UPF Path Management and Restoration

Feature Summary and Revision History

Summary Data

Table 1. Summary Data

Applicable Product(s) or Functional Area

SMF

Applicable Platform(s)

SMI

Feature Default Setting

Disabled – Configuration Required

Related Changes in this Release

Not Applicable

Related Documentation

Not Applicable

Revision History

Table 2. Revision History
Revision Details Release
First introduced. 2020.02.0

Feature Description

A heartbeat is used to monitor the status of a UPF node in terms of its responsiveness. The heartbeat initiates a bilateral flow of request and response between the SMF and UPF.

The SMF periodically sends a signal in the form of a heartbeat request to the registered UPF node to determine if it is active. If the SMF does not receive a response from UPF after the retransmission attempts are exhausted, then SMF recognizes that a failure has occurred and purges the subscribers that are mapped to that UPF node.

You can control the number of heartbeat requests that SMF sends to UPF, the interval between the consecutive requests, and the duration until which SMF waits for a response.

Standards Compliance

The heartbeat transmission between SMF and UPF complies with the following standards:

  • 3GPP TS 23.527

  • 3GPP TS 23.007

Converged Core Refactoring Changes

This section describes the changes related to converged core refactoring in this chapter.

The existing PFCP endpoint configuration is extended to support the "sxa" interface at the interface-level.

How it Works

You can configure the heartbeat capability at the interface-level, UPF profile group-level, or both. The interface-level configuration is mandatory. If the interface-level configuration is unavailable, then the heartbeat parameters get configured with the default values. The profile-level configuration overrides the interface-level configuration.

The heartbeat feature is also extended to achieve high-availability for the Node Manager.

Interface and profile-level heartbeat

The SMF-UPF interaction to detect the UPF path failure using the heartbeat messages involves the following steps:

  1. The SMF sends a heartbeat request message to the discovered UPF instances or profile groups based on the configured schedule.

  2. If the UPF instance or profile is alive, it sends a heartbeat response to the SMF indicating that it is operational. In case the UPF does not send a heartbeat response, then SMF retransmits the heartbeat request based on the configured interval and the number of permitted attempts.

  3. After the configured count of heartbeat message reattempts is exhausted and the SMF does not receive a response from UPF, then SMF starts 'Network requested PDU Session Release' procedure for the subscribers that are associated with that UPF.

Heartbeat and high-availability in Node Manager

Each UPF instance is associated with a primary and secondary Node Manager. The secondary Node Manager acts as a standby system on which the primary manager fails over. The primary Node Manager is responsible for the IP allocation and managing the association-specific messages such as association create, update, or delete request. To achieve uninterrupted access to the UPF and ensure a high-availability environment, the following interactions occur:

  • When the Node Manager goes down or reinstated, it updates its status to all the mapped UPFs.

  • In case the primary Node Manager is down, the secondary manager is notified. The secondary manager sends a heartbeat request to the UPF node to determine if the node is alive.

  • When the secondary Node Manager is informed that the primary Node Manager is available, the secondary manager suspends the heartbeat timers and retransmission for the UPF node that is managed by the primary Node Manager.

Configuration Support for UPF Path Management and Restoration

This section describes how to configure the support for monitoring the UPF status.

Configuring the support for detecting the UPF status using the heartbeat feature involves the following steps:

  • Configuring the Heartbeat Parameters for UPF

  • Configuring the Heartbeat Parameters for UPF Profile

  • Associating UPF Group to Individual UPF Network Configuration

Configuring the Heartbeat Parameters for UPF

This section describes how to configure the heartbeat feature for UPF.

To configure the heartbeat feature for UPF at the interface-level, use the following configuration:

config 

      endpoint pfcp 
         interface { n4 | sxa } 
            heartbeat 
               interval interval 
               max-retransmissions max_retry_count 
               retransmission-timeout retry_interval 
               end

NOTES:

  • endpoint pfcp : Enters the endpoint configuration mode.

  • interface : Configures the N4 or Sxa interface over which the heartbeat messages are exchanged between SMF and UPF.

  • heartbeat : Enters the heartbeat configuration.

  • interval interval : Specify the heartbeat interval in seconds. The accepted range is 60–360. The default value is 60 seconds.

    Setting the interval to "0" disables the heartbeat feature.

  • max-retransmissions max_retry_count : Specify the maximum retries for the Packet Forwarding Control Protocol (PFCP) heartbeat request. The accepted range is 0–10. The default value is 3.

  • retransmission-timeout retry_interval : Specify the heartbeat retransmission timeout in seconds. The accepted range is 1–20. The default value is 5.

Verifying the Heartbeat Configuration for UPF

This section describes how to verify the heartbeat configuration for UPF.

To view the configuration, use the show running-config endpoint pfcp command.

The following is a sample output of the show running-config endpoint pfcp command. 

show running-config endpoint pfcp

 endpoint pfcp
 interface n4
   heartbeat
    interval               61
    retransmission-timeout 3
    max-retransmissions    5
    exit
   exit

interface sxa
  heartbeat
   interval               300
   retransmission-timeout 15
   max-retransmissions    0
   exit
  exit
exit

Configuring the Heartbeat Parameters for the UPF Profile

This section describes how to configure the heartbeat feature for the UPF profile.

To configure the heartbeat parameters for the UPF profile, use the following configuration:
configure 
   profile upf-group group_name 
     heartbeat 
       interval interval 
       retransmission-timeout max_retry  
       max-retransmissions retry_count  
       end

NOTES:

  • profile upf-group group_name — Specifies the UPF group for which the heartbeat feature must be enabled.

  • interface — Configures the N4 interface over which the heartbeat messages are exchanged between SMF and UPF.

  • heartbeat — Enters the heartbeat configuration.

  • interval interval — Specifies the heartbeat interval in seconds. The accepted range is 60–360. The default value is 60 seconds.

    Setting the interval to "0", disables the heartbeat feature.

  • max-retransmissions max_retry — Specifies the maximum retries for the Packet Forwarding Control Protocol (PFCP) heartbeat request. The accepted range is 0–10. The default value is 3.

  • retransmission-timeout retry_count — Specifies the heartbeat retransmission timeout in seconds. The accepted range is 1–20. The default value is 5.

Verifying the Heartbeat Configuration for UPF Group

This section describes how to verify the heartbeat configuration for the UPF group.

To view the configuration, use the show running-config profile upf-group command.

The following is a sample output of the show running-config profile upf-group command.
show running-config profile upf-group
profile upf-group upfGroup1
heartbeat
  interval               62
  retransmission-timeout 3
  max-retransmissions    2
exit
exit

Associating UPF Group to Individual UPF Network Configuration

This section describes how to associate a UPF group with a UPF configuration.

Each UPF network configuration includes the UPF profile that associates each UPF instance with a UPF profile.

To associate an UPF group profile with a network configuration, use the following sample configuration:

config 
   profile network-element upf upf_profile_name 
      upf-group-profile upf_group 
      end

NOTES:

  • profile network-element upf upf_profile_name : Configure the UPF network configuration.

  • upf-group-profile upf_group : Configures the UPF group name that must be associated to the specified UPF network configuration.

Verifying the Association of the UPF Group with the Individual UPF

This section describes how to verify the association of the UPF group with the individual UPF.

To view the association, use the show running-config profile network-element upf command.

The following is a sample output of the show running-config profile network-element upf command. 

profile network-element upf upf1
n4-peer-address ipv4 10.80.70.229
n4-peer-port      8805
upf-group-profile upfGroup1
dnn-list          [ intershat intershat1 intershat2 ]
capacity          65535
priority          65535

OAM Support

This section describes the operations, administration, and maintenance information for this feature.

Bulk Statistics

The SMF maintains the following bulk statistics triggered during the heartbeat request and response procedure.

  • nodemgr_upf_heartbeat_fail_stats— Counter that gets updated per UPF when it fails to respond to a heartbeat request.

  • nodemgr_upf_hb_msg_stats— Counter for all the heartbeat messages for the specified UPF.

    The nodemgr_upf_heartbeat_fail_stats counter supports the following labels:

    • upf_heartbeat_req_tx— Label for the heartbeat request that the SMF sends.

    • upf_heartbeat_req_retx— Label for the retransmitted heartbeat request.

    • upf_heartbeat_rsp_rx— Label for the heartbeat response that the SMF receives.