Section: 6.4.2.4.2 Handling of network rejection due to congestion control
Content: If: - the 5GSM cause value #26 "insufficient resources" and the Back-off timer value IE are included in the PDU SESSION MODIFICATION REJECT message; or - an indication that the 5GSM message was not forwarded due to DNN based congestion control is received along a Back-off timer value and a PDU SESSION MODIFICATION REQUEST message with the PDU session ID IE set to the PDU session ID of the PDU session; the UE shall ignore the Re-attempt indicator IE or the 5GSM congestion re-attempt indicator IE provided by the network, if any, and the UE shall take different actions depending on the timer value received for timer T3396 in the Back-off timer value IE or depending on the Back-off timer value received from the 5GMM sublayer (if the UE is a UE configured for high priority access in selected PLMN or SNPN, exceptions are specified in subclause 6.2.7): a) If the timer value indicates neither zero nor deactivated and a DNN was provided during the PDU session establishment, the UE shall stop timer T3396 associated with the corresponding DNN, if it is running. If the timer value indicates neither zero nor deactivated and no DNN was provided during the PDU session establishment and the request type was different from "initial emergency request" and different from "existing emergency PDU session", the UE shall stop timer T3396 associated with no DNN if it is running. In an SNPN, the timer T3396 to be stopped includes: 1) the timer T3396 applied for all the equivalent SNPNs, and associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and 2) the timer T3396 applied for the registered SNPN, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. The UE shall then start timer T3396 with the value provided in the Back-off timer value IE or with the Back-off timer value received from the 5GMM sublayer and: 1) shall not send another PDU SESSION ESTABLISHMENT REQUEST message, or PDU SESSION MODIFICATION REQUEST message with exception of those identified in subclause 6.4.2.1, for the same DNN that was sent by the UE, until timer T3396 expires or timer T3396 is stopped; and 2) shall not send another PDU SESSION ESTABLISHMENT REQUEST message without a DNN and with request type different from "initial emergency request" and different from "existing emergency PDU session", or another PDU SESSION MODIFICATION REQUEST message with exception of those identified in subclause 6.4.2.1, for a non-emergency PDU session established without a DNN provided by the UE, if no DNN was provided during the PDU session establishment and the request type was different from "initial emergency request" and different from "existing emergency PDU session", until timer T3396 expires or timer T3396 is stopped. The UE shall not stop timer T3396 upon a PLMN change, SNPN change, or inter-system change. b) if the timer value indicates that this timer is deactivated and a DNN was provided during the PDU session establishment, the UE shall stop timer T3396 associated with the corresponding DNN, if it is running. If the timer value indicates that this timer is deactivated and no DNN was provided during the PDU session establishment and the request type was different from "initial emergency request" and different from "existing emergency PDU session", the UE shall stop timer T3396 associated with no DNN if it is running. In an SNPN, the timer T3396 to be stopped includes: 1) the timer T3396 applied for all the equivalent SNPNs, and associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and 2) the timer T3396 applied for the registered SNPN, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. The UE: 1) shall not send another PDU SESSION ESTABLISHMENT REQUEST message or PDU SESSION MODIFICATION REQUEST with exception of those identified in subclause 6.4.2.1, for the same DNN until the UE is switched off, the USIM is removed, the entry in the "list of subscriber data" for the current SNPN is updated, or the UE receives a PDU SESSION MODIFICATION COMMAND message for the same DNN from the network, or a PDU SESSION AUTHENTICATION COMMAND message for the same DNN from the network, or a PDU SESSION RELEASE COMMAND message without the Back-off timer value IE for the same DNN from the network; and 2) shall not send another PDU SESSION ESTABLISHMENT REQUEST message without a DNN and with request type different from "initial emergency request" and different from "existing emergency PDU session", or another PDU SESSION MODIFICATION REQUEST message with exception of those identified in subclause 6.4.2.1, for a non-emergency PDU session established without a DNN provided by the UE, if no DNN was provided during the PDU session establishment and the request type was different from "initial emergency request" and different from "existing emergency PDU session", until the UE is switched off, the USIM is removed, the entry in the "list of subscriber data" for the current SNPN is updated, or the UE receives a PDU SESSION MODIFICATION COMMAND message for a non-emergency PDU session established without a DNN provided by the UE, a PDU SESSION AUTHENTICATION COMMAND message for a non-emergency PDU session established without a DNN provided by the UE, or a PDU SESSION RELEASE COMMAND message without the Back-off timer value IE for a non-emergency PDU session established without a DNN provided by the UE. The timer T3396 remains deactivated upon a PLMN change, SNPN change, or inter-system change. c) if the timer value indicates zero, the UE: 1) shall stop timer T3396 associated with the corresponding DNN, if running. In an SNPN, the timer T3396 to be stopped includes: i) the timer T3396 applied for all the equivalent SNPNs, and associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and ii) the timer T3396 applied for the registered SNPN, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. The UE may send another PDU SESSION ESTABLISHMENT REQUEST message or PDU SESSION MODIFICATION REQUEST message for the same DNN; and 2) if no DNN was provided during the PDU session establishment and the request type was different from "initial emergency request" and different from "existing emergency PDU session", the UE shall stop timer T3396 associated with no DNN, if running. In an SNPN, the timer T3396 to be stopped includes: i) the timer T3396 applied for all the equivalent SNPNs, and associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and ii) the timer T3396 applied for the registered SNPN, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. The UE may send another PDU SESSION ESTABLISHMENT REQUEST message without a DNN, or another PDU SESSION MODIFICATION REQUEST message without a DNN provided by the UE. In an SNPN, if the UE supports equivalent SNPNs then the UE shall apply the timer T3396 for all the equivalent SNPNs. Otherwise, the UE shall apply the timer T3396 for the registered SNPN. If the Back-off timer value IE is not included or no Back-off timer value is received from the 5GMM sublayer, then the UE may send another PDU SESSION ESTABLISHMENT REQUEST message or PDU SESSION MODIFICATION REQUEST message for the same DNN or without a DNN. If the timer T3396 is running when the UE enters state 5GMM-DEREGISTERED, the UE remains switched on, and the USIM in the UE (if any) remains the same and the entry in the "list of subscriber data" for the SNPN to which timer T3396 is associated (if any) is not updated, then timer T3396 is kept running until it expires or it is stopped When the timer T3396 is running or the timer is deactivated, the UE is allowed to initiate a PDU session establishment procedure for emergency services. If the UE is switched off when the timer T3396 is running, and if the USIM in the UE (if any) remains the same and the entry in the "list of subscriber data" for the SNPN to which timer T3396 is associated (if any) is not updated when the UE is switched on, the UE shall behave as follows: - let t1 be the time remaining for T3396 timeout at switch off and let t be the time elapsed between switch off and switch on. If t1 is greater than t, then the timer shall be restarted with the value t1 – t. If t1 is equal to or less than t, then the timer need not be restarted. If the UE is not capable of determining t, then the UE shall restart the timer with the value t1. If the UE is a UE operating in single-registration mode in a network supporting N26 interface and the PDU SESSION MODIFICATION REQUEST message was sent for a PDN connection established when in S1 mode after an inter-system change from S1 mode to N1 mode and timer T3396 associated with the corresponding DNN (or no DNN) is running, then the UE shall re-initiate the UE-requested PDU session modification procedure after expiry of timer T3396. If: - the 5GSM cause value #67 "insufficient resources for specific slice and DNN" and the Back-off timer value IE are included in the PDU SESSION MODIFICATION REJECT message; or - an indication that the 5GSM message was not forwarded due to S-NSSAI and DNN based congestion control is received along a Back-off timer value and a PDU SESSION MODIFICATION REQUEST message with the PDU session ID IE set to the PDU session ID of the PDU session; the UE shall ignore the Re-attempt indicator IE provided by the network, if any, and take different actions depending on the timer value received for timer T3584 in the Back-off timer value IE or depending on the Back-off timer value received from the 5GMM sublayer (if the UE is a UE configured for high priority access in selected PLMN or SNPN, exceptions are specified in subclause 6.2.8): a) If the timer value indicates neither zero nor deactivated, and both an S-NSSAI and a DNN were provided by the UE during the PDU session establishment, the UE shall stop timer T3584 associated with the [S-NSSAI of the PDU session, DNN] combination, if it is running. If the timer value indicates neither zero nor deactivated, an S-NSSAI and no DNN was provided during the PDU session establishment and the request type was different from "initial emergency request" and different from "existing emergency PDU session", the UE shall stop timer T3584 associated with [S-NSSAI of the PDU session, no DNN] combination, if it is running. If the timer value indicates neither zero nor deactivated, no S-NSSAI and a DNN was provided during the PDU session establishment, the UE shall stop timer T3584 associated with the [no S-NSSAI, DNN] combination, if it is running. If the timer value indicates neither zero nor deactivated and neither S-NSSAI nor DNN was provided during the PDU session establishment and the request type was different from "initial emergency request" and different from "existing emergency PDU session", the UE shall stop timer T3584 associated with the [no S-NSSAI, no DNN] combination, if it is running. The timer T3584 to be stopped includes: 1) in a PLMN: i) the timer T3584 applied for all the PLMNs, if running; and ii) the timer T3584 applied for the registered PLMN, if running; or 2) in an SNPN: i) the timer T3584 applied for all the equivalent SNPNs, and associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and ii) the timer T3584 applied for the registered SNPN, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. The UE shall then start timer T3584 with the value provided in the Back-off timer value IE or with the Back-off timer value received from the 5GMM sublayer and: 1) shall not send another PDU SESSION ESTABLISHMENT REQUEST message or PDU SESSION MODIFICATION REQUEST message with the exception of those identified in subclause 6.4.2.1, for the [S-NSSAI, DNN] combination, until timer T3584 expires or timer T3584 is stopped; 2) shall not send another PDU SESSION ESTABLISHMENT REQUEST message with request type different from "initial emergency request" and different from "existing emergency PDU session", or another PDU SESSION MODIFICATION REQUEST message with the exception of those identified in subclause 6.4.2.1, for the [S-NSSAI of the PDU session, no DNN] combination, if no DNN was provided during the PDU session establishment, until timer T3584 expires or timer T3584 is stopped; 3) shall not send another PDU SESSION ESTABLISHMENT REQUEST message, or another PDU SESSION MODIFICATION REQUEST message with the exception of those identified in subclause 6.4.2.1, for the [no S-NSSAI, DNN] combination, if no S-NSSAI was provided during the PDU session establishment, until timer T3584 expires or timer T3584 is stopped; and 4) shall not send another PDU SESSION ESTABLISHMENT REQUEST message with request type different from "initial emergency request" and different from "existing emergency PDU session", or another PDU SESSION MODIFICATION REQUEST message with the exception of those identified in subclause 6.4.2.1, for the [no S-NSSAI, no DNN] combination, if neither S-NSSAI nor DNN was provided during the PDU session establishment, until timer T3584 expires or timer T3584 is stopped. The UE shall not stop timer T3584 upon a PLMN change, SNPN change, or inter-system change; b) if the timer value indicates that this timer is deactivated: 1) if both S-NSSAI and DNN were provided by the UE during the PDU session establishment, the UE shall stop timer T3584 associated with the [S-NSSAI of the PDU session, DNN] combination, if running. The timer T3584 to be stopped includes: i) in a PLMN: A) the timer T3584 applied for all the PLMNs, if running; and B) the timer T3584 applied for the registered PLMN, if running; or ii) in an SNPN: A) the timer T3584 applied for all the equivalent SNPNs, and associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and B) the timer T3584 applied for the registered SNPN, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. The UE shall not send another PDU SESSION ESTABLISHMENT REQUEST message or PDU SESSION MODIFICATION REQUEST message with exception of those identified in subclause 6.4.2.1, for the [S-NSSAI of the PDU session, DNN] combination that was sent by the UE, until the UE is switched off, the USIM is removed, the entry in the "list of subscriber data" for the current SNPN is updated, or the UE receives a PDU SESSION MODIFICATION COMMAND message for the [S-NSSAI of the PDU session, DNN] combination from the network, or a PDU SESSION AUTHENTICATION COMMAND message for the [S-NSSAI of the PDU session, DNN] combination from the network, or a PDU SESSION RELEASE COMMAND message without the Back-off timer value IE for the [S-NSSAI of the PDU session, DNN] combination from the network; 2) if an S-NSSAI was provided but a DNN was not provided by the UE during the PDU session establishment, the UE shall stop timer T3584 associated with the [S-NSSAI of the PDU session, no DNN] combination, if running. The timer T3584 to be stopped includes: i) in a PLMN: A) the timer T3584 applied for all the PLMNs, if running; and B) the timer T3584 applied for the registered PLMN, if running; or ii) in an SNPN: A) the timer T3584 applied for all the equivalent SNPNs, and associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and B) the timer T3584 applied for the registered SNPN, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. The UE shall not send a PDU SESSION ESTABLISHMENT REQUEST message with request type different from "initial emergency request" and different from "existing emergency PDU session", or a PDU SESSION MODIFICATION REQUEST message with exception of those identified in subclause 6.4.2.1, for the [S-NSSAI of the PDU session, no DNN] combination, if no DNN was provided during the PDU session establishment, until the UE is switched off, the USIM is removed, the entry in the "list of subscriber data" for the current SNPN is updated, or the UE receives a PDU SESSION MODIFICATION COMMAND message for a non-emergency PDU session established for the [S-NSSAI of the PDU session, no DNN] combination from the network, or a PDU SESSION AUTHENTICATION COMMAND message for a non-emergency PDU session established for the [S-NSSAI of the PDU session, no DNN] combination from the network, or a PDU SESSION RELEASE COMMAND message without the Back-off timer value IE for a non-emergency PDU session established for the [S-NSSAI of the PDU session, no DNN] combination from the network; 3) if an S-NSSAI was not provided but a DNN was provided by the UE during the PDU session establishment, the UE shall stop timer T3584 associated with the [no S-NSSAI, DNN] combination, if running. The timer T3584 to be stopped includes: i) in a PLMN: A) the timer T3584 applied for all the PLMNs, if running; and B) the timer T3584 applied for the registered PLMN, if running; or ii) in an SNPN: A) the timer T3584 applied for all the equivalent SNPNs, and associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and B) the timer T3584 applied for the registered SNPN, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. The UE shall not send a PDU SESSION ESTABLISHMENT REQUEST message, or a PDU SESSION MODIFICATION REQUEST message with exception of those identified in subclause 6.4.2.1, for the [no S-NSSAI, DNN] combination, if no S-NSSAI was provided during the PDU session establishment, until the UE is switched off, the USIM is removed, the entry in the "list of subscriber data" for the current SNPN is updated, or the UE receives a PDU SESSION MODIFICATION COMMAND message for the [no S-NSSAI, DNN] combination from the network, or a PDU SESSION AUTHENTICATION COMMAND message for the [no S-NSSAI, DNN] combination from the network, or a PDU SESSION RELEASE COMMAND message without the Back-off timer value IE for the [no S-NSSAI, DNN] combination from the network; and 4) if neither S-NSSAI nor DNN were provided by the UE during the PDU session establishment, the UE shall stop timer T3584 associated with the [no S-NSSAI, no DNN] combination, if running. The timer T3584 to be stopped includes: i) in a PLMN: A) the timer T3584 applied for all the PLMNs, if running; and B) the timer T3584 applied for the registered PLMN, if running; or ii) in an SNPN: A) the timer T3584 applied for all the equivalent SNPNs, and associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and B) the timer T3584 applied for the registered SNPN, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. The UE shall not send a PDU SESSION ESTABLISHMENT REQUEST message with request type different from "initial emergency request" and different from "existing emergency PDU session", or a PDU SESSION MODIFICATION REQUEST message with exception of those identified in subclause 6.4.2.1, for the [no S-NSSAI, no DNN] combination, if neither S-NSSAI nor DNN was provided during the PDU session establishment, until the UE is switched off, the USIM is removed, the entry in the "list of subscriber data" for the current SNPN is updated, or the UE receives a PDU SESSION MODIFICATION COMMAND message for a non-emergency PDU session established for the [no S-NSSAI, no DNN] combination from the network, or a PDU SESSION AUTHENTICATION COMMAND message for a non-emergency PDU session established for the [no S-NSSAI, no DNN] combination from the network, or a PDU SESSION RELEASE COMMAND message without the Back-off timer value IE for a non-emergency PDU session established for the [no S-NSSAI, no DNN] combination from the network. The timer T3584 remains deactivated upon a PLMN change, SNPN change, or inter-system change; and c) if the timer value indicates zero: 1) if both S-NSSAI and DNN were provided by the UE during the PDU session establishment, the UE shall stop timer T3584 associated with the [S-NSSAI of the PDU session, DNN] combination, if running. The timer T3584 to be stopped includes: i) in a PLMN: A) the timer T3584 applied for all the PLMNs, if running; and B) the timer T3584 applied for the registered PLMN, if running; or ii) in an SNPN: A) the timer T3584 applied for all the equivalent SNPNs, and associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and B) the timer T3584 applied for the registered SNPN, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. The UE may send another PDU SESSION ESTABLISHMENT REQUEST message or PDU SESSION MODIFICATION REQUEST message for the [S-NSSAI of the PDU session, DNN] combination; 2) if an S-NSSAI was provided but a DNN was not provided by the UE during the PDU session establishment, the UE shall stop timer T3584 associated with the [S-NSSAI of the PDU session, no DNN] combination, if running. The timer T3584 to be stopped includes: i) in a PLMN: A) the timer T3584 applied for all the PLMNs, if running; and B) the timer T3584 applied for the registered PLMN, if running; or ii) in an SNPN: A) the timer T3584 applied for all the equivalent SNPNs, and associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and B) the timer T3584 applied for the registered SNPN, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. The UE may send another PDU SESSION ESTABLISHMENT REQUEST message, or PDU SESSION MODIFICATION REQUEST message for the [S-NSSAI of the PDU session, no DNN] combination if the request type was different from "initial emergency request" and different from "existing emergency PDU session"; 3) if an S-NSSAI was not provided but a DNN was provided by the UE during the PDU session establishment, the UE shall stop timer T3584 associated with the [no S-NSSAI, DNN] combination, if running. The timer T3584 to be stopped includes: i) in a PLMN: A) the timer T3584 applied for all the PLMNs, if running; and B) the timer T3584 applied for the registered PLMN, if running; or ii) in an SNPN: A) the timer T3584 applied for all the equivalent SNPNs, and associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and B) the timer T3584 applied for the registered SNPN, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. The UE may send another PDU SESSION ESTABLISHMENT REQUEST message, or PDU SESSION MODIFICATION REQUEST message for the [no S-NSSAI, DNN] combination; and 4) if neither S-NSSAI nor DNN were provided by the UE during the PDU session establishment, the UE shall stop timer T3584 associated with the [no S-NSSAI, no DNN] combination, if running. The timer T3584 to be stopped includes: i) in a PLMN: A) the timer T3584 applied for all the PLMNs, if running; and B) the timer T3584 applied for the registered PLMN, if running; or ii) in an SNPN: A) the timer T3584 applied for all the equivalent SNPNs, and associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and B) the timer T3584 applied for the registered SNPN, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. The UE may send another PDU SESSION ESTABLISHMENT REQUEST message, or PDU SESSION MODIFICATION REQUEST message for the [no S-NSSAI, no DNN] combination and the request type was different from "initial emergency request" and different from "existing emergency PDU session". 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 PDU SESSION MODIFICATION REJECT message with the 5GSM cause value #67 "insufficient resources for specific slice and DNN", then the UE shall apply the timer T3584 for all the PLMNs or all the equivalent SNPNs. Otherwise, the UE shall apply the timer T3584 for the registered PLMN or the registered SNPN. If the Back-off timer value IE is not included or no Back-off timer value is received from the 5GMM sublayer, then the UE may send another PDU SESSION ESTABLISHMENT REQUEST message or PDU SESSION MODIFICATION REQUEST message for the same [S-NSSAI, DNN] combination, or for the same [S-NSSAI, no DNN] combination, or for the same [no S-NSSAI, DNN] combination, or for the same [no S-NSSAI, no DNN] combination. When the timer T3584 is running or the timer is deactivated, the UE is allowed to initiate a PDU session establishment procedure for emergency services. If the timer T3584 is running when the UE enters state 5GMM-DEREGISTERED, the UE remains switched on, and the USIM in the UE (if any) remains the same and the entry in the "list of subscriber data" for the SNPN to which timer T3584 is associated (if any) is not updated, then timer T3584 is kept running until it expires or it is stopped. If the UE is switched off when the timer T3584 is running, and if the USIM in the UE (if any) remains the same and the entry in the "list of subscriber data" for the SNPN to which timer T3584 is associated (if any) is not updated when the UE is switched on, the UE shall behave as follows: - let t1 be the time remaining for T3584 timeout at switch off and let t be the time elapsed between switch off and switch on. If t1 is greater than t, then the timer shall be restarted with the value t1 – t. If t1 is equal to or less than t, then the timer need not be restarted. If the UE is not capable of determining t, then the UE shall restart the timer with the value t1. If the UE is a UE operating in single-registration mode in a network supporting N26 interface and the PDU SESSION MODIFICATION REQUEST message was sent for a PDN connection established when in S1 mode after an inter-system change from S1 mode to N1 mode and timer T3584 associated with the corresponding [no S-NSSAI, DNN] combination or [no S-NSSAI, no DNN] combination is running, then the UE shall re-initiate the UE-requested PDU session modification procedure after expiry of timer T3584. If: - the 5GSM cause value #69 "insufficient resources for specific slice" and the Back-off timer value IE are included in the PDU SESSION MODIFICATION REJECT message; or - an indication that the 5GSM message was not forwarded due to S-NSSAI only based congestion control is received along a Back-off timer value and a PDU SESSION MODIFICATION REQUEST message with the PDU session ID IE set to the PDU session ID of the PDU session; the UE shall ignore the bit "RATC" and the bit "EPLMNC" in the Re-attempt indicator IE provided by the network, if any, and take different actions depending on the timer value received for timer T3585 in the Back-off timer value IE or depending on the Back-off timer value received from the 5GMM sublayer (if the UE is a UE configured for high priority access in selected PLMN or SNPN, exceptions are specified in subclause 6.2.8): a) If the timer value indicates neither zero nor deactivated and an S-NSSAI was provided during the PDU session establishment and the request type was different from "initial emergency request" and different from "existing emergency PDU session", the UE shall stop timer T3585 associated with the S-NSSAI of the PDU session, if it is running. If the timer value indicates neither zero nor deactivated and no S-NSSAI was provided during the PDU session establishment and the request type was different from "initial emergency request" and different from "existing emergency PDU session", the UE shall stop timer T3585 associated with no S-NSSAI if it is running. The timer T3585 to be stopped includes: 1) in a PLMN: i) the timer T3585 applied for all the PLMNs and for the access over which the PDU SESSION MODIFICATION REJECT is received, if running; ii) the timer T3585 applied for all the PLMNs and for both 3GPP access type and non-3GPP access type, if running; iii) the timer T3585 applied for the registered PLMN and for the access over which the PDU SESSION MODIFICATION REJECT is received, if running; and iv)- the timer T3585 applied for the registered PLMN and for both 3GPP access type and non-3GPP access type, if running; or 2) in an SNPN: i) the timer T3585 applied for all the equivalent SNPNs and for the access over which the PDU SESSION AUTHENTICATION COMMAND message is received, associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; ii) the timer T3585 applied for all the equivalent SNPNs and for both 3GPP access type and non-3GPP access type, associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; iii) the timer T3585 applied for the registered SNPN and for the access over which the PDU SESSION AUTHENTICATION COMMAND message is received, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and iv) the timer T3585 applied for the registered PLMN and for both 3GPP access type and non-3GPP access type, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. The UE shall then start timer T3585 with the value provided in the Back-off timer value IE or with the Back-off timer value received from the 5GMM sublayer and: 1) if an S-NSSAI was provided by the UE during the PDU session establishment, the UE shall not send another PDU SESSION ESTABLISHMENT REQUEST message with request type different from "initial emergency request" and different from "existing emergency PDU session", or another PDU SESSION MODIFICATION REQUEST message with exception of those identified in subclause 6.4.2.1, for a non-emergency PDU session for the S-NSSAI of the PDU session, until timer T3585 expires or timer T3585 is stopped; and 2) if the request type was different from "initial emergency request" and from "existing emergency PDU session", and an S-NSSAI was not provided by the UE during the PDU session establishment, the UE shall not send another PDU SESSION ESTABLISHMENT REQUEST message without an S-NSSAI and with request type different from "initial emergency request" and different from "existing emergency PDU session", or another PDU SESSION MODIFICATION REQUEST message with exception of those identified in subclause 6.4.2.1, for a non-emergency PDU session established without an S-NSSAI provided by the UE, until timer T3585 expires or timer T3585 is stopped. The UE shall not stop timer T3585 upon a PLMN change, SNPN change, or inter-system change; b) if the timer value indicates that this timer is deactivated and an S-NSSAI was provided during the PDU session establishment and the request type was different from "initial emergency request" and different from "existing emergency PDU session", the UE shall stop timer T3585 associated with the S-NSSAI of the PDU session, if it is running. If the timer value indicates that this timer is deactivated and no S-NSSAI was provided during the PDU session establishment and the request type was different from "initial emergency request" and different from "existing emergency PDU session", the UE shall stop timer T3585 associated with no S-NSSAI if it is running. The timer T3585 to be stopped includes: 1) in a PLMN: i) the timer T3585 applied for all the PLMNs and for the access over which the PDU SESSION MODIFICATION REJECT is received, if running; ii) the timer T3585 applied for all the PLMNs and for both 3GPP access type and non-3GPP access type, if running; iii) the timer T3585 applied for the registered PLMN and for the access over which the PDU SESSION MODIFICATION REJECT is received, if running; and iv) the timer T3585 applied for the registered PLMN and for both 3GPP access type and non-3GPP access type, if running; or 2) in an SNPN: i) the timer T3585 applied for all the equivalent SNPNs and for the access over which the PDU SESSION AUTHENTICATION COMMAND message is received, associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; ii) the timer T3585 applied for all the equivalent SNPNs and for both 3GPP access type and non-3GPP access type, associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; iii) the timer T3585 applied for the registered SNPN and for the access over which the PDU SESSION AUTHENTICATION COMMAND message is received, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and iv) the timer T3585 applied for the registered PLMN and for both 3GPP access type and non-3GPP access type, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. In addition: 1) if an S-NSSAI was provided by the UE during the PDU session establishment, the UE shall not send another PDU SESSION ESTABLISHMENT REQUEST message with request type different from "initial emergency request" and different from "existing emergency PDU session", or another PDU SESSION MODIFICATION REQUEST with exception of those identified in subclause 6.4.2.1, for a non-emergency PDU session for the S-NSSAI of the PDU session until the UE is switched off, the USIM is removed, the entry in the "list of subscriber data" for the current SNPN is updated, or the UE receives a PDU SESSION MODIFICATION COMMAND message for a non-emergency PDU session for the S-NSSAI of the PDU session from the network, or a PDU SESSION AUTHENTICATION COMMAND message for a non-emergency PDU session for the S-NSSAI of the PDU session from the network, or a PDU SESSION RELEASE COMMAND message without the Back-off timer value IE for the S-NSSAI of the PDU session from the network; and 2) if the request type was different from "initial emergency request" and from "existing emergency PDU session", and an S-NSSAI was not provided by the UE during the PDU session establishment, the UE shall not send another PDU SESSION ESTABLISHMENT REQUEST message without an S-NSSAI and with request type different from "initial emergency request" and different from "existing emergency PDU session", or another PDU SESSION MODIFICATION REQUEST message with exception of those identified in subclause 6.4.2.1, for a non-emergency PDU session established without an S-NSSAI provided by the UE, until the UE is switched off, the USIM is removed, the entry in the "list of subscriber data" for the current SNPN is updated, or the UE receives a PDU SESSION MODIFICATION COMMAND message for a non-emergency PDU session established without an S-NSSAI provided by the UE, or a PDU SESSION AUTHENTICATION COMMAND message for a non-emergency PDU session established without an S-NSSAI provided by the UE, or a PDU SESSION RELEASE COMMAND message without the Back-off timer value IE for a non-emergency PDU session established without an S-NSSAI provided by the UE. The timer T3585 remains deactivated upon a PLMN change, SNPN change, or inter-system change; and c) if the timer value indicates zero: 1) if an S-NSSAI was provided by the UE during the PDU session establishment, the UE shall stop timer T3585 associated with the S-NSSAI of the PDU session, if running. The timer T3585 to be stopped includes: i) in a PLMN: A) including the timer T3585 applied for all the PLMNs and for the access over which the PDU SESSION RELEASE COMMAND is received, if running; B) the timer T3585 applied for all the PLMNs and for the access over which the PDU SESSION RELEASE COMMAND is received, if running; C) the timer T3585 applied for the registered PLMN and for current access type or both 3GPP access type and non-3GPP access type, if running; and D) the timer T3585 applied for the registered PLMN and for both 3GPP access type and non-3GPP access type, if running; or ii) in an SNPN: A) the timer T3585 applied for all the equivalent SNPNs and for the access over which the PDU SESSION AUTHENTICATION COMMAND message is received, associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; B) the timer T3585 applied for all the equivalent SNPNs and for both 3GPP access type and non-3GPP access type, associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; C) the timer T3585 applied for the registered SNPN and for the access over which the PDU SESSION AUTHENTICATION COMMAND message is received, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and D) the timer T3585 applied for the registered PLMN and for both 3GPP access type and non-3GPP access type, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. The UE may send another PDU SESSION ESTABLISHMENT REQUEST message or PDU SESSION MODIFICATION REQUEST message for the S-NSSAI of the PDU session; and 2) if no S-NSSAI was provided during the PDU session establishment and the request type was different from “initial emergency request “ and different from “existing emergency PDU session”, the UE shall stop timer T3585 associated with no S-NSSAI The timer T3585 to be stopped includes: i) in a PLMN: A) the timer T3585 applied for all the PLMNs and for the access over which the PDU SESSION RELEASE COMMAND is received, if running; B) the timer T3585 applied for all the PLMNs and for the access over which the PDU SESSION RELEASE COMMAND is received, if running; C) the timer T3585 applied for the registered PLMN and for current access type or both 3GPP access type and non-3GPP access type, if running; and D) the timer T3585 applied for the registered PLMN and for both 3GPP access type and non-3GPP access type, if running; or ii) in an SNPN: A) the timer T3585 applied for all the equivalent SNPNs and for the access over which the PDU SESSION AUTHENTICATION COMMAND message is received, associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; B) the timer T3585 applied for all the equivalent SNPNs and for both 3GPP access type and non-3GPP access type, associated with the RSNPN or an equivalent SNPN and with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; C) the timer T3585 applied for the registered SNPN and for the access over which the PDU SESSION AUTHENTICATION COMMAND message is received, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running; and D) the timer T3585 applied for the registered PLMN and for both 3GPP access type and non-3GPP access type, associated with the RSNPN and, if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, associated with the selected entry of the "list of subscriber data" or the selected PLMN subscription, if running. The UE may send another PDU SESSION ESTABLISHMENT REQUEST message without an S-NSSAI, or another PDU SESSION MODIFICATION REQUEST message without an S-NSSAI provided by the UE. 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 SNPNs " is included in the PDU SESSION MODIFICATION REJECT message with the 5GSM cause value #69 "insufficient resources for specific slice", then the UE shall apply the timer T3585 for all the PLMNs or all the equivalent SNPNs. Otherwise, the UE shall apply the timer T3585 for the registered PLMN or the registered SNPN. If the Back-off timer value IE is not included or no Back-off timer value is received from the 5GMM sublayer, then the UE may send another PDU SESSION ESTABLISHMENT REQUEST message or PDU SESSION MODIFICATION REQUEST message for the same S-NSSAI or without an S-NSSAI. When the timer T3585 is running or the timer is deactivated, the UE is allowed to initiate a PDU session establishment procedure for emergency services. If the timer T3585 is running when the UE enters state 5GMM-DEREGISTERED, the UE remains switched on, and the USIM in the UE (if any) remains the same and the entry in the "list of subscriber data" for the SNPN to which timer T3585 is associated (if any) is not updated, then timer T3585 is kept running until it expires or it is stopped. If the UE is switched off when the timer T3585 is running, and if the USIM in the UE (if any) remains the same and the entry in the "list of subscriber data" for the SNPN to which timer T3585 is associated (if any) is not updated when the UE is switched on, the UE shall behave as follows: - let t1 be the time remaining for T3585 timeout at switch off and let t be the time elapsed between switch off and switch on. If t1 is greater than t, then the timer shall be restarted with the value t1 – t. If t1 is equal to or less than t, then the timer need not be restarted. If the UE is not capable of determining t, then the UE shall restart the timer with the value t1. If the UE is a UE operating in single-registration mode in a network supporting N26 interface and the PDU SESSION MODIFICATION REQUEST message was sent for a PDN connection established when in S1 mode after an inter-system change from S1 mode to N1 mode and timer T3585 associated with no S-NSSAI is running, then the UE shall re-initiate the UE-requested PDU session modification procedure after expiry of timer T3585. NOTE 3: As described in this subclause, upon PLMN change, SNPN change, or inter-system change, the UE does not stop the timer T3584 or T3585. This means the timer T3584 or T3585 can still be running or be deactivated for the given 5GSM procedure, the PLMN, the S-NSSAI and optionally the DNN combination when the UE returns to the PLMN or when it performs inter-system change back from S1 mode to N1 mode. Thus the UE can still be prevented from sending another PDU SESSION ESTABLISHMENT REQUEST or PDU SESSION MODIFICATION REQUEST message in the PLMN for the same S-NSSAI and optionally the same DNN. Upon PLMN change or SNPN change, if T3584 applied for the registered PLMN or the registered SNPN is running or is deactivated for an S-NSSAI, a DNN, and old PLMN or old SNPN, but T3584 is not running and is not deactivated for the S-NSSAI, the DNN, and new PLMN or new SNPN, then the UE is allowed to send a PDU SESSION ESTABLISHMENT REQUEST message for the same S-NSSAI and the same DNN in the new PLMN or new SNPN. Upon PLMN change or SNPN change, if T3585 applied for the registered PLMN or the registered SNPN is running or is deactivated for an S-NSSAI and old PLMN or old SNPN, but T3585 is not running and is not deactivated for the S-NSSAI and new PLMN or new SNPN, then the UE is allowed to send a PDU SESSION ESTABLISHMENT REQUEST message for the same S-NSSAI in the new PLMN or new SNPN. Upon SNPN change, if T3585 applied for all the equivalent SNPNs is running or is deactivated for an S-NSSAI and old SNPN, but T3585 is not running and is not deactivated for the S-NSSAI and new non-equivalent SNPN, then the UE is allowed to send a PDU SESSION ESTABLISHMENT REQUEST message for the same S-NSSAI in the new SNPN.