6.2.12 Handling of network rejection not due to congestion control

The network may include a back-off timer value in a 5GS session management reject message to regulate the time interval at which the UE may retry the same procedure for 5GSM cause values other than #26 "insufficient resources", #28 "unknown PDU session type", #39 "reactivation requested", #46 "out of LADN service area", #50 "PDU session type IPv4 only allowed", #51 "PDU session type IPv6 only allowed", #54 "PDU session does not exist", #57 "PDU session type IPv4v6 only allowed", #58 "PDU session type Unstructured only allowed", #61 "PDU session type Ethernet only allowed", #67 "insufficient resources for specific slice and DNN", #68 "not supported SSC mode" and #69 "insufficient resources for specific slice". For 5GSM cause values other than #26 "insufficient resources", #28 "unknown PDU session type", #39 "reactivation requested", #46 "out of LADN service area", #54 "PDU session does not exist", #67 "insufficient resources for specific slice and DNN", #68 "not supported SSC mode", and #69 "insufficient resources for specific slice", and #86 "UAS services not allowed", the network may also include the re-attempt indicator to indicate whether the UE is allowed to re-attempt the corresponding session management procedure for the same DNN in S1 mode after inter-system change.

NOTE 1: In a PLMN, if the network includes this back-off timer value for 5GSM cause values other than #27 "missing or unknown DNN", then the UE is blocked from sending another 5GSM request for the same procedure for the same [PLMN, DNN, S-NSSAI], [PLMN, DNN, no S-NSSAI], [PLMN, no DNN, S-NSSAI], or [PLMN, no DNN, no S-NSSAI] combination for the specified duration. If the network includes this back-off timer value for 5GSM cause value #27 "missing or unknown DNN", then the UE is blocked from sending another 5GSM request for the same procedure for the same [PLMN, DNN], or [PLMN, no DNN] combination for the specified duration. In an SNPN, if the network includes this back-off timer value for 5GSM cause values other than #27 "missing or unknown DNN", then the UE is blocked from sending another 5GSM request for the same procedure for the same [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, DNN, S-NSSAI], [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, DNN, no S-NSSAI], [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, no DNN, S-NSSAI], or [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, no DNN, no S-NSSAI] combination for the specified duration. If the network includes this back-off timer value for 5GSM cause value #27 "missing or unknown DNN", then the UE is blocked from sending another 5GSM request for the same procedure for the same [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, DNN], or [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, no DNN] combination for the specified duration. Therefore, the operator needs to exercise caution in determining the use of this timer value.

NOTE 2: If the re-attempt indicator is not provided by the network, a UE registered in its HPLMN or in an EHPLMN can use the configured SM_RetryAtRATChange value specified in the NAS configuration MO or in the USIM NASCONFIG file to derive the re-attempt indicator as specified in clauses 6.4.1.4.3 and 6.4.2.4.3.

If re-attempt in S1 mode is allowed for 5GSM cause values other than #27 "missing or unknown DNN", the UE shall consider the back-off timer to be applicable only to the 5GS session management in N1 mode for the rejected 5GS session management procedure and the given [PLMN, DNN, S-NSSAI], [PLMN, DNN, no S-NSSAI], [PLMN, no DNN, S-NSSAI], or [PLMN, no DNN, no S-NSSAI] combination. If re-attempt in S1 mode is allowed for 5GSM cause value #27 "missing or unknown DNN", the UE shall consider the back-off timer to be applicable only to the 5GS session management in N1 mode for the rejected 5GS session management procedure and the given [PLMN, DNN], or [PLMN, no DNN] combination.If re-attempt in S1 mode is not allowed, the UE shall consider the back-off timer to be applicable to both NAS protocols, i.e. applicable to the 5GS session management in N1 mode for the rejected 5GS session management procedure and to the EPS session management in S1 mode for the corresponding session management procedure and the given [PLMN, DNN] or [PLMN, no DNN] combination.

NOTE 3: In the present clause the terms DNN and APN are referring to the same parameter.

In a PLMN, if the back-off timer was provided during the PDU session establishment procedure, the UE behaves as follows: for 5GSM cause values other than #27 "missing or unknown DNN", when the UE is registered in a HPLMN, the DNN and the S-NSSAI of the [PLMN, DNN, S-NSSAI] combination associated with the back-off timer is the DNN and the S-NSSAI provided by the UE when the PDU session is established. When the UE is registered in a VPLMN or in an EHPLMN where mapped S-NSSAI(s) are provided by the network as specified in clause 4.6.1, the DNN and the S-NSSAI of the [PLMN, DNN, S-NSSAI] combination associated with the back-off timer is the DNN and the mapped S-NSSAI provided by the UE when the PDU session is established. For 5GSM cause value #27 "missing or unknown DNN", the DNN of the [PLMN, DNN] combination associated with the back-off timer is the DNN provided by the UE when the PDU session is established. If no DNN or no S-NSSAI was provided to the network during the PDU session establishment, then the back-off timer is associated with the [PLMN, DNN, no S-NSSAI], [PLMN, no DNN, S-NSSAI], or [PLMN, no DNN, no S-NSSAI] combination, dependent on which parameters were provided for 5GSM cause values other than #27 "missing or unknown DNN". If no DNN was provided to the network during the PDU session establishment, then the back-off timer is associated with the [PLMN, no DNN] combination for 5GSM cause value #27 "missing or unknown DNN". For this purpose, the UE shall memorize the DNN and the S-NSSAI provided to the network during the PDU session establishment.

In a PLMN, if the back-off timer was provided during the PDU session modification procedure, the UE behaves as follows: the DNN associated with the back-off timer is the DNN, including no DNN, provided by the UE when the PDU session is established. If an S-NSSAI was provided by the UE during the PDU session establishment, when the UE is registered in a HPLMN, then the S-NSSAI associated with the back-off timer is the S-NSSAI of the PDU session. If an S-NSSAI was provided by the UE during the PDU session establishment, when the UE is registered in a VPLMN or in an EHPLMN where mapped S-NSSAI(s) are provided by the network as specified in clause 4.6.1, then the S-NSSAI associated with the back-off timer is the mapped S-NSSAI of the PDU session. If no S-NSSAI was provided by the UE during the PDU session establishment, then the back-off timer is associated with no S-NSSAI. For this purpose, the UE shall memorize the DNN and the S-NSSAI provided to the network during the PDU session establishment.

In a PLMN, the back-off timer associated with the [PLMN, no DNN, no S-NSSAI], or [PLMN, no DNN] combination will never be started due to any 5GSM procedure related to an emergency PDU session. If the back-off timer associated with the [PLMN, no DNN, no S-NSSAI], or [PLMN, no DNN] combination is running, it does not affect the ability of the UE to request an emergency PDU session.

In an SNPN, the back-off timer associated with the [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, no DNN, no S-NSSAI], or [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, no DNN] combination will never be started due to any 5GSM procedure related to an emergency PDU session. If the back-off timer associated with the back-off timer associated with the [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, no DNN, no S-NSSAI], or [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, no DNN] combination, it does not affect the ability of the UE to request an emergency PDU session.

In a PLMN, the network may additionally indicate in the re-attempt indicator that a command to back-off is applicable not only for the PLMN in which the UE received the 5GS session management reject message, but for each PLMN included in the equivalent PLMN list at the time when the 5GS session management reject message was received.

In an SNPN, the network may additionally indicate in the re-attempt indicator that a command to back-off is applicable not only for the SNPN in which the UE received the 5GS session management reject message, but for each SNPN included in the equivalent SNPN list at the time when the 5GS session management reject message was received.

In a PLMN, if the back-off timer is running or is deactivated for a given [PLMN, DNN, S-NSSAI], [PLMN, DNN, no S-NSSAI], [PLMN, no DNN, S-NSSAI], [PLMN, no DNN, no S-NSSAI], [PLMN, DNN], or [PLMN, no DNN] combination, and the UE is a UE configured for high priority access in selected PLMN, then the UE is allowed to initiate 5GSM procedures for the [PLMN, DNN, S-NSSAI], [PLMN, DNN, no S-NSSAI], [PLMN, no DNN, S-NSSAI], [PLMN, no DNN, no S-NSSAI], [PLMN, DNN], or [PLMN, no DNN] combination.

In an SNPN, if the back-off timer is running or is deactivated for a given [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, DNN, S-NSSAI], [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, DNN, no S-NSSAI], [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, no DNN, S-NSSAI], [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, no DNN, no S-NSSAI], [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, DNN], or [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, no DNN] combination if the UE is a UE configured for high priority access in selected SNPN, then the UE is allowed to initiate 5GSM procedures for the [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, DNN, S-NSSAI], [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, DNN, no S-NSSAI], [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, no DNN, S-NSSAI], [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, no DNN, no S-NSSAI], [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, DNN], or [SNPN, selected entry of the "list of subscriber data" or selected PLMN subscription, no DNN] combination.

The RATC bit in the re-attempt indicator IE and its derivation shall not be applicable in an SNPN.

If the network does not include a back-off timer with 5GSM cause #29 "user authentication or authorization failed", #31 "request rejected, unspecified", and #38 "network failure", the UE may use a local back-off timer that has exponential value or a default value, which is provisioned using implementation specific means, to:

• prevent sending the rejected 5GSM procedure for the respective DNN till its expiry; and
• allow sending the rejected 5GSM procedure for the respective DNN after its expiry.