The SMF supports offline failover for charging when a CHF server fails. When the SMF continues after the CHF server failure, the SMF relays the offline charging services to the offline CHF server.

The offline failover support for the charging feature works as follows.

This section describes how to configure the offline failover support for charging feature.

Configuring the offline failover support for charging feature involves the following steps:

1. Configure failure handling profile in an NF library

2. Configuring an offline server client and an offline failure handling profile

The NF failover support is available in the SMF using the NRF Client profile configuration and the NRF failure profile configuration. The following functionality is supported:

• Configure multiple endpoints for a service as primary and secondary endpoints.

• Specify the failure behavior based on:

  • Message Type

  • HTTP Status Codes in the response messages

The SMF utilizes the NF Failover to achieve the PCF failover support functionality. This section covers working of SMF for message-level failures handling and the corresponding HTTP Status Code-based failure.

The SMF PCF failover supports the following messages that are initiated from the SMF.

• PcfSmpolicycontrolCreate

• PcfSmpolicycontrolUpdate

• PcfSmpolicycontrolDelete

During the PDU session lifecycle, the SMF exchanges the preceding messages at various stages with the PCF. Depending on the HTTP Status code configured in the NRF failure profile, the SMF receives one of the following actions:

• Ignore

• Continue

• Terminate

Note	The messages in Table 1 are SMF-initiated messages.

Use the following configuration to configure the PCF failure handling profile with action config:

profile nf-client-failure nf-type pcf 
 profile failure-handling FH1 
  service name type npcf-smpolicycontrol 
   message type PcfSmpolicycontrolCreate 
    status-code httpv2 0 
     action continue 

Use the following configuration to configure the association of FH profile in the respective network element:

profile network-element pcf pcf1 
 nf-client-profile PP1 
 failure-handling-profile FH1 
 query-params [ dnn ] 
 rulebase-prefix cbn# 
 predefined-rule-prefix crn# 
exit 

Use the following configuration to configure secondary and tertiary IP addresses:

profile nf-client nf-type pcf 
 pcf-profile PP1 
  locality LOC1 
   priority 30 
   service name type npcf-smpolicycontrol 
    endpoint-profile EP1 
     capacity   30 
     uri-scheme http 
     endpoint-name EP1 
      priority 56 
      primary ip-address ipv4 primaryipaddress 
      primary ip-address port 8098 
      secondary ip-address ipv4 secondaryipaddress 
      secondary ip-address port 9098 
      end 

The following statistics are added in support of SMF Failover to Secondary PCF feature.

• PcfSmpolicyControlCreate

  • Number of ignore responses

  • Number of continue responses

  • Number of terminate responses

• PcfSmPolicyControlUpdate

  • Number of ignore responses

  • Number of continue responses

  • Number of terminate responses

• PcfSmpolicyControlDelete

  • Number of ignore responses

  • Number of continue responses

  • Number of terminate responses

• PolicyUpdateNotifyReq

  • Number of accepted requests

  • Number of rejected requests

  • Number of skipped requests

• PolicyDeleteReq

  • Number of accepted requests

  • Number of rejected requests

  • Number of skipped requests

• PolicyUpdateRequest

  • Number of accepted requests

  • Number of rejected requests

  • Number of skipped requests

• Gauge counter for number of subscribers with policy type local/pcf.

During a session, if the User Plane function (UPF) is in congested state, it rejects the Packet Forwarding Control Protocol (PFCP) establishment messages from SMF with a cause code in the response message. To reduce the call loss, SMF retries to send PFCP establishment messages to a different UPF. Then, SMF selects a UPF based on priority (configuration) and capacity (load information from UPF).

The UPF failure handling support on N4 interface feature in SMF introduces a new failure handling template (FHT) profile for PFCP. This profile is associated with the UPF profile in SMF (in network elements).

The FHT template provides flexibility for SMF to fine tune its interactions with UPFs for sessions. It supports SMF to handle the error cause codes in response from UPF for both new and existing sessions. Based on the error cause codes in response from UPF, this feature provides the following configurable actions:

• terminate

• retry-terminate

This section describes how to configure the UPF failure handling on N4 interface feature.

configure 
   profile failure-handling pfcp_name 
      interface pfcp message N4SessionEstablishmentReq 
      cause-code pfcp-entity-in-congestion 
      action retry-terminate max-retry value 
      end 

NOTES:

• profile failure-handling: Specifies the UPF profile that is associated with FHT.

• interface pfcp message {N4SessionEstablishmentReq | N4SessionModificationReq}: Specifies the failure handling for N4SessionEstablishmentReq (for new sessions) and N4SessionModificationReq messages (for existing sessions).

  Note	UPF reselection is not applicable for message type N4SessionModificationReq because the session is already active on a UPF.

• cause-code {pfcp-entity-in-congestion | mandatory-ie-incorrect | mandatory-ie-missing | session-ctx-not-found | system-failure | service-not-supported | no-resource-available | no-response-received | reject}: Specifies the error codes that SMF receives in the failure response message from UPF.

  Note

  The no-response-received cause code is introduced in this feature to identify the scenarios where SMF does not receive any response from UPF. FHT does not support the following cause codes, which are configured with their default behaviour: request-reject-unspecified , cond-ie-missing , invalid-length , invalid-fw-policy , invalid-fteid-alloc-opt , no-established-pfcp-assoc , rule-creation-mod-failure .

  • pfcp-entity-in-congestion: Specifies the cause code when UPF is congested.

  • reject: Specifies the option to handle the cause codes in the failure response message from UPF, which are not configured by using the CLI commands available for this feature.

• action {retry-terminate | terminate}: Specifies the action to perform based on the error cause code received in the failure response message from UPF.

  • retry-terminate: Specifies a retry attempt to an alternate UPF. If the retry attempt fails, the session is terminated.

    Note	If all UPFs are in congested state, call fails even if the action is set to continue.

  • max-retry: Specifies the number of retry attempts to reselect an alternate UPF.

    • Default value: 2

    • Maximum value: 5

Configuring the Failure Profile Association

This section describes how to configure the failure profile association in this feature.

configure 
   profile upf-group upf upf_group_name 
      failure-profile pfcp_name 
      end 

NOTES:

• profile upf-group upf: Specifies the UPF group.

• failure-profile: Specifies the FHT profile for PFCP.

Configuration Matrix

This section describes the configuration options available for N4 Session Establishment Request and N4 Session Modification Request messages in this feature.

This section describes the show command that is supported by the UPF failure handling on N4 interface feature.

show running-config

Use the show running-config command to view the configuration.

The following configuration is a sample output of the show running-config command:

profile network-element upf upf1
       pfcp pfcp-failure-profile pfcp1
node-id      n4-peer-upf1
n4-peer-address ipv4 1.1.1.1
n4-peer-port 0000
keepalive    60
 dnn-list     [ uncarrier.5g ]
capacity     10
priority     1
exit
profile failure-handling pfcp1
 interface pfcp message N4SessionEstablishmentReq
  cause-code pfcp-entity-in-congestion
   action retry-terminate max-retry 2
  exit
 exit
interface pfcp message N4SessionModificationReq
  cause-code mandatory-ie-incorrect
   action terminate
  exit
 exit
exit