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Content for  TS 24.501  Word version:  17.5.0

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5.3.7  Handling of the periodic registration update timer and mobile reachable timerWord‑p. 156

The periodic registration update procedure is used over 3GPP access to periodically notify the availability of the UE to the network. The procedure is controlled in the UE by the periodic registration update timer, T3512.
If the UE is registered over the 3GPP access, the AMF maintains an implicit de-registration timer to control when the UE is considered implicitly de-registered over the 3GPP access. If the UE is registered over the non-3GPP access, the AMF also maintains a non-3GPP implicit de-registration timer to control when the UE is considered implicitly de-registered over the non-3GPP access. The UE registered over the non-3GPP access maintains a non-3GPP de-registration timer to control when the UE is considered implicitly de-registered for the non-3GPP access.
The AMF shall start a non-3GPP implicit de-registration timer for the UE registered over non-3GPP access when the N1 NAS signalling connection over non-3GPP access is released.
The UE registered over non-3GPP access shall reset and start a non-3GPP de-registration timer when the N1 NAS signalling connection over non-3GPP access is released. The non-3GPP de-registration timer is stopped when the UE enters 5GMM-CONNECTED mode over non-3GPP access or the 5GMM-DEREGISTERED state over non-3GPP access.
The non-3GPP implicit de-registration timer shall be longer than the non-3GPP de-registration timer.
The value of timer T3512 is sent by the network to the UE in the REGISTRATION ACCEPT message. The UE shall apply this value in all tracking areas of the list of tracking areas assigned to the UE until a new value is received. The periodic registration update timer only applies to the UE registered to the 5GS services over 3GPP access.
If timer T3512 received by the UE in a REGISTRATION ACCEPT message contains an indication that the timer is deactivated or the timer value is zero, then timer T3512 is deactivated and the UE shall not perform the periodic registration update procedure.
If during the registration procedure, the AMF does not indicate "strictly periodic registration timer supported" in the MICO indication IE to the UE, timer T3512 is reset and started with its initial value, when the UE changes from 5GMM-CONNECTED over 3GPP access to 5GMM-IDLE mode over 3GPP access. Timer T3512 is stopped when the UE enters 5GMM-CONNECTED mode over 3GPP access or the 5GMM-DEREGISTERED state over 3GPP access.
If during the registration procedure, the AMF indicates "strictly periodic registration timer supported" in the MICO indication IE to the UE, timer T3512 is started with its initial value after the completion of the registration procedure. The UE shall neither stop nor reset the timer T3512 when the UE enters 5GMM-CONNECTED or when changing from 5GMM-CONNECTED mode to 5GMM-IDLE mode. If the timer T3512 expires,
  1. the UE in 5GMM-CONNECTED mode over 3GPP access shall reset and start the timer T3512 with its initial value; or
  2. the UE in 5GMM-IDLE mode over 3GPP access shall perform the periodic registration procedure.
If the UE is registered for emergency services, and timer T3512 expires, the UE shall not initiate a periodic registration update procedure, but shall locally de-register from the network. When the UE is camping on a suitable cell, it may re-register to regain normal service.
When a UE is not registered for emergency services, and timer T3512 expires when the UE is in 5GMM-IDLE mode, the periodic registration update procedure shall be started.
If the UE is not registered for emergency services, and is in a state other than 5GMM-REGISTERED.NORMAL-SERVICE or 5GMM-REGISTERED.NON-ALLOWED-SERVICE over 3GPP access when timer T3512 expires, the periodic registration update procedure is delayed until the UE returns to 5GMM-REGISTERED.NORMAL-SERVICE or 5GMM-REGISTERED.NON-ALLOWED-SERVICE over 3GPP access.
The network supervises the periodic registration update procedure of the UE by means of the mobile reachable timer.
If the UE is not registered for emergency services, the mobile reachable timer shall be longer than the value of timer T3512. In this case, by default, the mobile reachable timer is 4 minutes greater than the value of timer T3512.
The network behaviour upon expiry of the mobile reachable timer is network dependent, but typically the network stops sending paging messages to the UE on the first expiry, and may take other appropriate actions.
If the UE is registered for emergency services, the AMF shall set the mobile reachable timer with a value equal to timer T3512. When the mobile reachable timer expires, the AMF shall locally de-register the UE.
The mobile reachable timer shall be reset and started with the value as indicated above, when the AMF releases the NAS signalling connection for the UE. The mobile reachable timer shall be stopped when a NAS signalling connection is established for the UE.
Upon expiry of the mobile reachable timer the network shall start the implicit de-registration timer over 3GPP access. The value of the implicit de-registration timer over 3GPP access is network dependent. If MICO mode is activated, the network shall start the implicit de-registration timer over 3GPP access when the UE enters 5GMM-IDLE mode at the AMF over 3GPP access. The default value of the implicit de-registration timer over 3GPP access is 4 minutes greater than the value of timer T3512.
If the implicit de-registration timer expires before the UE contacts the network, the network shall implicitly de-register the UE. The implicit de-registration timer shall be stopped when a NAS signalling connection is established for the UE.
If the non-3GPP implicit de-registration timer expires before the UE contacts the network over the non-3GPP access, the network shall implicitly de-register the UE and enter the state 5GMM-DEREGISTERED over non-3GPP access for the UE. The non-3GPP implicit de-registration timer shall be stopped when a NAS signalling connection over non-3GPP access is established for the UE.
If the non-3GPP de-registration timer expires before the UE contacts the network over the non-3GPP access, the UE shall enter the state 5GMM-DEREGISTERED over non-3GPP access. The non-3GPP de-registration timer shall be stopped when a NAS signalling connection over non-3GPP access is established for the UE.
If the AMF provides T3346 value IE in the DEREGISTRATION REQUEST message with Access type set to "Non-3GPP access" in Deregistration type IE, REGISTRATION REJECT message during a registration procedure for mobility and periodic registration update or SERVICE REJECT message and the value of timer T3346 is greater than the value of timer T3512, the AMF sets the mobile reachable timer and the implicit de-registration timer such that the sum of the timer values is greater than the value of timer T3346.
If the AMF provides T3346 value IE in the DEREGISTRATION REQUEST message with Access type set to "3GPP access" in Deregistration type IE, REGISTRATION REJECT message during a registration procedure for mobility and periodic registration update or SERVICE REJECT message and the value of timer T3346 is greater than the value of the non-3GPP de-registration timer, the AMF sets the non-3GPP implicit de-registration timer value to be 8 minutes greater than the value of timer T3346.
If the UE receives T3346 value IE in the DEREGISTRATION REQUEST message with Access type set to "3GPP access" in Deregistration type IE, REGISTRATION REJECT message during a registration procedure for mobility and periodic registration update or SERVICE REJECT message and the value of timer T3346 is greater than the value of the non-3GPP de-registration timer, the UE sets the non-3GPP de-registration timer value to be 4 minutes greater than the value of timer T3346.
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5.3.8  Handling of timer T3502Word‑p. 158

The value of timer T3502 can be sent by the network to the UE in the REGISTRATION ACCEPT message. The UE shall apply this value in all tracking areas of the registration area assigned to the UE, until a new value is received.
The value of timer T3502 can be sent by the network to the UE in the REGISTRATION REJECT message during the initial registration. If a REGISTRATION REJECT message including timer T3502 value was received integrity protected, the UE shall apply this value until a new value is received with integrity protection or a new PLMN is selected. Otherwise, the default value of this timer is used.
The default value of this timer is also used by the UE in the following cases:
  1. REGISTRATION ACCEPT message is received without a value specified;
  2. the UE does not have a stored value for this timer;
  3. a new PLMN which is not in the list of equivalent PLMNs has been entered, the initial registration procedure fails, the registration attempt counter is equal to 5 and no REGISTRATION REJECT message was received from the new PLMN;
  4. the network indicates that the timer is "deactivated"; or
  5. a new PLMN which is not in the list of equivalent PLMNs has been entered, the mobility and periodic update registration procedure fails and the registration attempt counter is equal to 5.
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5.3.9  Handling of NAS level mobility management congestion controlWord‑p. 158

The AMF may detect 5GMM signalling congestion and perform general NAS level congestion control. Under the 5GMM signalling congestion conditions the AMF may reject 5GMM signalling requests from UEs as specified in TS 23.501. The AMF should not reject the following:
  1. requests for emergency services;
  2. requests for emergency services fallback;
  3. requests from UEs configured for high priority access in selected PLMN;
  4. DEREGISTRATION REQUEST message;
  5. requests for mobile terminated services, triggered by paging or a notification procedure; and
  6. requests for initial registration or mobility and periodic registration update, when emergency is indicated by lower layers.
When general NAS level congestion control is active, the AMF may include a value for the mobility management back-off timer T3346 in the reject messages. The UE starts the timer T3346 with the value received in the 5GMM reject messages. To avoid that large numbers of UEs simultaneously initiate deferred requests, the AMF should select the value for the timer T3346 for the rejected UEs so that timeouts are not synchronised.
If the UE is registered in the same PLMN over the 3GPP access and non-3GPP access, and the UE receives the timer T3346 from the AMF, the timer T3346 shall apply to both 3GPP access and non-3GPP access.
If the UE receives the paging message or NOTIFICATION message when timer T3346 is running and the UE is registered to the same PLMN over 3GPP access and non-3GPP access, the UE shall stop the timer T3346 for both accesses and respond to the paging message or NOTIFICATION message as specified in subclause 5.6.2 and subclause 5.6.3.
If the timer T3346 is running when the UE enters state 5GMM-DEREGISTERED, the UE remains switched on, and the USIM in the UE remains the same, then the timer T3346 is kept running until it expires or it is stopped.
If the UE is switched off when the timer T3346 is running, the UE shall behave as follows when the UE is switched on and the USIM in the UE remains the same:
let t1 be the time remaining for T3346 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 enters a new PLMN while timer T3346 is running, and the new PLMN is not equivalent to the PLMN where the UE started timer T3346, the UE shall stop timer T3346 when initiating 5GMM procedures in the new PLMN.
After a change in registration area, if the timer T3346 is running and 5GS update status is 5U1 UPDATED then the UE shall set the 5GS update status to 5U2 NOT UPDATED and enter state 5GMM-REGISTERED.ATTEMPTING-REGISTRATION-UPDATE.
If timer T3346 is running or is deactivated, and the UE is a UE configured for high priority access in selected PLMN, or the UE needs to initiate signalling for emergency services or emergency services fallback, then the UE is allowed to initiate 5GMM procedures.
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5.3.10  Handling of DNN based congestion controlWord‑p. 159

The AMF may detect and start performing DNN based congestion control when one or more DNN congestion criteria as specified in TS 23.501 are met. If the UE does not provide a DNN for a non-emergency PDU session, then the AMF uses the selected DNN or the DNN associated with the PDU session corresponding to the 5GSM procedure.
When DNN based congestion control is activated at the AMF, the AMF performs the congestion control as specified in subclause 5.4.5 and the UE performs the congestion control as specified in subclause 5.4.5 and subclause 6.2.7.
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5.3.11  Handling of S-NSSAI based congestion controlWord‑p. 159

The AMF may detect and start performing S-NSSAI based congestion control when one or more S-NSSAI congestion criteria as specified in TS 23.501 are met. If the UE does not provide a DNN for a non-emergency PDU session, then the AMF uses the selected DNN or the DNN associated with the PDU session corresponding to the 5GSM procedure. If the UE does not provide an S-NSSAI for a non-emergency PDU session, then the AMF uses the selected S-NSSAI or the S-NSSAI associated with the PDU session corresponding to the 5GSM procedure.
When S-NSSAI based congestion control is activated at the AMF, the AMF performs the congestion control as specified in subclause 5.4.5 and the UE performs the congestion control as specified in subclause 5.4.5 and subclause 6.2.8.
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5.3.12  Handling of local emergency numbersWord‑p. 159

The additional requirements in subclause 5.3.12A apply to a UE supporting registration or attach procedures via 3GPP access and registration procedures via non-3GPP access.
In case of PLMN, the network may send a local emergency numbers list or an extended local emergency numbers list or both, in the REGISTRATION ACCEPT message, by including the Emergency number list IE and the Extended emergency number list IE, respectively. The Local emergency numbers list can be updated as described in TS 24.301, subclause 5.3.7.
In case of SNPN, the network may send an extended local emergency numbers list, in the REGISTRATION ACCEPT message, by including the Extended emergency number list IE. The network shall set the Extended Emergency Number List Validity (EENLV) field within the Extended emergency number list IE to "Extended Local Emergency Numbers List is valid only in the PLMN from which this IE is received". The UE shall consider the emergency number(s) received in the Extended emergency number list IE valid only in the SNPN from which this IE is received regardless of the received value of the EENLV field within the Extended emergency number list IE.
The UE shall store the local emergency numbers list and the extended local emergency numbers list, as provided by the network. The local emergency numbers list stored in the UE shall be replaced on each receipt of the Emergency number list IE. The extended local emergency numbers list stored in the UE shall be replaced on each receipt of the Extended emergency number list IE. The received local emergency numbers list or the received extended local emergency numbers list or both shall be provided to the upper layers.
If a REGISTRATION ACCEPT message is received via non-3GPP access from a PLMN in a country different from the current country of the UE, the UE shall keep the stored local emergency numbers list and the extended local emergency numbers list, if available.
The emergency number(s) received in the Emergency number list IE are valid only in PLMNs in the same country as the PLMN from which this IE is received. If no Emergency number list IE is contained in the REGISTRATION ACCEPT message, then the stored local emergency numbers list in the UE shall be kept, except if the UE has successfully registered to a PLMN in a country different from that of the PLMN that sent the list.
The emergency number(s) received in the Extended emergency number list IE are valid only in:
  • PLMNs in the same country as the PLMN from which this IE is received, if the Extended Emergency Number List Validity (EENLV) field within the Extended emergency number list IE indicates "Extended Local Emergency Numbers List is valid in the country of the PLMN from which this IE is received"; and
  • the PLMN from which this IE is received, if the EENLV field within the Extended emergency number list IE indicates "Extended Local Emergency Numbers List is valid only in the PLMN from which this IE is received"; and
  • the SNPN from which this IE is received, regardless of the value of the EENLV field within the Extended emergency number list IE.
If no Extended Local Emergency Numbers List is contained in the REGISTRATION ACCEPT message, and the registered PLMN or the registered SNPN has not changed, then the stored Extended Local Emergency Numbers List in the UE shall be kept. If no Extended Local Emergency Numbers List is contained in the REGISTRATION ACCEPT message, but the registered PLMN or the registered SNPN has changed, then:
  • if the last received indication in the EENLV field within the Extended emergency number list IE indicates "Extended Local Emergency Numbers List is valid only in the PLMN from which this IE is received", the stored Extended Local Emergency Numbers List in the UE shall be deleted; and
  • if the last received indication in the EENLV field within the Extended emergency number list IE indicates "Extended Local Emergency Numbers List is valid in the country of the PLMN from which this IE is received" the list shall be kept except if the UE has successfully registered to a PLMN in a country different from that of the PLMN that sent the stored list.
The local emergency numbers list and the extended local emergency numbers list shall be deleted at switch off or removal of the USIM. The UE shall be able to store up to ten entries in the local emergency numbers list and up to twenty entries in the Extended local emergency numbers list, received from the network.
For the use of the local emergency numbers list and the extended local emergency numbers list by the UE see TS 24.301, subclause 5.3.7.
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5.3.12A  Handling of local emergency numbers received via 3GPP access and non-3GPP accessWord‑p. 161

5.3.12A.1  GeneralWord‑p. 161

The requirements in subclause 5.3.12 with the clarifications and additional conditions in subclause 5.3.12A apply to a UE supporting:
  • attach procedures (see TS 24.301) or registration procedures via 3GPP access; and
  • registration procedures via non-3GPP access.
The UE shall ignore the presence or absence of local emergency numbers list, extended local emergency numbers list or both, in a REGISTRATION ACCEPT message received via non-3GPP access, unless conditions in subclause 5.3.12A.2 are met.
For the purposes of subclause 5.3.12A, the UE is considered neither registered nor attached over 3GPP access if:
  1. the UE supports 3GPP access to EPC, the UE does not support 3GPP access to 5GC, and:
    1. the EMM sublayer is in the EMM-NULL state, EMM-DEREGISTERED state or EMM-DEREGISTERED-INITIATED state; or
  2. the UE supports 3GPP access to 5GC, the UE does not support 3GPP access to EPC, and:
    1. the 5GMM sublayer is in the 5GMM-NULL state, 5GMM-DEREGISTERED state or 5GMM-DEREGISTERED-INITIATED state; or
  3. supports both 3GPP access to EPC and 3GPP access to 5GC, and:
    1. the EMM sublayer is in the EMM-NULL state, EMM-DEREGISTERED state or EMM-DEREGISTERED-INITIATED state; and
    2. the 5GMM sublayer is in the 5GMM-NULL state, 5GMM-DEREGISTERED state or 5GMM-DEREGISTERED-INITIATED state.
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5.3.12A.2  Receiving a REGISTRATION ACCEPT message via non-3GPP accessWord‑p. 161

If the UE can determine the current country and after switch on or after removal of the USIM, has not been registered or has not been attached via 3GPP access in the current country, then the UE shall store the local emergency numbers list or the extended local emergency numbers list or both, as provided by the network with an MCC matching the current country via non-3GPP access.
The UE shall replace a previously stored local emergency numbers list or a previously stored extended local emergency numbers list or both with a local emergency numbers list or an extended local emergency numbers list or both received in a REGISTRATION ACCEPT message via non-3GPP access, if the previously stored local emergency numbers list was also received via non-3GPP access or the previously stored extended local emergency numbers list was also received via non-3GPP access.
The UE shall replace a previously stored extended local emergency numbers list with an extended local emergency numbers list received in a REGISTRATION ACCEPT message via non-3GPP access, if:
  • the UE is neither registered nor attached over 3GPP access;
  • the REGISTRATION ACCEPT message is received from a PLMN different from which the stored list was received; and
  • the stored indication in the EENLV field within the Extended emergency number list IE indicates "Extended Local Emergency Numbers List is valid only in the PLMN from which this IE is received".
If no extended local emergency numbers list is contained in a REGISTRATION ACCEPT message received via non-3GPP access and the UE is neither registered nor attached over 3GPP access, the stored extended local emergency numbers list in the UE shall be discarded if:
  • the UE can determine the current country and the UE has successfully registered to a PLMN in the country and that country is different from that of the PLMN that sent the stored list via 3GPP access; or
  • the REGISTRATION ACCEPT message is received from a PLMN different from which the stored list was received, and the stored indication in the EENLV field within the Extended emergency number list IE indicates "Extended Local Emergency Numbers List is valid only in the PLMN from which this IE is received".
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5.3.13  Lists of 5GS forbidden tracking areasWord‑p. 162

If the UE is not operating in SNPN access operation mode, the UE shall store a list of "5GS forbidden tracking areas for roaming", as well as a list of "5GS forbidden tracking areas for regional provision of service". Otherwise the UE shall store a list of "5GS forbidden tracking areas for roaming":
  • per SNPN; and
  • if the UE supports access to an SNPN using credentials from a credentials holder, per entry of the "list of subscriber data" or PLMN subscription;
and store a list of "5GS forbidden tracking areas for regional provision of service":
  • per SNPN; and
  • if the UE supports access to an SNPN using credentials from a credentials holder, per entry of the "list of subscriber data" or PLMN subscription.
Within the 5GS, these lists are managed independently per access type, i.e., 3GPP access or non-3GPP access. These lists shall be erased when:
a) the UE is switched off, the UICC containing the USIM is removed, an entry of the "list of subscriber data" with the subscribed SNPN identity identifying the current SNPN is updated or, if the UE supports access to an SNPN using credentials from a credentials holder, the entry of the "list of subscriber data" associated with the lists is updated; and
b) periodically (with a period in the range 12 to 24 hours).
Over 3GPP access, when the lists are erased, the UE performs cell selection according to TS 38.304 or TS 36.304. A tracking area shall be removed from the list of "5GS forbidden tracking areas for roaming", as well as the list of "5GS forbidden tracking areas for regional provision of service", if the UE receives the tracking area in the TAI list or the Service area list of "allowed tracking areas" in REGISTRATION ACCEPT message or a CONFIGURATION UPDATE COMMAND message. The UE shall not remove the tracking area from "5GS forbidden tracking areas for roaming" or "5GS forbidden tracking areas for regional provision of service" if the UE is registered for emergency services.
In N1 mode, the UE shall update the suitable list whenever a REGISTRATION REJECT, SERVICE REJECT or DEREGISTRATION REQUEST message is received with the 5GMM cause #12 "tracking area not allowed", #13 "roaming not allowed in this tracking area", or #15 "no suitable cells in tracking area".
Each list shall accommodate 40 or more TAIs. When the list is full and a new entry has to be inserted, the oldest entry shall be deleted.
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5.3.13A  Forbidden PLMN lists |R16|Word‑p. 162

In N1 mode, two lists of forbidden PLMN are managed independently per access type, i.e., 3GPP access or non-3GPP access:
  • the list of "forbidden PLMNs" as defined in TS 23.122 is applicable for 3GPP access in N1 mode. The same list is used by 5GMM for 3GPP access, EMM, GMM and MM (see TS 24.301 and TS 24.008), regardless whether the UE is operating in single-registration mode or dual-registration mode.
  • the list of "forbidden PLMNs for non-3GPP access to 5GCN" as defined in TS 24.502 is applicable for 5GMM for non-3GPP access.
The list of "forbidden PLMNs for GPRS service" as defined in TS 23.122 and TS 24.008 is applicable for 3GPP access in N1 mode. The same list is used by 5GMM for 3GPP access, EMM and GMM (see TS 24.301 and TS 24.008), regardless whether the UE is operating in single-registration mode or dual-registration mode.
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5.3.14  List of equivalent PLMNsWord‑p. 163

The UE shall store a list of equivalent PLMNs. These PLMNs shall be regarded by the UE as equivalent to each other for PLMN selection and cell selection/re-selection. The same list is used by 5GMM, EMM, GMM and MM (see TS 24.301 and TS 24.008) except for the case when the UE operates in dual-registration mode (see subclause 4.8.3).
The UE shall update or delete this list at the end of each registration procedure. The stored list consists of a list of equivalent PLMNs as downloaded by the network plus the PLMN code of the registered PLMN that downloaded the list. When the UE is switched off, the UE shall keep the stored list so that it can be used for PLMN selection after switch on. The UE shall delete the stored list if the USIM is removed or when the UE registered for emergency services enters the state 5GMM-DEREGISTERED. The maximum number of possible entries in the stored list is 16.
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5.3.15  Transmission failure abnormal case in the UEWord‑p. 163

The abnormal case 5GMM uplink message transmission failure indication by lower layers can be identified for 5GMM procedures:
When it is specified in the relevant procedure that it is up to the UE implementation to re-run the ongoing procedure that triggered that procedure, the procedure can typically be re-initiated using a retransmission mechanism of the uplink message (i.e. the one that has previously failed to be transmitted) with new sequence number and message authentication code information thus avoiding to re-start the whole procedure.
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5.3.16  Extended DRX cycle for UEs in 5GMM-IDLE |R16|Word‑p. 163

Extended DRX (eDRX) cycle is supported for a UE in N1 mode. When eDRX is requested by the UE and accepted by the network:
  • if the UE is not in NB-N1 mode, eDRX is used when the UE is in 5GMM-IDLE mode or in 5GMM-CONNECTED mode with RRC inactive indication; or
  • if the UE is in NB-N1 mode, eDRX is used when the UE is in 5GMM-IDLE mode.
The UE may request the use of eDRX cycle during a registration procedure by including the Requested extended DRX parameters IE (see TS 23.501 and TS 23.502). The UE shall not request the use of eDRX during a registration procedure for emergency services.
The UE and the network may negotiate eDRX parameters during a registration procedure when the UE has an emergency PDU session.
The network accepts the request to use the eDRX by providing the Negotiated extended DRX parameters IE when accepting the registration procedure. The UE shall use eDRX only if it received the Negotiated extended DRX parameters IE during the last registration procedure and the UE does not have an emergency PDU session.
If the UE received the Negotiated extended DRX parameters IE during the last registration procedure, upon successful completion of the PDU session release procedure of the emergency PDU session, the UE shall resume eDRX.
If the network has provided the Negotiated extended DRX parameters IE during the last registration procedure, upon successful completion of the PDU session release procedure of the emergency PDU session, the network shall resume eDRX.
If the UE or the network locally releases an emergency PDU session, the UE or the network shall not use eDRX until the UE receives eDRX parameters during a registration procedure with PDU session context synchronization or upon successful completion of a service request procedure with PDU session context synchronization.
If the UE did not receive the Negotiated extended DRX parameters IE, or if the UE has an emergency PDU session, the UE shall use the stored UE specific DRX parameter, if available.
If the network did not accept the request to use eDRX, or if the UE has an emergency PDU session, the network shall use the stored UE specific DRX parameter, if available.
If the network provided the Negotiated extended DRX parameters IE which was different from the one requested by the UE and also assigned a new 5G-GUTI for the UE as described in subclause 5.5.1.3.4 during the last registration procedure, the network shall use the stored UE specific DRX parameter, if available, with the old 5G-GUTI and use the eDRX provided by the network with the new 5G-GUTI until the old 5G-GUTI can be considered as invalid by the network (see subclause 5.4.4.4 and subclause 5.5.1.3.4).
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5.3.17  Service Gap Control |R16|Word‑p. 164

Service gap control (SGC) only applies to 3GPP access.
The network may control the frequency with which UEs can transition from 5GMM-IDLE mode to 5GMM-CONNECTED mode via the SGC as specified in TS 23.501 and TS 23.502. If the network supports SGC and the service gap time value i.e. T3447 value is available in the 5GMM context of the UE, the AMF shall consider SGC as active for the UE.
The UE and the network negotiate usage of SGC during the registration procedure for initial registration and registration procedure for mobility and periodic registration update:
  • the UE supporting SGC indicates its support in the REGISTRATION REQUEST message. If the UE supports SGC and the SGC is active for the UE, the AMF includes T3447 value IE in the REGISTRATION ACCEPT message (see subclause 5.5.1.2 and subclause 5.5.1.3). The UE stores the T3447 value; and
  • for UEs that do not support SGC when the network rejects mobility management signalling requests because SGC is active in the network, the mechanism for general NAS level mobility management congestion control as specified in subclause 5.3.9 applies.
The network can provide a new T3447 value to the UE to be used next time it is started or stop timer T3447 in the UE if running with the Generic UE configuration update procedure as specified in subclause 5.4.4.
The UE shall start timer T3447 when the N1 NAS signalling connection is released and if:
  • the UE supports SGC, and the T3447 value is available in the UE and does not indicate zero; and
  • the N1 NAS signalling connection released was not established for:
    • paging;
    • registration procedure for initial registration with Follow-on request indicator set to "No follow-on request pending";
    • registration procedure for mobility and periodic registration update with Follow-on request indicator set to "No follow-on request pending" and without Uplink data status IE included;
    • requests for emergency services; or
    • requests for exception data reporting.
If the SGC is active in the network, after the UE transitions from 5GMM-CONNECTED mode to 5GMM-IDLE mode except when the UE was in 5GMM-CONNECTED mode due to:
  • paging;
  • registration procedure for initial registration with Follow-on request indicator set to "No follow-on request pending";
  • registration procedure for mobility and periodic registration update with Follow-on request indicator set to "No follow-on request pending" and without Uplink data status IE included,
  • requests for emergency services; or
  • requests for exception data reporting,
the network shall start timer T3447 if not already running:
  • with the T3447 value available in the 5GMM context minus 4 minutes, if the UE supports SGC and the T3447 value has been sent to the UE with a non-zero value; or
  • with the T3447 value available in the 5GMM context if the UE does not support SGC.
When timer T3447 is running, the network allows:
  • requests for emergency service;
  • requests for emergency services fallback;
  • requests for high priority access;
  • requests for exception data reporting;
  • registration procedure for initial registration with Follow-on request indicator set to "No follow-on request pending";
  • registration procedure for mobility and periodic registration update without Uplink data status IE included and with Follow-on request indicator set to "No follow-on request pending"; or
  • service request procedure or registration procedure for mobility and periodic registration update triggered by paging and subsequent MO signalling or MO data, if any, until the UE enters 5GMM-IDLE mode.
The UE or the network with a running T3447 timer keeps the timer running when the UE transits from 5GMM-IDLE mode to 5GMM-CONNECTED mode.
If timer T3447 is running when the UE changes PLMN or enters state 5GMM-DEREGISTERED, the UE remains switched on, and the USIM in the UE remains the same, then timer T3447 is kept running until it expires.
If the AMF determines that the UE operating in single-registration mode has performed an inter-system change from N1 mode to S1 mode and the timer T3447 is running in the AMF, the AMF stops the T3447.
Upon inter-system change from S1 mode to N1 mode, if the UE supports service gap control, T3447 is running in the UE, and the T3447 value IE is included in the REGISTRATION ACCEPT message received from the AMF (see subclause 5.5.1.2 and subclause 5.5.1.3), the UE shall keep T3447 running. Additionally, the UE shall store and replace the currently stored service gap time value with the received T3447 value. Upon expiry of the running T3447 timer, the UE shall use the new value when starting T3447 again.
If the UE is switched off when the timer T3447 is running, the UE shall behave as follows when the UE is switched on and the USIM in the UE remains the same:
  • let t1 be the time remaining for timer T3447 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.
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5.3.18  Restriction on use of enhanced coverage |R16|Word‑p. 166

In order to deal with use of extensive resources from the network, the operator may prevent specific subscribers from using enhanced coverage (see TS 23.501). When in NB-N1 mode, the UE shall indicate support for restriction on use of enhanced coverage. When in WB-N1 mode, the UE supporting either CE mode A or CE mode B shall indicate support for restriction on use of enhanced coverage. The UE supporting restriction on use of enhanced coverage indicates its support for restriction on use of enhanced coverage in the REGISTRATION REQUEST message. If the UE supports restriction on use of enhanced coverage, the AMF indicates in the REGISTRATION ACCEPT message (see subclause 5.5.1.2 and subclause 5.5.1.3) that:
  1. when in WB-N1 mode, whether CE mode B is restricted for the UE, or both CE mode A and CE mode B are restricted for the UE, or both CE mode A and CE mode B are not restricted for the UE; or
  2. when in NB-N1 mode, whether the use of enhanced coverage is restricted or not for the UE.
If:
  1. the use of enhanced coverage is restricted;
  2. the use of CE mode B is restricted; or
  3. the use of CE mode A and CE mode B is restricted,
the UE shall not use enhanced coverage in the registered PLMN and in any PLMN which is in the list of equivalent PLMNs.
If the UE supports CE mode B and the network determines that
  1. the use of enhanced coverage is not restricted for the UE; or
  2. CE mode B is not restricted for the UE,
the applicable NAS timer values shall be calculated by the network as described in subclause 4.19 and subclause 4.20.
For a UE that supports restriction on use of enhanced coverage or CE mode B, if:
  1. the AMF determines to enforce a change in restriction on the use of enhanced coverage or a change in the restriction on the use of CE mode B as described in TS 23.501; and
  2. the UE is in 5GMM-CONNECTED mode and there is no ongoing registration procedure,
the AMF shall initiate the generic UE configuration update procedure to indicate registration requested and release of the N1 NAS signalling connection not requested as described in subclause 5.4.4. After the successful completion of the registration procedure for mobility registration update including change of the restriction on the use of enhanced coverage, for any SMF with which the UE has an established PDU session, the AMF updates the SMF with the indication on the use of extended NAS timer setting as described in TS 23.501 and TS 23.502.
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