release Request message with the 5GSM Cause IE to indicate the reason for releasing the PDU session.

The SMF supports the following causes in the PDU Session Release Request message.


Reject Cause / 5GSM Cause	SMF Behavior
Cause #36 – regular deactivation	The SMF retains the statistics based on the cause and continues with the Release procedure.
Cause #41 – Semantic error in the TFT operation	The SMF retains the statistics based on the cause and continues with the Release procedure.
Cause #42 – Syntactical error in the TFT operation	The SMF retains the statistics based on the cause and continues with the Release procedure.
Cause #44 – Semantic errors in packet filter(s)	The SMF retains the statistics based on the cause and continues with the Release procedure.
Cause #45 – Syntactical errors in packet filter(s)	The SMF retains the statistics based on the cause and continues with the Release procedure.

PDU Session Modification Command Reject

If the UE rejects the PDU-Session-Modification-Command, it sets the 5GSM cause IE of the PDU Session Modification Reject message to indicate the reason for rejecting the PDU session modification.

The SMF supports the following 5GSM causes.


5GSM Cause	SMF Behavior
Cause #26 – insufficient resources	The SMF retains the statistics based on the cause.
Cause #43 – Invalid PDU session identity	The SMF retains the statistics based on the cause and releases the existing PDU session.
Cause #44 – Semantic error in packet filter(s)	The SMF retains the statistics based on the cause.
Cause #45 – Syntactical error in packet filter(s)	The SMF retains the statistics based on the cause.
Cause #83 – Semantic error in the QoS operation	The SMF retains the statistics based on the cause.
Cause #85 – Syntactical error in the QoS operation	The SMF retains the statistics based on the cause.

How it Works

The SMF supports 5GSM cause handling for the PDU-Session-Establishment, PDU-Session-Modification and PDU-Session-Release procedures. An appropriate SM cause will be sent over the N1 message to the UE.

Standards Compliance

The 5GSM Cause Handling feature complies with the 3GPP TS 24.501, version 15.4.0, Release 15 (Non-Access-Stratum (NAS) protocol for 5G System (5GS)).

Configuring the 5GSM Cause Handling Feature