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full Contents for  TS 23.502  Word version:   16.4.0

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1…   4.2.2.2.2   4.2.2.2.3…   4.2.3…   4.2.3.3   4.2.4…   4.2.6   4.2.7…   4.2.9…   4.3…   4.3.2.2…   4.3.2.2.2   4.3.2.2.3…   4.3.3   4.3.4   4.3.5…   4.3.5.2…   4.3.5.4…   4.3.5.6…   4.3.6…   4.4…   4.5…   4.9…   4.9.1.3…   4.9.2…   4.11…   4.11.1.2.2…   4.11.1.3…   4.11.1.4…   4.11.1.5…   4.11.2   4.11.3…   4.12…   4.12.6…   4.12a   4.12b   4.13…   4.13.4…   4.13.6…   4.14…   4.15…   4.15.4…   4.16…   4.16.4…   4.16.8…   4.17…   4.17.9…   4.18…   4.19…   4.23…   4.23.7…   4.23.9…   4.23.11…   4.24   4.25   4.26…   5…   5.2.3…   5.2.5…   5.2.6…   5.2.7…   5.2.8…   5.2.9…   5.2.12…   A…   E…   F…

 

4.2.2.2.3  Registration with AMF re-allocationWord-p. 40
When an AMF receives a Registration request, the AMF may need to reroute the Registration request to another AMF, e.g. when the initial AMF is not the appropriate AMF to serve the UE. The Registration with AMF re-allocation procedure, described in figure 4.2.2.2.3-1, is used to reroute the NAS message of the UE to the target AMF during a Registration procedure.
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The initial AMF and the target AMF register their capability at the NRF.
Step 1.
Steps 1 and 2 of figure 4.2.2.2.2-1 have occurred, and the (R)AN sends the Registration request message within an Initial UE message to the initial AMF.
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Step 2.
If the AMF needs the SUPI and/or UE's subscription information to decide whether to reroute the Registration Request or if the Registration Request was not sent integrity protected or integrity protection is indicated as failed, then AMF performs steps 4 to 9a or to 9b of figure 4.2.2.2.2-1.
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Step 3a.
[Conditional] If the initial AMF needs UE's subscription information to decide whether to reroute the Registration Request and UE's slice selection subscription information was not provided by old AMF, the AMF selects a UDM as described in TS 23.501, clause 6.3.8.
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Step 3b.
Initial AMF to UDM: Nudm_SDM_Get (SUPI, Slice Selection Subscription data).
The initial AMF request UE's Slice Selection Subscription data from UDM by invoking the Nudm_SDM_Get (see clause 5.2.3.3.1) service operation. UDM may get this information from UDR by Nudr_DM_Query(SUPI, Slice Selection Subscription data).
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Step 3c.
UDM to initial AMF: Response to Nudm_SDM_Get. The AMF gets the Slice Selection Subscription data including Subscribed S-NSSAIs.
UDM responds with slice selection data to initial AMF.
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Step 4a.
[Conditional] Initial AMF to NSSF: Nnssf_NSSelection_Get (Requested NSSAI, [Mapping Of Requested NSSAI], Subscribed S-NSSAI(s) with the default S-NSSAI indication, TAI, Allowed NSSAI for the other access type (if any), [Mapping of Allowed NSSAI], PLMN ID of the SUPI).
If there is a need for slice selection, (see clause 5.15.5.2.1 of TS 23.501), e.g. the initial AMF cannot serve all the S-NSSAI(s) from the Requested NSSAI permitted by the subscription information, the initial AMF invokes the Nnssf_NSSelection_Get service operation from the NSSF by including Requested NSSAI, optionally Mapping Of Requested NSSAI, Subscribed S-NSSAIs with the default S-NSSAI indication, Allowed NSSAI for the other access type (if any), Mapping of Allowed NSSAI, PLMN ID of the SUPI and the TAI of the UE.
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Step 4b.
[Conditional] NSSF to Initial AMF: Response to Nnssf_NSSelection_Get (AMF Set or list of AMF addresses, Allowed NSSAI for the first access type, [Mapping Of Allowed NSSAI], [Allowed NSSAI for the second access type], [Mapping of Allowed NSSAI], [NSI ID(s)], [NRF(s)], [List of rejected (S-NSSAI(s), cause value(s))], [Configured NSSAI for the Serving PLMN], [Mapping Of Configured NSSAI]).
The NSSF performs the steps specified in point (B) in clause 5.15.5.2.1 of TS 23.501. The NSSF returns to initial AMF the Allowed NSSAI for the first access type, optionally the Mapping Of Allowed NSSAI, the Allowed NSSAI for the second access type (if any), optionally the Mapping of Allowed NSSAI and the target AMF Set or, based on configuration, the list of candidate AMF(s). The NSSF may return NSI ID(s) associated to the Network Slice instance(s) corresponding to certain S-NSSAI(s). The NSSF may return the NRF(s) to be used to select NFs/services within the selected Network Slice instance(s). It may return also information regarding rejection causes for S-NSSAI(s) not included in the Allowed NSSAI. The NSSF may return Configured NSSAI for the Serving PLMN, and possibly the associated mapping of the Configured NSSAI.
NOTE:
The NRF(s) returned by the NSSF, if any, belong to any level of NRF (see clause 6.2.6 of TS 23.501) according to the deployment decision of the operator.
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Step 5.
[Conditional] Initial AMF to old AMF: Namf_Communication_RegistrationStatusUpdate (failure cause ).
If another AMF is selected, the initial AMF sends a reject indication to the old AMF telling that the UE Registration procedure did not fully complete at the initial AMF. The old AMF continues as if the Namf_Communication_UEContextTransfer had never been received.
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Step 6a.
[Conditional] Initial AMF to NRF: Nnrf_NFDiscovery_Request (NF type, AMF Set).
If the initial AMF does not locally store the target AMF address, and if the initial AMF intends to use direct reroute to target AMF or the reroute via (NG-R)AN message needs to include AMF address, then the initial AMF invokes the Nnrf_NFDiscovery_Request service operation from the NRF to find a proper target AMF which has required NF capabilities to serve the UE. The NF type is set to AMF. The AMF Set is included in the Nnrf_NFDiscovery_Request.
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Step 6b.
[Conditional] NRF to AMF: Response to Nnrf_NFDiscovery_Request (list of (AMF pointer, AMF address, plus additional selection rules and NF capabilities)).
The NRF replies with the list of potential target AMF(s). The NRF may also provide the details of the services offered by the candidate AMF(s) along with the notification end-point for each type of notification service that the selected AMF had registered with the NRF, if available. As an alternative, it provides a list of potential target AMFs and their capabilities, and optionally, additional selection rules. Based on the information about registered NFs and required capabilities, a target AMF is selected by the initial AMF.
If the initial AMF is not part of the target AMF set, and is not able to get a list of candidate AMF(s) by querying the NRF with the target AMF set (e.g. the NRF locally pre-configured on AMF does not provide the requested information, the query to the appropriate NRF provided by the NSSF is not successful, or the initial AMF has knowledge that the initial AMF is not authorized as serving AMF etc.) then the initial AMF shall forward the NAS message to the target AMF via (R)AN executing step 7(B); the Allowed NSSAI and the AMF Set are included to enable the (R)AN to select the target AMF as described in TS 23.501, clause 6.3.5.
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Step 7(A).
If the initial AMF, based on local policy and subscription information, decides to forward the NAS message to the target AMF directly, the initial AMF invokes the Namf_Communication_N1MessageNotify to the target AMF, carrying the rerouted NAS message. The Namf_Communication_N1MessageNotify service operation includes the information enabling (R)AN to identify the N2 terminating point, and the full Registration Request message, and the UE's SUPI and MM Context if available. If the initial AMF has obtained the information from the NSSF as described at step 4b, that information except the AMF Set or list of AMF addresses is included. The target AMF then updates the (R)AN with a new updated N2 termination point for the UE in the first message from target AMF to RAN in step 8.
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Step 7(B).
If the initial AMF, based on local policy and subscription information, decides to forward the NAS message to the target AMF via (R)AN unless the target AMF(s) are returned from the NSSF and identified by a list of candidate AMF(s), the initial AMF sends a Reroute NAS message to the (R)AN (step 7a). The Reroute NAS message includes the information about the target AMF, and the full Registration Request message. If the initial AMF has obtained the information as described at step 4b, that information is included. The (R)AN sends the Initial UE message to the target AMF (step 7b) indicating reroute due to slicing including the information from step 4b that the NSSF provided.
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Step 8.
After receiving the Registration Request message transmitted at step 7(A)a or step 7(B)b, the target AMF continues with the Registration procedure from step 4 until 22 of figure 4.2.2.2.2-1 (with the target AMF corresponding to the new AMF), which includes the UE context retrieved from old AMF. If the 5G security context is received from the initial AMF, the target AMF continue using that one instead of the 5G security context retrieved from old AMF. If the initial AMF decides to forward the NAS message to the target AMF (step 7(A), the first message from the target AMF to (R)AN (either Initial Context Setup Request, or Downlink NAS Transport) contain the AMF name of the initial AMF and target AMF UE NGAP ID.
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4.2.2.3  Deregistration proceduresWord-p. 43
4.2.2.3.1  General
The Deregistration procedure allows:
  • the UE to inform the network that it does not want to access the 5GS any longer, and
  • the network to inform the UE that it does not have access to the 5GS any longer.
The Deregistration request by the UE and Deregistration request by the network include whether the Deregistration applies to the 3GPP access, to the non-3GPP access, or to both. When the UE is registered to both accesses in the same PLMN, the Deregistration message can be sent over any access regardless of the access the Deregistration is applied to.
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4.2.2.3.2  UE-initiated Deregistration
The UE uses this procedure to deregister from the registered PLMN as shown in Figure 4.2.2.3.2-1.
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Step 1.
The UE sends NAS message Deregistration Request (5G-GUTI, Deregistration type (e.g. Switch off), Access Type) to the AMF.
Access type indicates whether the Deregistration procedure applies to the 3GPP access, to the non-3GPP access, or to both if the 3GPP access and non-3GPP access of the UE are served by the same AMF (refer to TS 23.501). The AMF shall invoke the Deregistration procedure for the target access indicated by the UE.
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Step 2.
[Conditional] AMF to SMF: Nsmf_PDUSession_ReleaseSMContext (SM Context ID).
If the UE has no established PDU Session over the target access indicated in step 1, then steps 2 to 5 are not executed. All PDU Sessions over the target access(es), which belong to the UE are released by the AMF sending Nsmf_PDUSession_ReleaseSMContext Request (SM Context ID) message to the SMF for each PDU Session.
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Step 3.
[Conditional] The SMF releases all resources e.g. the IP address / Prefix(es) that were allocated to the PDU Session and releases the corresponding User Plane resources:
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Step 3a.
[Conditional] The SMF sends N4 Session Release Request (N4 Session ID) message to the UPF(s) of the PDU Session. The UPF(s) shall drop any remaining packets of the PDU Session and release all tunnel resource and contexts associated with the N4 Session.
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Step 3b.
[Conditional] The UPF(s) acknowledges the N4 Session Release Request by the transmission of an N4 Session Release Response (N4 Session ID) message to the SMF.
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Step 4.
[Conditional] The SMF responds with Nsmf_PDUSession_ReleaseSMContext Response message.
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Step 5a.
[Conditional] If dynamic PCC applied to this session the SMF performs an SM Policy Association Termination procedure as defined in clause 4.16.6.
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Step 5b-c.
[Conditional] If it is the last PDU Session the SMF is handling for the UE for the associated (DNN, S-NSSAI), the SMF unsubscribes from Session Management Subscription data changes notification with the UDM by means of the Nudm_SDM_Unsubscribe service operation. The SMF invokes the Nudm_UECM_Deregistration service operation so that the UDM removes the association it had stored between the SMF identity and the associated DNN and PDU Session Id.
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Step 6.
[Conditional] If there is any association with the PCF for this UE and the UE is no more registered over any access, the AMF performs a AMF-initiated AM Policy Association Termination procedure as defined in clause 4.16.3.2 delete the association with the PCF.
6a. [Conditional] If there is any association with the PCF for this UE and the UE is no more registered over any access, the AMF performs a AMF-initiated UE Policy Association Termination procedure as defined in clause 4.16.13.1 delete the association with the PCF.
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Step 7.
[Conditional] The AMF sends NAS message Deregistration Accept to UE depending on the Deregistration type i.e. if Deregistration type is switch-off, AMF does not send Deregistration Accept message.
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Step 8.
[Conditional] AMF to AN: N2 UE Context Release Request (Cause)
If the target access for Deregistration procedure is 3GPP access or both 3GPP access and non-3GPP access, and there is N2 signalling connection to NG-RAN, the AMF sends N2 UE Release command to NG-RAN with Cause set to Deregistration to release N2 signalling connection. The details of this step are covered by steps 2 to 4 in the AN Release procedure, as described in clause 4.2.6.
If the target access for Deregistration procedure is non-3GPP access or both 3GPP access and non-3GPP access, and there is N2 signalling connection to the N3IWF/TNGF/W-AGF, the AMF sends N2 UE Release command to N3IWF/TNGF/W-AGF with Cause set to Deregistration to release N2 signalling connection. The details of this step are covered by steps 2 to 5 in the "Deregistration procedure for (un)trusted non-3gpp access", as described in clauses 4.12.3 / 4.12a.3 and in clause 7.2.1 in TS 23.316 for W-5GAN access.
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4.2.2.3.3  Network-initiated DeregistrationWord-p. 45
The procedure depicted in Figure 4.2.2.3.3-1 shows Network-initiated Deregistration procedure. The AMF can initiate this procedure for either explicit (e.g. by O&M intervention or if the AMF determines that no S-NSSAI can be provided in the Allowed NSSAI for the UE) or implicit (e.g. expiring of Implicit Deregistration timer). The UDM can trigger this procedure for operator-determined purposes to request the removal of a subscriber's RM context and PDU Session(s) of the UE.
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Step 1.
[Conditional] If the UDM wants to request the immediate deletion of a subscriber's RM contexts and PDU Sessions, the UDM shall send a Nudm_UECM_DeregistrationNotification (SUPI, Access Type, Removal Reason) message with Removal Reason set to Subscription Withdrawn to the registered AMF. The Access Type may indicate 3GPP Access, non-3GPP Access or both.
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Step 2.
If the AMF receives Nudm_UECM_DeregistrationNotification in Step 1 with Removal Reason as Subscription Withdrawn, the AMF executes Deregistration procedure over the access(es) the Access Type indicates.
The AMF-initiated Deregistration procedure is either explicit (e.g. by O&M intervention or if the AMF determines that no S-NSSAI can be provided in the Allowed NSSAI for the UE) or implicit. The AMF does not send the Deregistration Request message to the UE for Implicit Deregistration. If the UE is in CM-CONNECTED state, the AMF may explicitly deregister the UE by sending a Deregistration Request message (Deregistration type, Access Type, [list of Rejected S-NSSAIs, each of them with the appropriate rejection cause value]) to the UE. The Deregistration type may be set to Re-registration in which case the UE should re-register at the end of the Deregistration procedure. Access Type indicates whether Deregistration procedure applies to the 3GPP access or non-3GPP access, or both. If the Deregistration Request message is sent over 3GPP access and the UE is in CM-IDLE state in 3GPP access, the AMF pages the UE. The list of Rejected S-NSSAIs, each of them with the appropriate rejection cause value, is provided if the AMF determines that no S-NSSAI can be provided to the UE in the Allowed NSSAI.
If the UE has established PDU Session associated with emergency service, the AMF shall not initiate Deregistration procedure. In this case, the AMF performs network requested PDU Session Release for any PDU session associated with non-emergency service as described in clause 4.3.4.
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Step 3.
[Conditional] If the Deregistration procedure is triggered by UDM (Step 1), the AMF acknowledges the Nudm_UECM_DeRegistrationNotification to the UDM.
If Access Type indicates 3GPP Access or non-3GPP Access and AMF does not have UE context for another access type, or if Access Type indicates both, the AMF unsubscribes with the UDM using Nudm_SDM_Unsubscribe service operation.
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Step 4.
[Conditional] If the UE has any established PDU Session over the target access for deregistration indicated in step 2, then step 2 ~ step 5 of UE-initiated Deregistration procedure in clause 4.2.2.3.2 is performed.
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Step 5.
[Conditional] As in step 6 of Figure 4.2.2.3.2-1.
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Step 5a.
[Conditional] As in step 6a of Figure 4.2.2.3.2-1.
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Step 6.
[Conditional] If the UE receives the Deregistration Request message from the AMF in step 2, the UE sends a Deregistration Accept message to the AMF any time after step 2. The NG-RAN forwards this NAS message to the AMF along with the TAI+ Cell identity of the cell which the UE is using.
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Step 7.
[Conditional] AMF to AN: N2 UE Context Release Request (Cause): as in step 8 of Figure 4.2.2.3.2.
If the UE is deregistered over only 3GPP access or non-3GPP access and the AMF does not have UE context for the other, or if the procedure applies to both access types, then at any time, AMF can unsubscribe from the UDM, otherwise the AMF can deregister from UDM using Nudm_UECM_Deregistration request by indicating its associating access type.
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