Delta Training-SCP Reprioritization.pptx

scp prioritization

1. SCP Reprioritization in case of Communication Failure (AMF) Delta Training PCC 1.22 Dawei Wan

2. Overview Technical details Operation and maintenance Network impact References Agenda

3. Background: Before this feature, if an SCP down, AMF can reselect another SCP when request fails, but can’t avoid sending requests to the failed SCP. Signal can be wasted and cause long latency. After this feature, if AMF can know SCP is down based on response, AMF will mark the SCP as temporarily unavailable. AMF will down prioritize the SCP in temporarily unavailable state when selecting SCP for the following requests. SCP reselection is also enhanced to save signalling. For error responses indicates the failure of target NF, AMF will not trigger SCP reselection even if the server header indicates the SCP. Benefit: Improves first-time success rate for indirect communication Mode C. Decrease end-to-end latency. Overview

4. AMF supports to mark the SCP as temporarily unavailable when AMF can tell the SCP is down in procedure. AMF supports to prioritize available SCP when selecting SCP. Temporarily unavailable SCP will not be used if there is other available SCP. AMF won’t trigger SCP reselection for error response indicating target NF failure. Overview Supported use case

5. AMF supports to mark the SCP as temporarily unavailable when Receive error response with server header set to the FQDN of the SCP with 429 500 + INSUFFICIENT_RESOURCES 500 + SYSTEM_FAILURE 503 Request timeout HTTP connection to that SCP setup fail When selecting SCP, AMF down prioritize unavailable SCPs, which means when there is available SCP, AMF will not select temporarily unavailable SCP. AMF start a timer for the temporarily unavailable SCP, before the timer expires, AMF will keep the SCP in temporarily unavailable state, except There is successful response or error response indicating failure of other NE from the SCP. The configuration of SCP has changed. After the timer expires, AMF automatically marks the SCP state as available. Technical details 1(3)

6. Technical details 2(3) The request sent via SCP1 fails and the error indicates SCP1 is down. AMF marks SCP1 as temporarily unavailable. And reselect another SCP for the current request. AMF avoids to select SCP1 in following requests when it is marked as temporarily unavailable.

7. SCP reselection is enhanced. AMF now reselects SCP without reselecting NF when: AMF receives error response (status code 400-599) with server header set to the FQDN of the next hop SCP except: 504 + TARGET_NF_NOT_REACHABLE 500 + NF_FAILOVER or NF_SERVICE_FAILOVER Request Timeout HTTP connection setup failure Technical details 3(3)

8. New CLI parameter to config the SCP reprioritization behavior. modify_scp_ne [- erss EnableReprioritizedScpSelection ] [-stud ScpTempUnavailableDuration ] The EnableReprioritizedScpSelection parameter specifies if SCP reprioritization in selection is enabled. The ScpTempUnavailableDuration parameter specifies the duration of the timer which is used to maintain a "temporarily unavailable" status for an SCP instance. This timer will be started for each temporarily unavailable SCP instance. When the timer expires, the status of the temporarily unavailable SCP instance is changed to "available" automatically. The unit of this parameter is second. Example: m odify_scp_ne - erss true -stud 1500 Operation & maintenance CLI

9. New CLI parameter to demonstrate current SCP status. get/ list_scp_instance [-ss ScpStatus ] The read-only parameter ScpStatus specifies the availability status of SCP. The value range is Available/Temporarily Unavailable. Example gsh get_scp_instance -sin scp1 Parameter                       Active Data              Planned Data  ----------------------------------------------------------------------------------- timestamp                        20220428041214           _             planState                         _                        _             fqdn ( Fqdn )                      service.gtt.example.com  _             scheme (Scheme)          http                     _              ap ( ApiPrefix )                  NULL                     _             fpn ( FqdnPortNumber )            NULL                     _             ss ( ScpStatus )                  temporarily_unavailable   _             ssrs ( ScpSelectionRuleSetName )  rule0                     _             ln ( IpEndpointListName )         SCPIpEp1                  _              Operation & maintenance CLI

10. The AMF can now be configured to set the SCP status to the Temporarily Unavailable status for a configurable period in specified cases. An SCP with the Temporarily Unavailable status is given the lowest selection priority for SCP selection. This enhancement helps to save network resources and helps protect against latency issues by preventing request messages from being sent to an unavailable SCP. Network impact

11. Updated CPI documents Indirect Communication for the AMF (TPD) Configure Indirect Communication for the AMF(OPI) SCP (CLI) Parameter Description Packet Core Controller Operational Delta PCC Network Impact Report References