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Content for  TS 24.501  Word version:  18.0.1

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5.3  General on elementary 5GMM proceduresp. 147

5.3.1  5GMM modes and N1 NAS signalling connectionp. 147

5.3.1.1  Establishment of the N1 NAS signalling connectionp. 147

When the UE is in 5GMM-IDLE mode over 3GPP access and needs to transmit an initial NAS message, the UE shall request the lower layer to establish an RRC connection. Upon indication from the lower layers that the RRC connection has been established, the UE shall consider that the N1 NAS signalling connection over 3GPP access is established and enter 5GMM-CONNECTED mode over 3GPP access.
When the UE is in 5GMM-IDLE mode over non-3GPP access, and the UE receives an indication from the lower layers of non-3GPP access, that the access stratum connection is established between the UE and the network, the UE shall send an initial NAS message, consider the N1 NAS signalling connection is established and enter 5GMM-CONNECTED mode over non-3GPP access.
Initial NAS messages are:
  1. REGISTRATION REQUEST message;
  2. DEREGISTRATION REQUEST message;
  3. SERVICE REQUEST message; and
  4. CONTROL PLANE SERVICE REQUEST.
If the UE is capable of both N1 mode and S1 mode and lower layers provide an indication that the current E-UTRA cell is connected to both EPC and 5GCN, for the routing of the REGISTRATION REQUEST message during the initial registration procedure to the appropriate core network (EPC or 5GCN), the UE NAS provides the lower layers with the selected core network type information.
For the routing of the initial NAS message to the appropriate AMF, if the UE holds a 5G-GUTI or 4G-GUTI, the UE NAS provides the lower layers with the UE identity according to the following rules:
  1. if the registration procedure for mobility and periodic update was triggered due to the last CONFIGURATION UPDATE COMMAND message containing the Configuration update indication IE with the Registration bit set to "registration requested" and including:
    1. no other parameters;
    2. one or both of the Allowed NSSAI IE and the Configured NSSAI IE; or
    3. the Network slicing indication IE with the Network slicing subscription change indication set to "Network slicing subscription changed";
    the UE NAS shall not provide the lower layers with the 5G-S-TMSI or the registered GUAMI;
  2. if the service request procedure was initiated over non-3GPP access, the UE NAS shall provide the lower layers with the registered GUAMI, but shall not provide the lower layers with the 5G-S-TMSI;
  3. if the initial NAS message other than the SERVICE REQUEST or CONTROL PLANE SERVICE REQUEST message was initiated over untrusted non-3GPP access, the UE NAS shall provide the lower layers with the GUAMI of the 5G-GUTI that the UE NAS has selected as specified in the subclause 5.5.1.2.2 and 5.5.1.3.2, but shall not provide the lower layers with the 5G-S-TMSI;
    if the initial NAS message other than the SERVICE REQUEST or CONTROL PLANE SERVICE REQUEST message was initiated over trusted non-3GPP access, the UE NAS shall provide the lower layers with the 5G-GUTI, if available, otherwise shall provide the lower layers with the SUCI;
    if the UE is the 5G-RG and the initial NAS message other than the SERVICE REQUEST or CONTROL PLANE SERVICE REQUEST message was initiated over wireline access, the UE NAS shall provide the lower layers with the GUAMI of the 5G-GUTI that the UE NAS has selected as specified in the subclause 5.5.1.2.2 and 5.5.1.3.2, if available, otherwise shall not provide the lower layers with any UE identity;
  4. if the UE does not hold a 5G-GUTI that was previously assigned by the same PLMN with which the UE is performing the registration procedure and if:
    1. the UE operating in the single-registration mode performs a registration procedure for mobility and periodic update indicating "mobility registration updating" following an inter-system change from S1 mode to N1 mode; or
    2. the UE which was previously registered in S1 mode before entering state EMM-DEREGISTERED, performs an initial registration procedure, the UE has received the interworking without N26 interface indicator set to "interworking without N26 interface not supported" from the network, and the UE holds a 4G-GUTI;
    then the UE NAS provides the lower layers with a GUAMI part of the 5G-GUTI mapped from 4G-GUTI as specified in TS 23.003 with an indication that the GUAMI is mapped from EPS; or
  5. otherwise:
    1. if the tracking area of the current cell is in the registration area, the UE NAS shall provide the lower layers with the 5G-S-TMSI, but shall not provide the registered GUAMI to the lower layers; or
    2. if the tracking area of the current cell is not in the registration area, the UE NAS shall provide the lower layers with the GUAMI of the 5G-GUTI that the UE NAS has selected as specified in the subclauses 5.5.1.2.2 and 5.5.1.3.2, but shall not provide the lower layers with the 5G-S-TMSI.
For 3GPP access and untrusted non-3GPP access, if the UE does not hold a 5G-GUTI and the UE does not hold a 4G-GUTI, the UE NAS does not provide the lower layers with the 5G-S-TMSI or the registered GUAMI. For trusted non-3GPP access, if the UE does not hold a 5G-GUTI and the UE does not hold a 4G-GUTI, the UE NAS provides the lower layers with the SUCI.
The UE NAS also provides the lower layers with the identity of the selected PLMN (see TS 38.331) if the UE is not operating in SNPN access operation mode. If the UE is operating in SNPN access operation mode, the UE NAS provides the lower layers with the SNPN identity of the selected SNPN. In a shared network, the UE shall choose one of the PLMN identity(ies) or SNPN identity(ies) as specified in TS 23.122.
The UE NAS layer may provide the lower layers with an NSSAI as specified in subclause 4.6.2.3.
If the UE performs initial registration for onboarding services in SNPN or is registered for onboarding services in SNPN, the UE NAS layer shall provide the lower layers with an indication that the connection is for onboarding.
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5.3.1.2  Re-establishment of the N1 NAS signalling connectionp. 149

When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has no pending NAS procedure and no pending uplink user data for PDU session(s) with user-plane resources already established, the UE shall:
  1. enter 5GMM-IDLE mode; and
  2. initiate the registration procedure for mobility and periodic registration update and include the Uplink data status IE in the REGISTRATION REQUEST message indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclause 5.5.1.3 for further details).
When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has pending uplink user data for PDU session(s) with user-plane resources already established but no pending NAS procedure, the UE shall:
  1. enter 5GMM-IDLE mode; and
  2. initiate the service request procedure and include the Uplink data status IE in the SERVICE REQUEST message indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication (see subclause 5.6.1 for further details).
When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has a pending registration procedure, a service request procedure, or a de-registration procedure, the UE shall:
  1. enter 5GMM-IDLE mode;
  2. proceed with the pending procedure; and
  3. if the pending procedure is a service request or registration procedure and the SERVICE REQUEST message, the CONTROL PLANE SERVICE REQUEST message or the REGISTRATION REQUEST message does not include UE request type IE with Request type value set to "NAS signalling connection release", the UE shall include the Uplink data status IE in the SERVICE REQUEST message, or in the REGISTRATION REQUEST message, indicating the PDU session(s) for which user-plane resources were not active prior to receiving a fallback indication from the lower layers and the UE has pending user data to be sent over 3GPP access, if any, and the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclauses 5.5.1.3 and 5.6.1 for further details).
When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has a pending NAS procedure other than a registration procedure, a service request procedure, or a de-registration procedure, the UE shall:
  1. enter 5GMM-IDLE mode;
  2. initiate the service request procedure and include the Uplink data status IE in the SERVICE REQUEST message indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclause 5.6.1 for further details); and
  3. upon successful service request procedure completion, proceed with any pending procedure.
When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has no pending NAS procedure and no pending uplink user data for PDU session(s) with user-plane resources already established, and the UE was using network resources for 5G ProSe direct discovery over PC5 or 5G ProSe direct communication over PC5 (see TS 23.304), the UE shall:
  1. enter 5GMM-IDLE mode; and
  2. initiate the service request procedure and include the Uplink data status IE in the SERVICE REQUEST message indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclause 5.6.1 for further details).
The cases above apply when the UE is in an allowed area or when the UE is not in a non-allowed area.
When the UE:
  1. is in a non-allowed area or is not in an allowed area;
  2. is in 5GMM-CONNECTED mode over 3GPP access;
  3. receives a fallback indication from lower layers; and
  4. does not have signalling pending,
the UE shall:
  1. enter 5GMM-IDLE mode; and
  2. initiate the registration procedure for mobility and periodic registration update. The UE shall not include the Uplink data status IE in the REGISTRATION REQUEST message except if the PDU session for which user-plane resources were active is an emergency PDU session, or if the UE is configured for high priority access in the selected PLMN.
In the above cases when the UE receives a fallback indication from lower layers, if the UE is in non-allowed area or not in allowed area, the UE shall behave as specified in subclause 5.3.5.
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5.3.1.3  Release of the N1 NAS signalling connectionp. 150

The signalling procedure for the release of the N1 NAS signalling connection is initiated by the network.
In N1 mode, upon indication from lower layers that the access stratum connection has been released, the UE shall enter 5GMM-IDLE mode and consider the N1 NAS signalling connection released.
If the UE in 3GPP access is configured for eCall only mode as specified in TS 31.102 then:
  • if the N1 NAS signalling connection that was released had been established for eCall over IMS, the UE shall start timer T3444; and
  • if the N1 NAS signalling connection that was released had been established for a call to an HPLMN designated non-emergency MSISDN or URI for test or terminal reconfiguration service, the UE shall start timer T3445.
The UE shall start the timer T3447 if not already running when the N1 NAS signalling connection is released as specified in subclause 5.3.17.
To allow the network to release the N1 NAS signalling connection, the UE:
  1. shall start the timer T3540 if the UE receives any of the 5GMM cause values #7, #11, #12, #13, #15, #27, #31, #62, #72, #73, #74, #75, #76 and the UE does not consider the received 5GMM cause value as abnormal case as specified in subclauses 5.5.1.2.7, 5.5.1.3.7 and 5.5.2.3.4;
  2. shall start the timer T3540 for a UE in 3GPP access if:
    1. the UE receives a REGISTRATION ACCEPT message which does not include a Pending NSSAI IE or UE radio capability ID deletion indication IE;
    2. the UE has set the Follow-on request indicator to "No follow-on request pending" in the REGISTRATION REQUEST message;
    3. the UE has not included the Uplink data status IE in the REGISTRATION REQUEST message, or the UE has included the Uplink data status IE in the REGISTRATION REQUEST message but the REGISTRATION ACCEPT message indicates that no user-plane resources of any PDU sessions are to be re-established;
    4. the UE has not included the Allowed PDU session status IE or has included the Allowed PDU session status IE indicating there is no PDU session(s) for which the UE allowed the user-plane resource to be re-established over 3GPP access in the REGISTRATION REQUEST message, or the UE has included the Allowed PDU session status IE in the REGISTRATION REQUEST message but the REGISTRATION ACCEPT message does not indicate that any user-plane resources of any PDU sessions are to be re-established;
    5. the registration procedure has been initiated in 5GMM-IDLE mode, or the UE has set Request type to "NAS signalling connection release" in the UE request type IE in the REGISTRATION REQUEST message and the N1 NAS signalling connection release bit is set to "N1 NAS signalling connection release supported" in the 5GS network feature support IE of the REGISTRATION ACCEPT message;
    6. the user-plane resources for PDU sessions have not been set up, except for the case the UE has set Request type to "NAS signalling connection release" in the UE request type IE in the REGISTRATION REQUEST message and the N1 NAS signalling connection release bit is set to "N1 NAS signalling connection release supported" in the 5GS network feature support IE of the REGISTRATION ACCEPT message;
    7. the UE need not request resources for V2X communication over PC5 reference point (see TS 23.287); and
    8. the UE need not request resources for 5G ProSe direct discovery over PC5 or 5G ProSe direct communication over PC5 (see TS 23.304);
  3. shall start the timer T3540 if the UE receives a REGISTRATION REJECT message indicating:
    the 5GMM cause value #9 or #10;
  4. shall start the timer T3540 if the UE receives a SERVICE REJECT message indicating:
    the 5GMM cause value #9, #10; or
    the 5GMM cause value #28 and with no emergency PDU session has been established;
  5. shall start the timer T3540 if:
    1. the UE receives a CONFIGURATION UPDATE COMMAND message containing the Configuration update indication IE with the Registration bit set to "registration requested" and with:
      1. either new allowed NSSAI information or new configured NSSAI information or both included;
      2. the network slicing subscription change indication; or
      3. no other parameters;
    2. the user-plane resources for PDU sessions have not been set up; and
  6. shall start the timer T3540 for a UE in 3GPP access if:
    1. the UE receives a SERVICE ACCEPT message;
    2. for the case that the UE sent the:
      1. SERVICE REQUEST message, the UE did not set the Service type IE to "signalling" or "high priority access", the UE has not included the Uplink data status IE in the SERVICE REQUEST message, or the UE has included the Uplink data status IE in the SERVICE REQUEST message but the SERVICE ACCEPT message indicates that no user-plane resources of any PDU sessions are to be re-established; or
      2. CONTROL PLANE SERVICE REQUEST message, the UE did not set the Control plane service type IE to "emergency services fallback", the UE has not included the Uplink data status IE in the CONTROL PLANE SERVICE REQUEST message, or the UE has included the Uplink data status IE in the CONTROL PLANE SERVICE REQUEST message but the SERVICE ACCEPT message indicates that no user-plane resources of any PDU sessions are to be re-established;
    3. the UE has not included the Allowed PDU session status IE or has included the Allowed PDU session status IE indicating there is no PDU session(s) for which the UE allowed the user-plane resource to be re-established over 3GPP access in the SERVICE REQUEST message or the CONTROL PLANE SERVICE REQUEST message, or the UE has included the Allowed PDU session status IE in the SERVICE REQUEST message or the CONTROL PLANE SERVICE REQUEST message but the SERVICE ACCEPT message does not indicate that any user-plane resources of any PDU sessions are to be re-established;
    4. the service request procedure has been initiated in 5GMM-IDLE mode;
    5. the user-plane resources for PDU sessions have not been set up;
    6. the UE need not request resources for V2X communication over PC5 reference point (see TS 23.287); and
    7. the UE need not request resources for 5G ProSe direct discovery over PC5 or 5G ProSe direct communication over PC5 (see TS 23.304);
  7. may start the timer T3540 if the UE receives any of the 5GMM cause values #3 or #6 or if it receives an AUTHENTICATION REJECT message;
  8. shall start the timer T3540 upon completion of the configuration update procedure or the registration procedure if the UE does not have an emergency PDU session and:
    1. the UE received a CONFIGURATION UPDATE COMMAND message or a REGISTRATION ACCEPT message while camping on a CAG cell and the entry for the current PLMN in the received "CAG information list" does not include any of the CAG-ID(s) supported by the current CAG cell;
    2. the UE received a CONFIGURATION UPDATE COMMAND message or a REGISTRATION ACCEPT message while camping on a non-CAG cell and the entry for the current PLMN in the received "CAG information list" includes an "indication that the UE is only allowed to access 5GS via CAG cells"; or
    3. the UE received a CONFIGURATION UPDATE COMMAND message while camping on a CAG cell and the entry for the current PLMN in not included in the received "CAG information list"; or
  9. shall start the timer T3540 for a UE in 3GPP access if:
    1. the UE receives a SERVICE ACCEPT message; and
    2. the UE:
      • has set Request type to "NAS signalling connection release" in the UE request type IE in the SERVICE REQUEST message or CONTROL PLANE SERVICE REQUEST message; or
      • has set Request type to "Rejection of paging" in the UE request type IE in the SERVICE REQUEST message or CONTROL PLANE SERVICE REQUEST message and the UE receives a CONFIGURATION UPDATE COMMAND message
  10. shall start the timer T3540 if the UE receives the 5GMM cause value #22 along with a T3346 value, and the value indicates that the timer T3346 is neither zero nor deactivated and the NAS procedure has been initiated in 5GMM-IDLE mode; or
  11. shall start the timer T3540 if the UE receives a DEREGISTRATION ACCEPT message.
Upon expiry of T3540,
  • in cases a), b), f), g), h), i), j) and k) the UE shall locally release the established N1 NAS signalling connection;
  • in cases c) and d) the UE shall locally release the established N1 NAS signalling connection and the UE shall initiate the registration procedure as described in subclause 5.5.1.3 or 5.6.1.5; or
  • in case e), the UE shall locally release the established N1 NAS signalling connection and perform a new registration procedure as specified in subclause 5.5.1.3.2.
In case a),
  • upon receiving a request from the upper layers to perform emergency services fallback only for a UE in 3GPP access or establishing an emergency PDU session, the UE shall stop timer T3540 and shall locally release the N1 NAS signalling connection, before proceeding as specified in subclause 5.5.1.
In case b) and f),
  • upon an indication from the lower layers that the user-plane resources for PDU sessions are set up, the UE shall stop timer T3540 and may send uplink signalling via the existing N1 NAS signalling connection or user data via user plane. If the uplink signalling is associated with emergency services fallback only for a UE in 3GPP access or establishing an emergency PDU session, the UE shall stop timer T3540 and send the uplink signalling via the existing N1 NAS signalling connection;
In case b), f) and i),
  • upon receipt of a DEREGISTRATION REQUEST message, the UE shall stop timer T3540 and respond to the network-initiated de-registration request via the existing N1 NAS signalling connection as specified in subclause 5.5.2.3;
  • upon receipt of a message of a network-initiated 5GMM common procedure except a CONFIGURATION UPDATE COMMAND message without requesting acknowledgement, the UE shall stop timer T3540 and respond to the network-initiated 5GMM common procedure via the existing N1 NAS signalling connection as specified in subclause 5.4;
  • if there is no user-plane resources established for PDU sessions, upon receiving a request from the upper layers to perform emergency services fallback only for a UE in 3GPP access or establishing an emergency PDU session, the UE shall stop timer T3540 and shall locally release the N1 NAS signalling connection, before proceeding as specified in subclause 5.6.1;
  • if there is no user-plane resources established for PDU sessions, upon receiving a request from the upper layers to perform services other than emergency services fallback only for a UE in 3GPP access or establishing an emergency PDU session, the UE shall wait for the local release of the established N1 NAS signalling connection upon expiry of timer T3540 or wait for timer T3540 being stopped, before initiating NAS signalling;
  • upon receipt of a DL NAS TRANSPORT message, the UE shall stop timer T3540 and may send uplink signalling via the existing N1 NAS signalling connection; or
  • upon initiation of registration procedure for mobility and periodic registration update as specified in subclause 5.5.1.2.7 for cases h), i), j), subclause 5.5.1.3.7 for cases j), k) or subclause 5.5.1.3.2 for case a), the UE shall stop timer T3540.
In case c) and d),
  • upon an indication from the lower layers that the access stratum connection has been released, the UE shall stop timer T3540 and perform a new registration procedure as specified in subclause 5.5.1.3.5 or 5.6.1.5.
  • upon receiving a request from the upper layers to perform emergency services fallback only for a UE in 3GPP access or establishing an emergency PDU session, the UE shall stop timer T3540 and shall locally release the N1 NAS signalling connection, before proceeding as specified in subclause 5.5.1.
In case e),
  • upon an indication from the lower layers that the access stratum connection has been released, the UE shall stop timer T3540 and perform a new registration procedure as specified in subclause 5.5.1.3.2.
  • upon an indication from the lower layers that the user-plane resources for PDU sessions are set up, the UE shall stop timer T3540 and may send user data via user plane.
  • upon receiving a request from the upper layers to perform emergency services fallback only for a UE in 3GPP access or establishing an emergency PDU session, the UE shall stop timer T3540 and shall locally release the N1 NAS signalling connection, before proceeding as specified in subclause 5.5.1.
If the UE had set the Follow-on request indicator to "Follow-on request pending" in the REGISTRATION REQUEST message due to pending uplink signalling but cannot send the pending signalling due to new service area restrictions received or due to network not supporting the feature as indicated in the REGISTRATION ACCEPT message (for example UE set the "Follow-on request pending" to send SMS over NAS but AMF notified "SMS over NAS not allowed") and if there is no further pending data or signalling and user plane resources have not been set up, the UE may locally release the established N1 NAS signalling connection upon completion of the registration procedure.
If the timer T3540 is not running when the UE enters state 5GMM-DEREGISTERED.PLMN-SEARCH or 5GMM-REGISTERED.PLMN-SEARCH, the UE may locally release the N1 NAS signalling connection.
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5.3.1.4  5GMM-CONNECTED mode with RRC inactive indicationp. 154

This subclause is only applicable for UE's 5GMM mode over 3GPP access. The 5GMM-CONNECTED mode with RRC inactive indication is not supported when the UE is in NB-N1 mode.
The UE is in 5GMM-CONNECTED mode with RRC inactive indication when the UE is in:
  1. 5GMM-CONNECTED mode over 3GPP access at the NAS layer; and
  2. RRC_INACTIVE state at the AS layer (see TS 38.300).
Unless stated otherwise, the UE behaviour in 5GMM-CONNECTED mode with RRC inactive indication follows the UE behaviour in 5GMM-CONNECTED over 3GPP access, except that:
  1. the UE shall apply the mobility restrictions; and
  2. the UE shall perform the PLMN selection procedures
as in 5GMM-IDLE mode over 3GPP access.
The UE shall transition from 5GMM-CONNECTED mode over 3GPP access to 5GMM-CONNECTED mode with RRC inactive indication upon receiving an indication from the lower layers that the RRC connection has been suspended.
Upon:
  1. a trigger of a procedure which requires sending of a NAS message different from a REGISTRATION REQUEST message with the NG-RAN-RCU bit of the 5GS update type IE set to "UE radio capability update needed";
  2. an uplink user data packet to be sent for a PDU session with suspended user-plane resources;
  3. a trigger to request resources for 5G ProSe direct discovery over PC5 or 5G ProSe direct communication over PC5; or
  4. a trigger to request resources for V2X communication over PC5 (see TS 23.287);
the UE in 5GMM-CONNECTED mode with RRC inactive indication over 3GPP access shall request the lower layers to transition to RRC_CONNECTED state (see TS 38.300).
Upon a trigger to send a REGISTRATION REQUEST message with the NG-RAN-RCU bit of the 5GS update type IE set to "UE radio capability update needed", the UE in 5GMM-CONNECTED mode with RRC inactive indication shall move to 5GMM-IDLE mode over 3GPP access and proceed with the registration procedure for mobility and periodic registration as specified in subclause 5.5.1.3.2.
The UE shall transition from 5GMM-CONNECTED mode with RRC inactive indication to 5GMM-CONNECTED mode over 3GPP access upon receiving an indication from the lower layers that the UE has transitioned to RRC_CONNECTED state (see TS 38.300).
The UE shall trigger a transition from 5GMM-CONNECTED mode with RRC inactive indication to 5GMM-IDLE mode upon selection of a PLMN that is not an equivalent PLMN to the registered PLMN. The UE shall not trigger a transition from 5GMM-CONNECTED mode with RRC inactive indication to 5GMM-IDLE mode upon entering a new PLMN which is in the list of equivalent PLMNs.
The UE shall trigger a transition from 5GMM-CONNECTED mode with RRC inactive indication to 5GMM-IDLE mode upon receiving REFRESH command from the UICC as specified in subclause 5.4.5.3.3.
If the UE in 5GMM-CONNECTED mode with RRC inactive indication receives an indication from the lower layers that the RRC connection has been suspended, the UE shall stay in 5GMM-CONNECTED mode with RRC inactive indication. The UE shall re-initiate any pending procedure that had triggered the request to the lower layers to transition to RRC_CONNECTED state, if still needed.
When the UE in 5GMM-CONNECTED mode with RRC inactive indication receives a fallback indication from lower layers, and the UE has no pending NAS procedure and no pending uplink user data for PDU session(s) with user-plane resources already established, the UE shall:
  1. enter 5GMM-IDLE mode; and
  2. initiate the registration procedure for mobility and periodic registration update as specified for case o) in subclause 5.5.1.3.2.
If the UE requests the lower layers to transition to RRC_CONNECTED state at initiation of a registration procedure, a service request procedure or a de-registration procedure, upon fallback indication from lower layers, the UE shall:
  • enter 5GMM-IDLE mode;
  • proceed with the pending procedure; and
  • if the pending procedure is a service request or registration request procedure and the SERVICE REQUEST message, the CONTROL PLANE SERVICE REQUEST message or the REGISTRATION REQUEST message does not include UE request type IE with Request type value set to "NAS signalling connection release", the UE shall include the Uplink data status IE in the SERVICE REQUEST message, the CONTROL PLANE SERVICE REQUEST message or in the REGISTRATION REQUEST message, indicating the PDU session(s) without active user-plane resources for which the UE has pending user data to be sent, if any, and the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclauses 5.5.1.3 and 5.6.1 for further details).
If the UE requests the lower layers to transition to RRC_CONNECTED state for other reason than initiation of a registration procedure, or for other reason than a service request procedure, or for other reason than a de-registration procedure, upon fallback indication from lower layers, the UE shall:
  1. enter 5GMM-IDLE mode;
  2. initiate the service request procedure and include the Uplink data status IE in the SERVICE REQUEST message or the CONTROL PLANE SERVICE REQUEST message indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclause 5.6.1 for further details). If the procedure that triggered the request to the lower layers to transition to RRC_CONNECTED state is the UE-initiated NAS transport procedure and the UE had SMS, location services message, or CIoT user data to send, the UE shall also include the SMS, location services message, or CIoT user data in the CONTROL PLANE SERVICE REQUEST message as described in subclause 5.6.1.2.2; and
  3. upon successful service request procedure completion, proceed with any pending procedure.
If the UE in 5GMM-CONNECTED mode with RRC inactive indication receives a fallback indication from lower layers, and the UE has pending uplink user data for PDU session(s) with user-plane resources already established but no pending NAS procedure, the UE shall:
  1. enter 5GMM-IDLE mode; and
  2. initiate the service request procedure and include the Uplink data status IE in the SERVICE REQUEST message or the CONTROL PLANE SERVICE REQUEST message indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication (see subclause 5.6.1 for further details).
In the above cases when the UE receives a fallback indication from lower layers, if the UE is in non-allowed area or not in allowed area, the UE shall behave as specified in subclause 5.3.5.
If the UE in 5GMM-CONNECTED mode with RRC inactive indication receives an indication from the lower layers that the resumption of the RRC connection has failed, and:
  1. if the lower layers indicate that access barring is applicable for all access categories except categories 0 and 2, or access barring is applicable for all access categories except category 0, the UE shall:
    1. stay in 5GMM-CONNECTED mode with RRC inactive indication;
  2. else, the UE shall:
    1. enter 5GMM-IDLE mode; and
    2. initiate the registration procedure for mobility and periodic registration update used for mobility (i.e. the 5GS registration type IE set to "mobility registration updating" in the REGISTRATION REQUEST message) for N1 NAS signalling connection recovery as specified for case f) in subclause 5.5.1.3.2.
The UE shall transition from 5GMM-CONNECTED mode with RRC inactive indication to 5GMM-IDLE mode over 3GPP access upon receiving from the lower layers:
  1. indication of transition from RRC_INACTIVE state to RRC_IDLE state; or
  2. indication of cell selection to E-UTRAN or another RAT that the UE supports.
If the UE in 5GMM-CONNECTED mode with RRC inactive indication receives an indication from the lower layers about the cell (re-)selection to different RAT that the UE supports, the UE shall initiate the registration procedure for mobility or periodic registration update used for mobility (i.e. the 5GS registration type IE set to "mobility registration updating" in the REGISTRATION REQUEST message) as specified in subclause 5.5.1.3.2.
If the UE in 5GMM-CONNECTED mode with RRC inactive indication receives an indication from the lower layers of a transition from RRC_INACTIVE state to RRC_IDLE state and 5GMM-REGISTERED.LIMITED-SERVICE is entered, the UE shall subsequently upon entering state 5GMM-REGISTERED.NORMAL-SERVICE and if there is no uplink user data or signalling pending, initiate the registration procedure for mobility and periodic registration update used for mobility (i.e. the 5GS registration type IE set to "mobility registration updating" in the REGISTRATION REQUEST message) for N1 NAS signalling connection recovery as specified in subclause 5.5.1.3.2.
If the UE in 5GMM-CONNECTED mode with RRC inactive indication receives an indication from the lower layers about RAN paging and the MUSIM UE decides not to initiate the service request procedure with service type set to "mobile terminated services" to respond to the RAN paging, the UE may initiate the service request procedure and set request type to "NAS signalling connection release" in the UE request type IE and service type to "signalling" in the SERVICE REQUEST message to reject the RAN paging as specified in subclause 5.6.1.2 for case o of subclause 5.6.1.1. The UE may include its paging restriction preferences in the Paging restriction IE in the SERVICE REQUEST message as specified in subclause 5.6.1.2 for case o of subclause 5.6.1.1.
Upon receiving AMF paging indication from the lower layers, the UE shall transition from 5GMM-CONNECTED mode with RRC inactive indication to 5GMM-IDLE mode over 3GPP access and handle the AMF paging same as the paging request received in the 5GMM-IDLE mode over 3GPP access as specified in subclause 5.6.1.
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5.3.1.5  Suspend and resume of the N1 NAS signalling connection |R16|p. 157

Suspend of the N1 NAS signalling connection can be initiated by the network in 5GMM-CONNECTED mode when user plane CIoT 5GS optimization is used. Resume of the suspended N1 NAS signalling connection is initiated by the UE.
In the UE, when user plane CIoT 5GS optimization is used:
  • Upon idle suspend indication from the lower layers, the UE shall enter 5GMM-IDLE mode with suspend indication, shall not consider the N1 NAS signalling connection released and shall not consider the secure exchange of NAS messages terminated (see subclause 4.4.2.5 and 4.4.5).
  • Upon trigger of a procedure using an initial NAS message when in 5GMM-IDLE mode with suspend indication, the UE shall:
    1. if the initial NAS message is a REGISTRATION REQUEST message with the NG-RAN-RCU bit of the 5GS update type IE set to "UE radio capability update needed", enter 5GMM-IDLE mode without suspend indication and proceed with the registration procedure; or
    2. otherwise, request the lower layer to resume the RRC connection.
  • Upon indication from the lower layers that the RRC connection has been resumed when in 5GMM-IDLE mode with suspend indication, the UE shall enter 5GMM-CONNECTED mode. If the pending NAS message is:
    1. a SERVICE REQUEST message, the service type IE is not set to "emergency services fallback", and the UE did not include the NAS message container IE in the SERVICE REQUEST message; or
    2. a CONTROL PLANE SERVICE REQUEST message, and the UE did not include the CIoT small data container IE or the NAS message container IE in the CONTROL PLANE SERVICE REQUEST message,
    the message shall not be sent. Otherwise the UE shall cipher the message as specified in subclause 4.4.5 and send the pending initial NAS message upon entering 5GMM-CONNECTED mode;
  • Upon fallback indication from the lower layers at RRC connection resume when in 5GMM-IDLE mode with suspend indication, the UE shall enter 5GMM-IDLE mode without suspend indication, send any pending initial NAS message and proceed as if RRC connection establishment had been requested;
  • Upon indication from the lower layers that the RRC connection resume has failed and indication from the lower layers that the RRC connection is suspended, the UE shall enter 5GMM-IDLE mode with suspend indication and restart the ongoing NAS procedure if required; and
  • Upon indication from the lower layers that the RRC connection resume has failed and indication from the lower layers that the RRC connection is not idle suspended, the UE shall enter 5GMM-IDLE mode without suspend indication and restart the ongoing NAS procedure if required.
In the network, when user plane CIoT 5GS optimization is used:
  • Upon idle suspend indication from the lower layers, the network shall enter 5GMM-IDLE mode with suspend indication, shall not consider the N1 NAS signalling connection released and shall not consider the secure exchange of NAS messages terminated; and
  • Upon indication from the lower layers that it has received the NGAP UE context resume request message as specified in TS 38.413 when in 5GMM-IDLE mode with suspend indication, the network shall enter 5GMM-CONNECTED mode.
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