8.4 Restoration procedures for AMF failure
23.5273GPP5G SystemRelease 18Restoration proceduresTS
8.4.1 Multicast MBS session (de)activation or update after an AMF failure
8.4.1.1 General
Different NG-RAN nodes may establish shared delivery for the same MBS session via different AMFs of a same AMF set. During the shared delivery establishment:
– each AMF involved in the establishment of shared delivery stores in its multicast MBS session context the RAN-ID of the NG-RAN nodes that have established shared delivery via this AMF, for subsequent signaling related to the multicast MBS Session (Multicast MBS session activation, deactivation or update); and
– the MB-SMF stores in its multicast MBS session context the NF Instance ID of each AMF involved in the establishment of shared delivery to enable subsequent signalling towards these AMFs.
See clause 7.2.1.4 and Table 6.9.1-1 of 3GPP TS 23.247 [12].
The following procedure may be used to enable the MB-SMF to activate, deactivate or update the multicast MBS session, when an AMF of the AMF set through which one or more NG-RAN nodes had established shared delivery has failed with or without restart or is no longer reachable (e.g. due to networking issues, or because it has been de-instantiated from the AMF set).
8.4.1.2 N2 MBS session request distribution with list of NG RAN Node IDs provided by MB-SMF to AMF
During the shared delivery establishment procedure (see clause 7.2.1.4 of 3GPP TS 23.247 [12]), the MB-SMF stores, for each AMF involved in the establishment of shared delivery, the list of NG-RAN Node IDs having shared delivery established through the AMF.
The MB-SMF may then send any multicast MBS session activation, deactivation and update request towards the NG-RAN nodes that established shared delivery as defined in Figure 8.4.1.2-2.
Figure 8.4.1.2-2: Multicast MBS session activation, deactivation or update via an alternative AMF of the AMF set
0. NG RAN1 establishes shared delivery for the multicast MBS session via AMF1. NG RAN2 and NG RAN3 do so via AMF2. MB-SMF stores corresponding information in its MBS session context.
1. AMF2 becomes no longer available/reachable.
2. The MB-SMF needs to activate, deactivate or update the MBS session.
3. The MB-SMF sends an Namf_MBSCommunication_N2MessageTransfer Request to every AMF of the same AMF set that was involved in the establishment of shared delivery, as specified in clauses 7.2.5.2, 7.2.5.3 and 7.2.6 of 3GPP TS 23.247 [12], but with the request further including the list of NG RAN Node IDs known by the MB-SMF to have established shared delivery through the respective AMF. AMF1 distributes the request to the list of NG-RAN nodes received from the MB-SMF, if any, otherwise to the list of the NG-RAN nodes it has stored locally, if any.
NOTE 1: In absence of AMF failures, an NG-RAN node receives requests to activate, deactivate and update the MBS session via the same AMF through which it established shared delivery.
NOTE 2: Including the list of NG RAN Node IDs in every Namf_MBSCommunication_N2MessageTransfer Request, even towards AMFs that are operational, enable to distribute the requests to the NG RAN nodes, even if these AMFs would have restarted and lost their list of NG RAN node IDs beforehand, or if the SCP would need to reselect a different AMF when using indirect communication.
4. If the MB-SMF is not yet aware that AMF2 has failed, it sends an Namf_MBSCommunication N2MessageTransfer Request to AMF2 as described in step 3 and detects that AMF2 is no longer available.
5. The MB-SMF sends an Namf_MBSCommunication_N2MessageTransfer Request to an alternative AMF (AMF1 in this example) of the same AMF set including the list of NG RAN Node IDs known by the MB-SMF to have established shared delivery through the failed AMF (AMF2). AMF1 distributes the request to the list of NG-RAN nodes received from the MB-SMF.
If the MB-SMF is already aware at the start of this procedure that AMF2 has failed, the MB-SMF may already include in step 3 the list of NG RAN Node IDs known by the MB-SMF to have established shared delivery through the failed AMF (AMF2).When using unicast transport over N3mb, the MB-SMF may determine that a NG-RAN node has failed or restarted as specified in clause 8.3.4. In this case, the MB-SMF shall remove this NG RAN node from its MBS session context.
NOTE 3: This avoids that the MB-SMF requests an AMF to send requests to NG RAN nodes that have failed or restarted, i.e. that have no more shared delivery established.
In scenarios where the MB-SMF would request an AMF to distribute an activate, deactivate or update request to a NG RAN node that has no longer shared delivery established (e.g. the NG RAN node has restarted but this has not been detected by the MB-SMF), the NG RAN will return an activation or update failure to the AMF. To enable the MB-SMF to be notified about this failure and to remove the NG RAN node ID from its MBS session context, the MB-SMF shall include a notification URI in every Namf_MBSCommunication_N2MessageTransfer Request it sends and the AMF shall notify a failure received from an NG RAN node towards the MB-SMF by sending an Namf_MBSCommunication_Notify request to the notification URI that was received in the request.
Likewise, if an AMF receives an Namf_MBSCommunication_N2MessageTransfer Request including a NG RAN Node ID and the AMF cannot send any N2 message towards this NG RAN node (e.g. the NG-RAN node has failed without restart), the AMF shall notify the failure to send N2 MBS session requests to the NG RAN node by sending an Namf_MBSCommunication_Notify request to the notification URI that was received in the request.
NOTE 4: When IP multicast is used over N3mb, the MB-SMF cannot detect via the MB-UPF that a NG RAN node has failed or restarted. So in this case, and also possibly even when using unicast transport, it can occur that the MB-SMF requests the AMF to send an activate, deactivate or update request to an NG RAN node that has no longer shared delivery established.
Annex A (informative):
Change history
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Change history |
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Date |
Meeting |
TDoc |
CR |
Rev |
Cat |
Subject/Comment |
New version |
|
2018-07 |
CT4#85bis |
C4-185034 |
Initial Draft and skeleton. |
0.0.2 |
|||
|
2018-07 |
CT4#85bis |
C4-185407 |
N4 Failure and Restart Detection, Restoration procedures for User Plane interfaces N3 and N9 Implementation of C4-185409, C4-185410, C4-185411, C4-185412, C4-185413, C4-185414, C4-185527 |
0.1.0 |
|||
|
2018-08 |
CT4#86 |
C4-186509 |
Implementation of C4-186233, C4-186406, C4-186408, C4-186413, C4-186488 |
0.2.0 |
|||
|
2018-09 |
CT#81 |
CP-182082 |
Presented for Information and approval |
1.0.0 |
|||
|
2018-09 |
CT#81 |
Approved in CT#81 |
15.0.0 |
||||
|
2018-12 |
CT#82 |
CP-183021 |
0003 |
– |
F |
GTP-U Error Indication received from 5G-AN |
15.1.0 |
|
2018-12 |
CT#82 |
CP-183021 |
0004 |
4 |
F |
NF service restart detection by direct signalling between NFs |
15.1.0 |
|
2018-12 |
CT#82 |
CP-183021 |
0006 |
1 |
F |
Restoration Procedure for Intermediate UPF Restart |
15.1.0 |
|
2018-12 |
CT#82 |
CP-183021 |
0007 |
1 |
F |
Restart detection by direct signalling between NFs |
15.1.0 |
|
2018-12 |
CT#82 |
CP-183021 |
0008 |
F |
PWS restoration procedures |
15.1.0 |
|
|
2018-12 |
CT#82 |
CP-183021 |
0009 |
1 |
F |
NF Service Instance Reselection |
15.1.0 |
|
2019-03 |
CT#83 |
CP-190026 |
0010 |
– |
F |
NF Restart detection |
15.2.0 |
|
2019-06 |
CT#84 |
CP-191038 |
0011 |
1 |
F |
Corrections to Restoration procedures |
15.3.0 |
|
2019-06 |
CT#84 |
CP-191044 |
0012 |
2 |
F |
Clarifications on UPF restoration procedure |
16.0.0 |
|
2019-06 |
CT#84 |
CP-191044 |
0013 |
1 |
F |
Clarifications on GTP-U Error Indication received by 5G-AN |
16.0.0 |
|
2019-09 |
CT#85 |
CP-192124 |
0014 |
– |
F |
Regulation of contexts restoration by NFs |
16.1.0 |
|
2019-12 |
CT#86 |
CP-193045 |
0017 |
1 |
F |
PFCP Association Setup Request with same Node ID |
16.2.0 |
|
2019-12 |
CT#86 |
CP-193045 |
0018 |
2 |
F |
Reestablishment of PFCP sessions after a UP function restart |
16.2.0 |
|
2020-06 |
CT#88e |
CP-201030 |
0019 |
2 |
B |
Populating Recovery Information via Direct signalling from a Service Producer |
16.3.0 |
|
2020-06 |
CT#88e |
CP-201030 |
0021 |
2 |
B |
Populating Recovery Information of NF (Service) Set via NRF |
16.3.0 |
|
2020-06 |
CT#88e |
CP-201030 |
0020 |
2 |
B |
Populating Recovery Information via Direct signalling from a Service Consumer |
16.3.0 |
|
2020-06 |
CT#88e |
CP-201030 |
0023 |
– |
F |
NF Service Instance Reselection |
16.3.0 |
|
2020-09 |
CT#89e |
CP-202119 |
0024 |
1 |
F |
Reselection when the Routing Binding Indication unavailable |
16.4.0 |
|
2020-12 |
CT90e |
CP-203054 |
0025 |
1 |
F |
NF reselection by the SCP without Routing Binding Indication |
16.5.0 |
|
2021-03 |
CT#91e |
CP-210032 |
0027 |
– |
F |
Partial failure handling support over N4 |
17.0.0 |
|
2021-06 |
CT#92e |
CP-211059 |
0031 |
1 |
A |
Clarifications to NF service producer reselection procedure (w/o binding support) |
17.1.0 |
|
2021-06 |
CT#92e |
CP-211043 |
0030 |
2 |
B |
Restoration of PFCP sessions affected by a partial or complete failure |
17.1.0 |
|
2021-06 |
CT#92e |
CP-211049 |
0029 |
5 |
B |
I-SMF/V-SMF Restoration procedure |
17.1.0 |
|
2021-12 |
CT#94e |
CP-213086 |
0035 |
– |
F |
Mandating SCPs to support NF reselection for Model C/D delegated discovery |
17.2.0 |
|
2021-12 |
CT#94e |
CP-213122 |
0036 |
1 |
B |
Void I-SMF/V-SMF Restoration procedure from normal specification clause |
17.2.0 |
|
2021-12 |
CT#94e |
CP-213120 |
0037 |
– |
F |
Update the reference |
17.2.0 |
|
2022-03 |
CT#95e |
CP-220035 |
0041 |
1 |
B |
MBS session restoration upon MB-UPF failure with restart |
17.3.0 |
|
2022-03 |
CT#95e |
CP-220035 |
0042 |
1 |
B |
MBS session restoration upon MB-UPF failure without restart |
17.3.0 |
|
2022-03 |
CT#95e |
CP-220036 |
0038 |
3 |
B |
Stage 2 description on Restoration of Profiles related to UDR |
17.3.0 |
|
2022-03 |
CT#95e |
CP-220037 |
0039 |
1 |
B |
Detection and reporting of the restart of a GTP-U entity |
17.3.0 |
|
2022-03 |
CT#95e |
CP-220086 |
0040 |
3 |
B |
Enhanced handling at user plane path failure |
17.3.0 |
|
2022-03 |
Editorial corrections |
17.3.1 |
|||||
|
2022-06 |
CT#96 |
CP-221023 |
0044 |
1 |
F |
Restoration procedure for MB-UPF restart |
17.4.0 |
|
2022-06 |
CT#96 |
CP-221023 |
0048 |
1 |
B |
Restoration of a Broadcast MBS session upon NG-RAN failure with or without restart |
17.4.0 |
|
2022-06 |
CT#96 |
CP-221023 |
0049 |
1 |
B |
Restoration of a Multicast MBS session upon NG-RAN failure with or without restart |
17.4.0 |
|
2022-06 |
CT#96 |
CP-221024 |
0053 |
– |
F |
Removal of Editor’s note for MB-UPF failure without restart |
17.4.0 |
|
2022-06 |
CT#96 |
CP-221024 |
0056 |
1 |
B |
Support of Broadcast MBS Session with an AMF set being deployed |
17.4.0 |
|
2022-06 |
CT#96 |
CP-221025 |
0046 |
3 |
F |
Updates on Stage 2 description on Restoration of Profiles related to UDR |
17.4.0 |
|
2022-06 |
CT#96 |
CP-221045 |
0045 |
1 |
F |
Failure to restore a PFCP session at UPF restart |
17.4.0 |
|
2022-06 |
CT#96 |
CP-221045 |
0054 |
1 |
F |
Target NF type in notification request for NF service consumer reselection by SCP |
17.4.0 |
|
2022-06 |
CT#96 |
CP-221045 |
0055 |
– |
F |
Set Deletion procedure |
17.4.0 |
|
2022-06 |
CT#96 |
CP-221061 |
0057 |
1 |
F |
Restoration procedures for Home Routed PDU Sessions or PDU sessions with an I-SMF |
17.4.0 |
|
2022-06 |
CT#96 |
CP-221061 |
0058 |
1 |
F |
Restoration procedures for Home Routed PDU Sessions or PDU sessions with an I-SMF |
17.4.0 |
|
2022-06 |
Editorial corrections |
17.4.1 |
|||||
|
2022-09 |
CT#97e |
CP-222031 |
0059 |
– |
F |
Corrections to the Broadcast MBS session restoration procedures |
17.5.0 |
|
2022-09 |
CT#97e |
CP-222035 |
0061 |
– |
F |
Updates on Stage 2 description on Restoration of Profiles related to UDR |
17.5.0 |
|
2022-12 |
CT#98e |
CP-223036 |
0062 |
– |
F |
Corrections on ContextStatusNofity event for multicast transport over N19mb |
17.6.0 |
|
2022-12 |
CT#98e |
CP-223036 |
0064 |
2 |
F |
Impact of Shared NG-U Termination on MBS Restoration Procedures |
17.6.0 |
|
2022-12 |
CT#98e |
CP-223087 |
0063 |
– |
B |
Multicast MBS session (de)activation or update after an AMF failure |
18.0.0 |