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Content for  TS 24.501  Word version:  18.0.1

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5.6.2  Paging procedurep. 462

5.6.2.1  Generalp. 462

The paging procedure is performed only in 3GPP access and used by the network to request the establishment of a NAS signalling connection to the UE. The paging procedure is also used by the network to request the UE to re-establish the user-plane resources of PDU sessions for downlink user data transport. Another purpose of the paging procedure is to request the UE to re-establish the user-plane resources of PDU session(s) associated with non-3GPP access over 3GPP access.
Additionally, the network can use the paging procedure to initiate the mobile terminating SMS.
For the UE using eDRX, the network initiates the paging procedure when NAS signalling messages or user data is pending to be sent to the UE within the paging time window and requests the lower layers to include the eDRX cycle length and paging time window length in the paging message. If NAS signalling messages or user data is pending to be sent to the UE outside the paging time window and the eDRX value that the network provides to the UE in the Negotiated extended DRX parameters IE during the last registration procedure indicates:
  1. the eDRX cycle length duration of the E-UTRA cell connected to 5GCN, is higher than 5.12 seconds; or
  2. the eDRX cycle length duration of the NR cell connected to 5GCN, is higher than 10.24 seconds,
the network initiates the paging procedure at T time ahead of the beginning of the next paging time window.
If the network detects that the pending user data to be sent to the UE is related to the voice service as specified in TS 23.502 and the network decides to initiate the paging procedure based on the stored paging restriction information, if any, the AMF should request the lower layer to include the Voice Service Indication in the paging message when the UE and the network support the paging indication for voice services.
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5.6.2.2  Paging for 5GS servicesp. 462

5.6.2.2.1  Generalp. 462
The network shall initiate the paging procedure for 5GS services when NAS signalling messages or user data is pending to be sent to the UE in 5GMM-IDLE mode over 3GPP access (see example in Figure 5.6.2.2.1.1) and there is no paging restriction applied in the network for that paging.
Reproduction of 3GPP TS 24.501, Fig. 5.6.2.2.1.1: Paging procedure
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To initiate the procedure the 5GMM entity in the AMF requests the lower layer to start paging and shall start timer T3513.
If downlink signalling or user data is pending to be sent over non-3GPP access, the 5GMM entity in the AMF shall indicate to the lower layer that the paging is associated to non-3GPP access.
The network shall not page the UE to re-establish user-plane resources of PDU session(s) associated with non-3GPP access over 3GPP access if all the PDU sessions of the UE that are established over the 3GPP access are associated with control plane only indication.
If the network has downlink user data pending for a UE, the AMF has stored paging restriction of the UE and the Paging restriction type in the stored paging restriction is set to:
  1. "All paging is restricted", the network should not page the UE;
  2. "All paging is restricted except for voice service", the network should page the UE only when:
    1. the pending downlink user data for the UE is considered as voice service related by the network;
  3. "All paging is restricted except for specified PDU session(s)", the network should page the UE only when:
    1. for PDU session(s) that paging is not restricted based on the stored paging restriction, the network has downlink user data pending; or
  4. "All paging is restricted except for voice service and specified PDU session(s)", the network should page the UE only when:
    1. the pending downlink user data for the UE is considered as voice service related by the network; or
    2. for PDU session(s) that paging is not restricted based on the stored paging restriction, the network has downlink user data pending.
If the network has downlink signalling pending for a UE and the AMF has stored paging restriction of the UE and the Paging restriction type in the stored paging restriction is set to:
  1. "All paging is restricted", the network should not page the UE;
  2. "All paging is restricted except for voice service", the network should page the UE only when:
    1. the pending downlink signalling for the UE is 5GMM signalling or 5GSM signalling of the PDU session of voice service;
  3. "All paging is restricted except for specified PDU session(s)", the network should page the UE only when:
    1. the pending downlink signalling for the UE is 5GMM signalling; or
    2. for PDU session(s) that paging is not restricted based on the stored paging restriction, the network has downlink 5GSM signalling pending; or
  4. "All paging is restricted except for voice service and specified PDU session(s)", the network should page the UE only when:
    1. the pending downlink signalling for the UE is 5GMM signalling or 5GSM signalling of the PDU session of voice service; or
    2. for PDU session(s) that paging is not restricted based on the stored paging restriction, the network has downlink 5GSM signalling pending.
The 5GMM entity in the AMF may provide the lower layer with the "allowed CAG list" and an "indication that the UE is only allowed to access 5GS via CAG cells" for the current PLMN, if available, and with the "allowed CAG list" and an "indication that the UE is only allowed to access 5GS via CAG cells" per equivalent PLMN, if available. If there is an active emergency PDU session, the 5GMM entity in the AMF shall not provide the lower layer with the "allowed CAG list" and an "indication that the UE is only allowed to access 5GS via CAG cells" for the current PLMN, even if available, or with the "allowed CAG list" and an "indication that the UE is only allowed to access 5GS via CAG cells" per equivalent PLMN, even if available.
Upon reception of a paging indication, the UE shall stop the timer T3346, if running, and:
  1. if control plane CIoT 5GS optimization is not used by the UE, the UE shall:
    1. initiate a service request procedure over 3GPP access to respond to the paging as specified in subclauses 5.6.1.2.1 if the UE is in 5GMM-REGISTERED.NORMAL-SERVICE or 5GMM-REGISTERED.NON-ALLOWED-SERVICE (as described in subclause 5.3.5.2) state and the UE is in the 5GMM-IDLE mode without suspend indication;
    2. initiate a service request procedure over non-3GPP access to respond to the paging as specified in subclauses 5.6.1;
    3. initiate a registration procedure for mobility and periodic registration update over 3GPP access to respond to the paging as specified in subclauses 5.5.1.3.2; or
    4. proceed as specified in subclause 5.3.1.5 if the UE is in the 5GMM-IDLE mode with suspend indication; or
  2. if control plane CIoT 5GS optimization is used by the UE, the UE shall:
    1. initiate a service request procedure as specified in subclause 5.6.1.2.2 if the UE is in the 5GMM-IDLE mode without suspend indication;
    2. initiate a registration procedure for mobility and periodic registration update over 3GPP access as specified in subclauses 5.5.1.3.2; or
    3. proceed as specified in subclause 5.3.1.5 if the UE is in the 5GMM-IDLE mode with suspend indication.
The MUSIM UE based on implementation may use the paging cause indicated by lower layers (see TS 38.331), if any, to accept the paging, reject the paging or ignore the paging indication.
Upon reception of a paging indication, if the network supports the rejection of paging request and if a MUSIM UE decides not to accept the paging, the UE may initiate a service request procedure to reject the paging as specified in clause 5.6.1.1.
If TMGI is used as paging identity and the TMGI matches with MBS multicast session which the has UE joined, the UE shall respond to the paging. Otherwise, the UE shall not respond to the paging.
The network shall stop timer T3513 for the paging procedure when an integrity-protected response is received from the UE and successfully integrity checked by the network or when the 5GMM entity in the AMF receives an indication from the lower layer that it has received the NGAP UE context resume request message as specified in TS 38.413. If the response received is not integrity protected, or the integrity check is unsuccessful, timer T3513 for the paging procedure shall be kept running unless:
  1. the UE is registered for emergency services;
  2. the UE has an emergency PDU session; or
  3. the response received is a REGISTRATION REQUEST message for mobility and periodic registration update and the security mode control procedure or authentication procedure performed during mobility and periodic registration update has completed successfully.
Upon expiry of timer T3513, the network may reinitiate paging.
If the network, while waiting for a response to the paging sent without paging priority, receives downlink signalling or downlink data associated with priority user-plane resources for PDU sessions, the network shall stop timer T3513, and then initiate the paging procedure with paging priority.
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5.6.2.2.2  Abnormal cases on the network sidep. 465
The following abnormal case can be identified:
  1. Void.
5.6.2.2.3  Abnormal cases in the UEp. 465
The following abnormal cases can be identified:
  1. Paging message received with access type set to non-3GPP access while the UE is in 5GMM-CONNECTED mode over non-3GPP access.
    The UE shall not respond to paging message.
  2. Paging message received with access type set to 3GPP access when UE-initiated 5GMM specific procedure or service request procedure is ongoing.
    The UE shall proceed with 5GMM specific procedure or service request procedure. If for these procedures lower layers indicate that the access attempt is barred, then the UE shall handle the pending paging message as specified in subclause 5.6.2.2.1. Otherwise, the UE shall ignore the paging once lower layers confirm the establishment of the signalling connection.
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5.6.3  Notification procedurep. 465

5.6.3.1  Generalp. 465

The notification procedure is used by the network:
  1. to request the UE, by sending the NOTIFICATION message over 3GPP access, to re-establish the user-plane resources of PDU session(s) associated with non-3GPP access over 3GPP access or to deliver 5GSM downlink signalling messages associated with non-3GPP access over 3GPP access when the UE is in 5GMM-IDLE mode over non-3GPP access and in 5GMM-CONNECTED mode over 3GPP access; or
  2. to request the UE, by sending the NOTIFICATION message over non-3GPP access, to re-establish user-plane resources of the PDU session(s) or to deliver downlink signalling associated with 3GPP access over 3GPP access when the UE is in 5GMM-CONNECTED mode over non-3GPP access and:
    1. in 5GMM-IDLE mode over 3GPP access when the UE is not in MICO mode; or
    2. in 5GMM-IDLE mode with suspend indication over 3GPP access when the UE is not in MICO mode.
The network shall not use the NOTIFICATION message to re-establish user-plane resources of PDU session(s) associated with non-3GPP access over 3GPP access if all the PDU sessions of the UE that are established over the 3GPP access are associated with control plane only indication.
The network shall not use the NOTIFICATION message over non-3GPP access, if:
  1. the MUSIM UE supports the paging indication for voice services;
  2. the network has indicated "paging indication for voice services supported" to the UE; and
  3. the AMF detects that the downlink data is related to voice service (see TS 23.501).
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5.6.3.2  Notification procedure initiationp. 466

The network shall initiate the notification procedure by sending the NOTIFICATION message to the UE and start timer T3565 (see example in Figure 5.6.3.2.1).
For case a) in subclause 5.6.3.1, the NOTIFICATION message is sent from the network to the UE via 3GPP access with access type indicating non-3GPP access.
For case b) in subclause 5.6.3.1, the NOTIFICATION message is sent from the network to the UE via non-3GPP access with access type indicating 3GPP access when the UE is not in MICO mode.
Reproduction of 3GPP TS 24.501, Fig. 5.6.3.2.1: Notification procedure
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Upon reception of a NOTIFICATION message, the UE shall stop the timer T3346, if running.
For case a) in subclause 5.6.3.1, upon reception of NOTIFICATION message, the UE shall initiate a service request procedure over 3GPP access as specified in subclauses 5.6.1.
For case b) in subclause 5.6.3.1, upon reception of NOTIFICATION message:
  1. if control plane CIoT 5GS optimization is not used by the UE, the UE shall:
    1. initiate a service request procedure over 3GPP access as specified in subclause 5.6.1.2.1, if the UE is in 5GMM-REGISTERED.NORMAL-SERVICE or 5GMM-REGISTERED.NON-ALLOWED-SERVICE (as described in subclause 5.3.5.2) state over 3GPP access or 5GMM-REGISTERED.NON-ALLOWED-SERVICE state (see subclause 5.3.5.2), and the UE is in the 5GMM-IDLE mode without suspend indication;
    2. initiate a registration procedure for mobility and periodic registration update over 3GPP access as specified in subclause 5.5.1.3.2, if the UE is in 5GMM-REGISTERED.ATTEMPTING-REGISTRATION-UPDATE state over 3GPP access; or
    3. proceed as specified in subclause 5.3.1.5 if the UE is in the 5GMM-IDLE mode with suspend indication;
  2. if control plane CIoT 5GS optimization is used by the UE, the UE shall:
    1. initiate a service request procedure over 3GPP access as specified in subclause 5.6.1.2.2, if the UE is in 5GMM-REGISTERED.NORMAL-SERVICE or 5GMM-REGISTERED.NON-ALLOWED-SERVICE (as described in subclause 5.3.5.2) state and the UE is in the 5GMM-IDLE mode without suspend indication;
    2. initiate a registration procedure for mobility and periodic registration update over 3GPP access as specified in subclause 5.5.1.3.2, if the UE is in 5GMM-REGISTERED.ATTEMPTING-REGISTRATION-UPDATE state; or
    3. proceed as specified in subclause 5.3.1.5 if the UE is in the 5GMM-IDLE mode with suspend indication; or
  3. if:
    1. the UE is in 5GMM-REGISTERED.NO-CELL-AVAILABLE state, 5GMM-REGISTERED.PLMN-SEARCH state, 5GMM-REGISTERED.LIMITED-SERVICE state or 5GMM-REGISTERED.UPDATE-NEEDED state over 3GPP access; or
    2. the MUSIM UE is not able to respond the NOTIFICATION message as specified in case a) and b) above, e.g., due to UE implementation constraints;
    the UE shall respond with NOTIFICATION RESPONSE message over non-3GPP access indicating inability of the UE to initiate a service request procedure or a registration procedure over 3GPP access and may include the PDU session status information element to indicate:
    1. the single access PDU session(s) not in 5GSM state PDU SESSION INACTIVE in the UE associated with the 3GPP access type; and
    2. the MA PDU session(s) not in 5GSM state PDU SESSION INACTIVE in the UE and having user plane resources established associated with the 3GPP access type.
Upon reception of NOTIFICATION message:
For case b) in subclause 5.6.3.1, if the UE is in 5GMM-REGISTERED.NO-CELL-AVAILABLE state or 5GMM-REGISTERED.PLMN-SEARCH state and a local release was performed in the UE for the single access PDU sessions associated with the 3GPP access or for user plane resources on the 3GPP access of MA PDU sessions;
then the UE shall respond with NOTIFICATION RESPONSE message over non-3GPP access indicating with the PDU session status information element that:
  • the local release of its single access PDU sessions associated with the 3GPP access was performed; and
  • the local release of its 3GPP access user plane resources of MA PDU sessions was performed.
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5.6.3.3  Notification procedure completionp. 467

Upon reception of SERVICE REQUEST message, CONTROL PLANE SERVICE REQUEST message or REGISTRATION REQUEST message, the AMF shall stop timer T3565 and proceed service request procedure as specified in subclauses 5.6.3.1 or registration procedure for mobility and periodic registration update as specified in subclauses 5.5.1.3. If no user-plane resources of PDU session(s) need to be re-established, the AMF should notify the SMF that the UE was reachable but did not accept to re-establish the user-plane resources of PDU session(s).
When the 5GMM entity in the AMF receives an indication from the lower layer that it has received the NGAP UE context resume request message as specified in TS 38.413, the AMF shall stop timer T3565.
Upon reception of NOTIFICATION RESPONSE message over non-3GPP access, the AMF shall stop timer T3565 and should notify the SMF that the UE is unreachable.
If the NOTIFICATION RESPONSE message includes the PDU session status information element, then:
  1. for single access PDU sessions, the AMF shall:
    1. perform a local release of all those PDU sessions which are not in 5GSM state PDU SESSION INACTIVE on the AMF side associated with 3GPP access, but are indicated by the UE in the PDU session status information element in the NOTIFICATION RESPONSE message as being in 5GSM state PDU SESSION INACTIVE; and
    2. shall request the SMF to perform a local release of all those PDU sessions associated with 3GPP access. If any of those PDU sessions is associated with one or more MBS sessions, the SMF shall consider the UE as removed from the associated MBS sessions; and
  2. For MA PDU sessions, the AMF shall:
    1. for MA PDU sessions having user plane resources established only on the 3GPP access in the AMF side, but are indicated by the UE in the PDU session status information element in the NOTIFICATION RESPONSE message as no user plane resources established on the 3GPP access:
      1. perform a local release of all those MA PDU sessions; and
      2. request the SMF to perform a local release of all those MA PDU sessions. If the MA PDU session is associated with one or more MBS sessions, the SMF shall consider the UE as removed from the associated MBS sessions; and
    2. for MA PDU sessions having user plane resources established on both accesses in the AMF side, but are indicated by the UE in the PDU session status information element in the NOTIFICATION RESPONSE message as no user plane resources established on the 3GPP access:
      1. perform a local release of 3GPP access user plane resources of all those MA PDU sessions; and
      2. request the SMF to perform a local release of 3GPP access user plane resources of all those MA PDU sessions. If the MA PDU session is associated with one or more MBS sessions, the SMF shall consider the UE as removed from the associated MBS sessions.
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5.6.3.4  Abnormal cases on the network sidep. 468

The following abnormal cases can be identified:
  1. Expiry of timer T3565.
    The network shall, on the first expiry of the timer T3565, retransmit the NOTIFICATION message and shall reset and start timer T3565. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3565, the procedure shall be aborted. In addition, upon the fifth expiry of timer T3565:
    For case a) in subclause 5.6.3.1, the AMF should notify the SMF that the UE is unreachable. The AMF may enter 5GMM-IDLE mode over 3GPP access.
    For case b) in subclause 5.6.3.1, the AMF may either:
    1. perform the paging procedure over the 3GPP access; or
    2. notify the SMF that the UE is unreachable.
  2. De-registration procedure collision
    If the network receives a DEREGISTRATION REQUEST message before it receives a SERVICE REQUEST message or REGISTRATION REQUEST message, the AMF shall stop timer T3565 and proceed de-registration procedure as specified in subclause 5.5.2.
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5.6.3.5  Abnormal cases on the UE sidep. 469

The following abnormal cases can be identified:
  1. NOTIFICATION message received via non-3GPP access with access type indicating 3GPP access when UE-initiated 5GMM specific procedure or service request procedure over 3GPP access is ongoing.
    The UE shall proceed with 5GMM specific procedure or service request procedure. If for these procedures lower layers indicate that the access attempt is barred, then the UE shall handle the pending NOTIFICATION message as specified in subclause 5.6.3.2. Otherwise, the UE shall ignore the NOTIFICATION message once lower layers confirms the establishment of the signalling connection.
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