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Content for  TS 23.502  Word version:  17.6.0

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4.2.2.2.3  Registration with AMF re-allocationp. 48
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.
Reproduction of 3GPP TS 23.502, Fig. 4.2.2.2.3-1: Registration with AMF re-allocation procedure
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The initial AMF and the target AMF register their capability at the NRF.
Step 1.
If the UE is in CM-IDLE State, 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. If the UE is in CM-CONNECTED state and triggers registration procedure, the NG-RAN sends Registration request message in the Uplink NAS Transport message to the serving AMF which is initial AMF. The AMF may skip step 2-3.
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.
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 clause 6.3.8 of TS 23.501.
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).
For a Disaster Roaming Registration, the AMF may provide the indication of Disaster Roaming service to the UDM.
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 subscription data to initial AMF.
For a Disaster Roaming Registration, the UDM responds with the slice selection subscription data for a Disaster Roaming service to initial AMF based on the local policy and/or the local configuration as specified in clause 5.40.4 of TS 23.501.
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,
[NSSRG Information],
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, [NSSRG Information], Allowed NSSAI for the other access type (if any), Mapping of Allowed NSSAI, PLMN ID of the SUPI and the TAI of the UE.
The AMF includes, if available, the NSSRG Information for the S-NSSAIs of the HPLMN, defined in clause 5.15.12 of TS 23.501, including information whether the UE has indicated support of the subscription-based restrictions to simultaneous registration of network slices and whether the UDM has indicated to provide all subscribed S-NSSAIs for non-supporting UEs.
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. If the NSSRG information was included in the request, the NSSF provides the Configured NSSAI as described in clause 5.15.12 of TS 23.501.
Step 5.
[Conditional] Initial AMF to old AMF: Namf_Communication_RegistrationStatusUpdate (failure cause).
If the UE was in CM-IDLE and 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.
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.
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 security association has been established between the UE and initial AMF, to avoid a registration failure, the initial AMF shall forward the NAS message to the target AMF by executing step 7(A).
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) unless the security association has been established between the UE and initial AMF; the Allowed NSSAI and the AMF Set are included to enable the (R)AN to select the target AMF as described in clause 6.3.5 of TS 23.501.
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 AN access information (e.g. the information enabling (R)AN to identify the N2 terminating point, CAG Identifier(s) of the CAG cell) and the complete Registration Request message in clear text as specified in TS 33.501 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.
Step 7(B).
[Conditional] if the UE was in CM-IDLE, 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 NGAP Reroute NAS Request message to the (R)AN (step 7a). The NGAP Reroute Request NAS message includes the information about the target AMF and the complete 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.
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 the target AMF may have retrieved from the 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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4.2.2.2.4  Registration with Onboarding SNPN |R17|p. 52
This clause specifies how a UE can register to an ON-SNPN for provisioning the UE with SO-SNPN credentials and other information to enable SNPN access as defined in clause 5.30.2.10 of TS 23.501.
The Registration procedure for Onboarding SNPN shall be supported as specified in clause 4.2.2.2.2 with the following changes compared to the steps in the call flow represented in Figure 4.2.2.2.2-1, covering three cases, i.e. when DCS is hosting AAA Server and when DCS is hosting AUSF/UDM and when DCS is not involved, as shown in Figure 4.2.2.2.4-1.
Reproduction of 3GPP TS 23.502, Fig. 4.2.2.2.4-1: UE Registration with ON-SNPN
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Step 1.
UE to NG-RAN: AN parameters shall include Onboarding indication if the UE is accessing 5GS for Onboarding. The Registration Type "SNPN Onboarding" indicates that the UE wants to perform SNPN Onboarding Registration (i.e. allows the UE to access an ON-SNPN for the purpose of provisioning the UE with SO-SNPN credentials). For SNPN Onboarding Registration, a SUCI generated from a SUPI derived from Default UE Credentials shall be included as described in clause 5.30.2.10.2.6 of TS 23.501.
If the UE has registered in the ON-SNPN for onboarding, the UE can perform a Mobility Registration Update, or a Periodic Registration Update as specified in clause 4.2.2.2.2. If the onboarding registered UE wants to perform a Mobility Registration Update the AN parameters shall also include an Onboarding indication that the UE is registered for onboarding.
Step 2.
Based on the Onboarding indication in step 1, the NG-RAN selects an AMF as described in clause 6.3.5 of TS 23.501.
Step 3.
NG-RAN to AMF: The N2 message contains the Registration Request as described in step 1.
Step 4.
[Conditional] new AMF to old AMF: Namf_Communication_UEContextTransfer (complete Registration Request).
Step 5.
[Conditional] old AMF to new AMF: Response to Namf_Communication_UEContextTransfer (SUPI, UE Context in AMF (as per Table 5.2.2.2.2-1)). Once the registration is completed successfully, the new AMF may start an implementation specific deregistration timer for when to deregister the onboarding registered UE if the UE context contains the indication that the UE is registered for onboarding.
Step 6-7.
Skipped.
Step 8.
When the AMF receives a NAS Registration Request with the 5GS Registration Type set to "SNPN Onboarding", the AMF applies locally configured AMF Configuration Data for Onboarding in order to restrict UE network usage to only onboarding and stores in the UE Context in AMF an indication that the UE is registered for onboarding. The AMF selects an AUSF as described in clause 5.30.2.10.2.6 of TS 23.501. Based on ON-SNPN policies, the AMF may start an implementation specific deregistration timer configured for UE Onboarding as described in TS 23.501.
Step 9.
The authentication is performed as described in TS 33.501.
For DCS hosting AAA Server as shown in step 9-1, based on local configuration (e.g. using the realm part of the SUCI), the AUSF sends the SUPI towards the AAA Server in the DCS domain via the NSSAAF, then the AAA Server in the DCS domain authenticates the UE based on received data from AUSF. During authentication procedure the AAA Server in the DCS domain may provide PVS FQDN(s) and/or PVS IP address(es) for the UE to the AUSF via the NSSAAF, the AUSF then provides PVS FQDN(s) and/or PVS IP address(es) to the AMF.
For DCS hosting AUSF/UDM as shown in step 9-2, the AUSF in DCS domain performs UDM selection. The AMF sends the SUCI and Default UE credentials received from the UE towards the AUSF in DCS domain, which authenticates the UE based on received data from AMF and subscription data from the UDM in DCS domain. During authentication procedure, the AUSF in the DCS domain provides PVS FQDN(s) and/or PVS IP address(es) to the AMF.
When DCS is not involved during primary authentication as shown in step 9-3, the AMF selects a local AUSF as defined in clause 6.3.4 of TS 23.501 and performs primary authentication towards the local AUSF using Default UE credentials as described in TS 33.501.
Step 10.
[Conditional] new AMF to old AMF: Namf_Communication_RegistrationStatusUpdate.
Step 11.
[Conditional] AMF to UE: Identity Request/Response (PEI).
If the PEI was not provided by the UE, the Identity Request procedure is initiated by AMF sending an Identity Request message to the UE to retrieve the PEI.
Step 12.
Optionally the new AMF initiates ME identity check by invoking the N5g-eir_EquipmentIdentityCheck_Get service operation (see clause 5.2.4.2.2).
The PEI check is performed as described in clause 4.7.
Step 13-20.
Skipped.
Step 21.
AMF to UE: The AMF sends a Registration Accept message to the UE indicating that the Registration Request for Onboarding SNPN has been accepted. The Allowed NSSAI containing the S-NSSAI from the AMF Onboarding Configuration Data is included in the N2 message to NG-RAN.
Step 21b.
Skipped.
Step 22.
UE to AMF: The UE sends a Registration Complete message to the AMF.
Step 23-25.
Skipped.
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4.2.2.3  Deregistration proceduresp. 53

4.2.2.3.1  Generalp. 53
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; or
  • the network to inform the UE that the UE's Registered PLMN is not allowed to operate at the UE location.
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.
Network-initiated Deregistration may be initiated if the UE's registered PLMN is not allowed to operate in the present UE location.
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4.2.2.3.2  UE-initiated Deregistrationp. 54
The UE uses this procedure to deregister from the registered PLMN as shown in Figure 4.2.2.3.2-1.
Reproduction of 3GPP TS 23.502, Fig. 4.2.2.3.2-1: UE-initiated Deregistration
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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.
Step 2.
[Conditional] AMF to SMF (or V-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 (or V-SMF) for each PDU Session. If the AMF determines that the secondary RAT usage reporting is required for the PDU Session, the AMF shall execute step 7 and 8 and then wait for the completion of step 8 to receive the secondary RAT usage data from the NG-RAN. After that, steps 2 to 6 in this procedure are performed to e.g. release the PDU Session(s).
For home routed roaming case, the V-SMF initiates the release of the PDU Session at the H-SMF by invoking the Nsmf_PDUSession_Release request.
Step 3.
[Conditional] The SMF (or H-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:
Step 3a.
[Conditional] The SMF (or H-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.
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.
Step 4.
[Conditional] The SMF (or V-SMF) responds with Nsmf_PDUSession_ReleaseSMContext Response message.
For home routed roaming case, the H-SMF responds to the V-SMF with a Nsmf_PDUSession_Release response. The V-SMF releases the corresponding User Plane resources. The V-SMF responds to AMF with Nsmf_PDUSession_ReleaseSMContext Response message.
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.
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.
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.
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.
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 Deregistrationp. 55
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 the UE's registered PLMN is not allowed to operate in the present UE location or if a disaster condition is no longer being applicable, the AMF initiates Network-initiated Deregistration to trigger the return of UEs to the PLMN that had a Disaster Condition) or implicit (e.g. expiring of Implicit Deregistration timer). The UDM can trigger this procedure for operator-determined purposes (e.g. if a disaster condition is no longer being applicable as specified in clause 5.40.5 of TS 23.501) to request the removal of a subscriber's RM context and PDU Session(s) of the UE.
Reproduction of 3GPP TS 23.502, Fig. 4.2.2.3.3-1: Network-initiated Deregistration
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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.
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.
For NR satellite access, the AMF initiates Network-initiated Deregistration if it detects that the UE's registered PLMN is not allowed to operate in the present UE location. In this case, the AMF shall provide the appropriate cause value indicating the PLMN is not allowed to operate in the present UE location, see clause 5.4.11.4 of TS 23.501.
If the network de-registration is triggered for a UE registered for Disaster Roaming due to a disaster condition no longer being applicable, the Deregistration Request shall contain the cause value "PLMN not allowed" and include a disaster return wait range as described in clause 5.5.2.3.1 of TS 24.501 and as specified in clause 5.40.5 of TS 23.501, the network, shall organise the return of the Disaster Roaming UEs in a manner that does not cause overload (e.g. of signalling) in the PLMN that previously had the Disaster Condition.
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.
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.
Step 5.
[Conditional] As in step 6 of Figure 4.2.2.3.2-1.
Step 5a.
[Conditional] As in step 6a of Figure 4.2.2.3.2-1.
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.
Step 7.
[Conditional] AMF to AN: N2 UE Context Release Request (Cause): as in step 8 of Figure 4.2.2.3.2-1.
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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