6.2.8 Handling of S-NSSAI based congestion control

The network may detect and start performing S-NSSAI based congestion control when one or more S-NSSAI congestion criteria as specified in 3GPP TS 23.501 [8] are met. If the UE does not provide a DNN for a non-emergency PDU session, then the network uses the selected DNN. If the UE does not provide an S-NSSAI for a non-emergency PDU session, then the network uses the selected S-NSSAI.

In case of PLMN or SNPN, in the UE, 5GS session management timers T3584 for the S-NSSAI based congestion control are started and stopped on a per S-NSSAI, DNN and PLMN or SNPN basis. If the 5GSM congestion re-attempt indicator IE with the ABO bit set to "The back-off timer is applied in all PLMNs or equivalent SNPNs " is included in the 5GSM message with the 5GSM cause value #67 "insufficient resources for specific slice and DNN", then the UE applies the timer T3584 for all the PLMNs or all the equivalent SNPNs. Otherwise, the UE applies the timer T3584 for the registered PLMN or the registered SNPN. If the timer T3584 applies for all the PLMNs or all the equivalent SNPNs, the timer T3584 starts when the UE is registered in a VPLMN or an unsubscribed SNPN and the S-NSSAI is provided by the UE during the PDU session establishment, the timer T3584 is associated with the [mapped S-NSSAI, DNN] combination of the PDU session.

In case of PLMN or SNPN, in the UE, 5GS session management timers T3585 for the S-NSSAI based congestion control are started and stopped on a per S-NSSAI and PLMN or SNPN basis. If the 5GSM congestion re-attempt indicator IE with the ABO bit set to "The back-off timer is applied in all PLMNs or all equivalent SNPNs " is included in the 5GSM message with the 5GSM cause value #69 "insufficient resources for specific slice", then the UE applies the timer T3585 for all the PLMNs or all the equivalent SNPNs. Otherwise, the UE applies the timer T3585 for the registered PLMN or registered SNPN. If the timer T3585 applies for all the PLMNs or all the equivalent SNPNs, the timer T3585 starts when the UE is registered in a VPLMN or an unsubscribed SNPN and the S-NSSAI is provided by the UE during the PDU session establishment, the timer T3585 is associated with the mapped S-NSSAI of the PDU session. Additionally, if the 5GSM congestion re-attempt indicator IE with the CATBO bit set to "The back-off timer is applied in the current access type" is included in the 5GSM message with the 5GSM cause value #69 "insufficient resources for specific slice", then the UE applies the timer T3585 for the current access type. Otherwise, the UE applies the timer T3585 for both 3GPP access type and non-3GPP access type and the UE shall stop any running timer T3585 for the applied PLMN or SNPN and for the access different from the access from which the message is received.

In case of SNPN, if the UE does not support access to an SNPN using credentials from a credentials holder and equivalent SNPNs, in the UE 5GS session management timers T3584 for the S-NSSAI based congestion control are started and stopped on a per S-NSSAI, DNN and SNPN basis. If the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, in the UE 5GS session management timers T3584 for the S-NSSAI based congestion control are started and stopped on a per S-NSSAI, DNN, SNPN and selected entry of the "list of subscriber data" or selected PLMN subscription basis.

In case of SNPN, if the UE does not support access to an SNPN using credentials from a credentials holder and equivalent SNPNs, in the UE 5GS session management timers T3585 for the S-NSSAI based congestion control are started and stopped on a per S-NSSAI and SNPN basis. If the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, in the UE 5GS session management timers T3585 for the S-NSSAI based congestion control are started and stopped on a per S-NSSAI, SNPN and selected entry of the "list of subscriber data" or selected PLMN subscription basis.

If the timer T3584 or timer T3585 was provided during the PDU session establishment procedure, the S-NSSAI associated with T3584 or T3585, respectively is the S-NSSAI, including no S-NSSAI, provided by the UE during the PDU session establishment.

If the timer T3584 is provided during the PDU session modification or PDU session release procedure, the UE behaves as follows: The DNN associated with T3584 is the DNN provided by the UE during the PDU session establishment. If no S-NSSAI but DNN is provided by the UE along the PDU SESSION ESTABLISHMENT REQUEST message, then T3584 is associated with no S-NSSAI and the DNN provided to the network during the PDU session establishment. If the PDN connection was established when in the S1 mode, then T3584 is associated with no S-NSSAI. If no DNN but S-NSSAI is provided by the UE along the PDU SESSION ESTABLISHMENT REQUEST message, then T3584 is associated with no DNN and the S-NSSAI of the PDU session. If no DNN and no S-NSSAI is provided by the UE along the PDU SESSION ESTABLISHMENT REQUEST message, then T3584 is associated with no DNN and 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. The timer T3584 associated with no DNN and an S-NSSAI will never be started due to any 5GSM procedure related to an emergency PDU session. If the timer T3584 associated with no DNN and an S-NSSAI is running, it does not affect the ability of the UE to request an emergency PDU session.

If the timer T3585 was provided during the PDU session modification or PDU session release procedure, the UE behaves as follows: if an S-NSSAI was provided by the UE during the PDU session establishment, then T3585 is associated with the S-NSSAI of the PDU session. If no S-NSSAI is provided by the UE along the PDU SESSION ESTABLISHMENT REQUEST message, then T3585 is associated with no S-NSSAI. If the PDN connection was established when in the S1 mode, then T3585 is associated with no S-NSSAI.

If T3584 is running or is deactivated, then the UE is not allowed to initiate the:

• PDU session establishment procedure;
• PDU session modification procedure; or
• NAS transport procedure for sending CIoT user data;

for the respective [S-NSSAI, no DNN] or [S-NSSAI, DNN] combination unless the UE is a UE configured for high priority access in selected PLMN or SNPN or to report a change of 3GPP PS data off UE status.

In a PLMN, if the timer T3584 is running or is deactivated for all the PLMNs and is associated with an S-NSSAI other than no S-NSSAI, then

• the UE registered in the HPLMN or in an EHPLMN where mapped S-NSSAI(s) are not provided by the network as specified in clause 4.6.1 is not allowed to initiate the:
• PDU session establishment procedure;
• PDU session modification procedure; or
• NAS transport procedure for sending CIoT user data;

when the [S-NSSAI, no DNN] or [S-NSSAI, DNN] combination provided by the UE during the PDU session establishment is the same as the [S-NSSAI, no DNN] or [S-NSSAI, DNN] combination associated with the timer T3584 unless the UE is a UE configured for high priority access in selected PLMN or to report a change of 3GPP PS data off UE status; and

• the UE 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 is not allowed to initiate the:
• PDU session establishment procedure;
• PDU session modification procedure; or
• NAS transport procedure for sending CIoT user data;

when the [mapped S-NSSAI, no DNN] or [mapped S-NSSAI, DNN] combination provided by the UE during the PDU session establishment is the same as the [S-NSSAI, no DNN] or [S-NSSAI, DNN] combination associated with the timer T3584 unless the UE is a UE configured for high priority access in selected PLMN or to report a change of 3GPP PS data off UE status.

In a PLMN, if the timer T3584 is running or is deactivated for all the PLMNs and is associated with [no S-NSSAI, no DNN] or [no S-NSSAI, DNN] combination, then the UE is not allowed to initiate the:

• PDU session establishment procedure;
• PDU session modification procedure; or
• NAS transport procedure for sending CIoT user data;

for [no S-NSSAI, no DNN] or [no S-NSSAI, DNN] combination in any PLMN unless the UE is a UE configured for high priority access in selected PLMN or to report a change of 3GPP PS data off UE status.

In an SNPN, if the UE supports equivalent SNPNs, the timer T3584 is running or is deactivated for all the equivalent SNPNs, is associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, with an S-NSSAI other than no S-NSSAI, and with the RSNPN or an equivalent SNPN:

• the UE registered in the subscribed SNPN is not allowed to initiate the:
• PDU session establishment procedure; or
• PDU session modification procedure;

when the [S-NSSAI, no DNN] or [S-NSSAI, DNN] combination provided by the UE during the PDU session establishment is the same as the [S-NSSAI, no DNN] or [S-NSSAI, DNN] combination associated with the timer T3584 unless the UE is a UE configured for high priority access in the RSNPN or to report a change of 3GPP PS data off UE status; and

• the UE registered in a non-subscribed SNPN is not allowed to initiate the:
• PDU session establishment procedure; or
• PDU session modification procedure;

when the [mapped S-NSSAI, no DNN] or [mapped S-NSSAI, DNN] combination provided by the UE during the PDU session establishment is the same as the [S-NSSAI, no DNN] or [S-NSSAI, DNN] combination associated with the timer T3584 unless the UE is a UE configured for high priority access in RSNPN or to report a change of 3GPP PS data off UE status.

In an SNPN, if the UE supports equivalent SNPNs, the timer T3584 is running or is deactivated for all the equivalent SNPNs, is associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, with [no S-NSSAI, no DNN] or [no S-NSSAI, DNN] combination, and with the RSNPN or an equivalent SNPN, then the UE is not allowed to initiate the:

• PDU session establishment procedure; or
• PDU session modification procedure;

for [no S-NSSAI, no DNN] or [no S-NSSAI, DNN] combination unless the UE is a UE configured for high priority access in the RSPN or to report a change of 3GPP PS data off UE status.

If T3585 is running or is deactivated, then the UE is neither allowed to initiate the PDU session establishment procedure nor the PDU session modification procedure for the respective S-NSSAI unless the UE is a UE configured for high priority access in selected PLMN or SNPN or to report a change of 3GPP PS data off UE status.

In a PLMN, if the timer T3585 is running or is deactivated for all the PLMNs and is associated with an S-NSSAI other than no S-NSSAI, then

• the UE registered in the HPLMN or in an EHPLMN where mapped S-NSSAI(s) are not provided by the network as specified in clause 4.6.1 is not allowed to initiate the:
• PDU session establishment procedure;
• PDU session modification procedure; or
• NAS transport procedure for sending CIoT user data;

when the S-NSSAI provided by the UE during the PDU session establishment is the same as the S-NSSAI associated with timer T3585 unless the UE is a UE configured for high priority access in selected PLMNs or to report a change of 3GPP PS data off UE status; and

• the UE 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 is not allowed to initiate the:
• PDU session establishment procedure;
• PDU session modification procedure; or
• NAS transport procedure for sending CIoT user data;

when the mapped S-NSSAI provided by the UE during the PDU session establishment is the same as the S-NSSAI associated the timer T3585 unless the UE is a UE configured for high priority access in selected PLMN or to report a change of 3GPP PS data off UE status.

In a PLMN, if the timer T3585 is running or is deactivated for all the PLMNs and is associated with no S-NSSAI, then the UE is not allowed to initiate the:

• PDU session establishment procedure;
• PDU session modification procedure;
• NAS transport procedure for sending CIoT user data;

for no S-NSSAI in any PLMN unless the UE is a UE configured for high priority access in selected PLMN or to report a change of 3GPP PS data off UE status.

In an SNPN, if the UE supports equivalent SNPNs, the timer T3585 is running or is deactivated for all the equivalent SNPNs, is associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, with an S-NSSAI other than no S-NSSAI, and with the RSNPN or an equivalent SNPN:

• the UE registered in the subscribed SNPN is not allowed to initiate the:
• PDU session establishment procedure; or
• PDU session modification procedure;

when the S-NSSAI provided by the UE during the PDU session establishment is the same as the S-NSSAI associated with timer T3585 unless the UE is a UE configured for high priority access in the RSNPN or to report a change of 3GPP PS data off UE status; and

• the UE registered in a non-subscribed SNPN is not allowed to initiate the:
• PDU session establishment procedure; or
• PDU session modification procedure;

when the mapped S-NSSAI provided by the UE during the PDU session establishment is the same as the S-NSSAI associated the timer T3585 unless the UE is a UE configured for high priority access in the RSNPN or to report a change of 3GPP PS data off UE status.

In an SNPN, if the UE supports equivalent SNPNs, the timer T3585 is running or is deactivated for all the equivalent SNPNs, is associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, with no S-NSSAI, and with the RSNPN or an equivalent SNPN, then the UE is not allowed to initiate the:

• PDU session establishment procedure; or
• PDU session modification procedure;

for no S-NSSAI unless the UE is a UE configured for high priority access in RSNPN or to report a change of 3GPP PS data off UE status.

If the network does not include timer T3584 with 5GSM cause #67 "insufficient resources for specific slice and DNN", 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 any 5GSM procedure for the respective DNN and S-NSSAI till its expiry; and
• allow sending any 5GSM procedure for the respective DNN and S-NSSAI after its expiry.

If the network does not include timer T3585 with 5GSM cause #69 "insufficient resources for specific slice", 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 any 5GSM procedure for the respective S-NSSAI till its expiry; and
• allow sending any 5GSM procedure for the respective S-NSSAI after its expiry.