Protocol Data Unit RAN Tunnel Endpoint Identifier Session

This chapter covers the following topics:

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	Not Applicable
Related Changes in this Release	Not Applicable
Related Documentation	Not Applicable

Revision History

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

Feature Description

The SMF supports activation and deactivation of the user plane connection of a PDU session.

How it Works

Labels are introduced at SMF-service to account active-to-idle and idle-to-active transitions. Existing idle and connected counters are used to track number of PDU sessions that are currently active or idle.


Label	Description
PROCEDURE TYPE	New label introduced. ue_req_active_to_idle ue_req_idle_to_active

Deactivation of the User Plane Connection of a PDU Session

This procedure is used to release the logical NG-AP signaling connection and the associated N3 user plane connections, and (R)AN RRC signaling and resources.

The following reasons may trigger the initiation of AN release:

(R)AN-initiated with cause. For example, O&M Intervention, unspecified failure. (R)AN (For example, Radio) link failure, user inactivity, inter-system redirection, request for establishment of QoS flow for IMS voice, release due to UE generated signaling connection release, mobility restriction and so on.
AMF-initiated with cause. For example, unspecified failure.

Limitations

In this release, SMF supports only UE-initiated deactivation.
Location update is not supported.

Call Flow

Table 3. Deactivation of the User Plane Connection of a PDU Session Call Flow Description

Step

Description

NF Service Consumer requests the SMF to deactivate the user plane connection of the PDU session by sending a POST request with the following information:

upCnxState attribute set to DEACTIVATED.
User location and user location timestamp.
Cause of the user plane deactivation. The cause may indicate a cause received from the 5G-AN or due to an AMF internal event.
Other information (if required).

SMF deactivates and releases the N3 tunnel of the PDU session after receiving such a request. SMF initiates PFCP session modification procedure towards UPF with downlink FAR updated with the following options:

Buffering Action is enabled without remote node “forwarding parameters” details like IP address and GTP-U F-TEID.

Note

NOCP (Notify the CP function) is not enabled. Support for notification is not available on SMF.

SMF sets the upCnxState attribute to DEACTIVATED for the PDU session after receiving successful response from UPF node.

SMF initiates 200 OK response including the upCnxState attribute set to DEACTIVATED towards AMF.

Activation of the User Plane Connection of a PDU Session

The service request procedure is used when the UE is in CM-IDLE and in CM CONNECTED to activate a user plane connection for an established PDU session. The UE in CM IDLE state initiates the service request procedure to send uplink signaling messages, user data or as a response to a network paging request.

Limitations

In this release, SMF supports only UE-initiated service requests.
Paging and network-initiated service requests are not supported.
Location update and access-type changes are not supported.
QoS flow modifications and errors are not supported.

Call Flow

Table 4. Activation of the User Plane Connection of a PDU Session Call Flow Description
Step	Description
1	AMF requests the SMF to activate the user plane connection of the PDU session by sending a POST request with the following information: upCnxState attribute set to ACTIVATING. User location, user location timestamp, and access type associated to the PDU session (if modified) Other information (if required).
2	SMF starts activating the N3 tunnel of the PDU session after receiving the request. SMF returns a 200 OK response including the following information: upCnxState attribute set to ACTIVATING. N2 SM information to request the 5G-AN to assign resources to the PDU session including the transport layer address and tunnel endpoint of the uplink termination point for the user plane data for this PDU session that is UPF's GTP-U F-TEID for uplink traffic.
3	AMF requests the SMF by sending POST request, with the following information: SM information received from the 5G-AN, including the transport layer address and tunnel endpoint of the downlink termination point for the user data for this PDU session, 5G-AN's GTP-U F-TEID for downlink traffic if the 5G-AN succeeded in establishing resources for the PDU sessions.
4	SMF initiates PFCP session modification procedure towards UPF with down link FAR updated with following options: Forwarding Action is enabled with remote node “forwarding parameters” details like IP address and GTP-U F-TEID.
5	SMF sets the upCnxState attribute to ACTIVATED for the PDU session after receiving successful response from UPF node.
6	SMF initiates 200 OK response including the upCnxState attribute set to ACTIVATED towards AMF.

Always-On PDU Session Support

Feature Description

Some applications like the IP Multimedia Subsystem (IMS) require an always-on Protocol Data Unit (PDU) session that the User Plane resource establishes for every transition from the 5GMM-IDLE mode to the 5GMM-CONNECTED mode. The UE requests the establishment of a PDU session as an always-on PDU session based on the request indication of the upper layers. It is the network that decides whether to establish a PDU session as an always-on PDU session.

How it Works

Call Flows

This section includes the following call flows.

PDU Session Establishment Call Flow

This section describes the call flow of the PDU session establishment.

Table 5. PDU Session Establishment Call Flow Description
Step	Description
1	If the UE requests to establish an always-on PDU session, the UE includes an ‘Always-on PDU Session Requested’ IE in the PDU Session Establishment Request message.
2	The SMF checks the DNN profile to determine whether the “always-on” support is enabled.
3	The SMF includes an ‘Always-on PDU Session Indication’ in the PDU Session Establishment Accept message if any one of the following is true: 'Always-on PDU Session Indication' is sent with value as "enabled" if the always-on configuration is enabled under the DNN profile. 'Always-on PDU Session Indication' is sent with value as "disabled" when 'Always-on PDU Session Request' IE is received and configuration is disabled.
4	The SMF does not include an ‘Always-on PDU Session Indication’ only when both these conditions are true: If the UE did not send an ‘Always-on PDU Session Requested’ IE If always-on configuration is disabled in the DNN profile.

UE-Requested PDU Session Modification Call Flow

This section describes the call flow of the UE-requested PDU session modification.

Table 6. UE-Requested PDU Session Modification Call Flow Description

Step

Description

The UE sends an ‘Always-on PDU Session Requested’ IE in the PDU Session Modification Request message.

The SMF checks the DNN profile to determine whether the “always-on” support is enabled.

The SMF includes an ‘Always-on PDU Session Indication’ in the PDU Session Modification Command when any one of the following is true:

'Always-on PDU Session Indication' is sent with the value as "enabled" when the always-on configuration is enabled under the DNN profile.
'Always-on PDU Session Indication' is sent with the value as "disabled" when an 'Always-on PDU Session Request' IE is received and configuration is disabled.

The SMF does not include an ‘Always-on PDU Session Indication’ only when both these conditions are true:

If the UE did not send an ‘Always-on PDU Session Requested’ IE.
If always-on configuration is disabled in the DNN profile.

Note

As per specification 23502, for a PDU session that was established in the EPS, when the UE moves from EPS to 5GS for the first time, the UE includes an 'Always-on PDU Session Requested' indication in the PDU Session Modification Request message if it wants to change the PDU session to an "always-on" PDU session.

Network-Requested PDU Session Modification Call Flow

This section describes the call flow of the network-requested PDU session modification.

Table 7. Network-Requested PDU Session Modification Call Flow Description
Step	Description
1	The SMF decides to trigger a PDU Session Modification due to PCF, UDM, or RAN initiated procedures.
2	The SMF checks the DNN profile to determine whether the “always-on” support is enabled.
3	The SMF determines whether the current DNN configuration for “always-on” is different from the last indication sent to UE. If it differs, the SMF includes an ‘Always-on PDU Session Indication’ IE in the PDU Session Modification Command message.

Configuring Always-On PDU Session Support

To configure always-on PDU session support under the DNN profile, use the following commands:

configure 
   profile dnn name 
   always-on { true | false } 
   end

always-on { true | false } : Enables or disables the "always-on" PDU session support.
- true : Enables always-on PDU session support.
- false : Disables always-on PDU session support.

Verifying Always-On PDU Session Support

Use the show subscriber supi supi_id CLI command to verify the always-on PDU session support.

Note

The show output for always-on PDU session support displays any one of the following options:

“alwaysOn”: “UE Requested”
“alwaysOn”: “Enabled”
“alwaysOn”: “UE Requested & Enabled”

The following is a sample output of the command:

show subscriber supi imsi-123456789012345
subscriber-details
{
  "status": true,
  "genericInfo": {
    "supi": "imsi-123456789012345",
    "pei": "imei-123456786666660",
    "pduSessionId": 5,
    "pduSesstype": "Ipv4PduSession",
   "accessType": "ACCESS_5G",
    "dnn": "intershat",
    "plmnId": {
      "mcc": "123",
      "mnc": "456"
    },
    "sScMode": 1,
    "uetimeZone": "UTC+12:00",
    "allocatedIp": "12.0.4.4",
    "nrLocation": {
      "ncgi": {
        "mcc": "123",
        "mnc": "456",
        "nrCellId": "123456789"
      },
      "tai": {
        "mcc": "123",
        "mnc": "456",
        "tac": "1820"
      }
    }
    “alwaysOn”:  “UE Requested”
  },
  "accessSubData": {
    "amfID": "AFbe08",
    "amfPlmnId": {
      "mcc": "123",
      "mnc": "456"
    },
    "ueCmStatus": "UeCMConnected",
    "amfNrfID": "76517361-338e-4d77-bc76-713a79779574"
  },
  "policySubData": {
    "TotalDynamicRules": 1,
    "TotalFlowCount": 1,
    "TotalNonGBRFlows": 1,
    "pccRuleList": [
      {
        "pccRuleId": "defaultrule",
        "qfi": 1,
        "mbrDl": 125000000,
        "mbrUl": 100000000,
        "flowInformation": [
          {
            "flowDirection": 3,
            "flowDescription": "permit out ip from any to any"
          }
        ]
      }
    ],
    "qosFlow": [
      {
        "qfi": 1,
        "GBRFlow": "False",
        "bindingParameters": {
          "x5Qi": 5,
          "arp": {
            "preemptCap": 1,
            "preemptVuln": 1,
            "priorityLevel": 15
          },
          "priorityLevel": 1
        },
        "AggregatedULMFbr": 100000000,
        "AggregatedDLMFbr": 125000000,
        "pccRuleList": "defaultrule"
      }
    ]
  },
  "chargingData": {},
  "upfServData": {
    "numberOfTunnels": 1,
    "smfSeid": 21790984727,
    "UPState": "Activated",
    "mapping": {
      "tunnelMapping": [
        {
          "TunnelID": 1,
          "tunnelName": "gnbTunnel"
        }
      ]
    }
  }
}

Bulk Statistics for Always-On PDU Session Support

The following statistics are introduced for the Always-On PDU Session Support feature.

Table 8. Bulk Statistics for Always-On PDU Session Support
Bulk Statistics	Description
always-on-pdu	Tracks the number of always-on PDU sessions.
Always-on-pdu-requested	Requests the always-on PDU session.
always-on-pdu-accepted	Accepts the always-on PDU session request.
Always-on-pdu-rejected	Rejects the always-on PDU session request.
pdusetup_req_alwayson_requested	Indicates the number of session establishment requests received with 'Always-On PDU Session Requested'.
pdusetup_acc_alwayson_allowed	Indicates the number of session establishment accept messages sent with the 'Always-On PDU Session Indication enabled.
pdusetup_acc_alwayson_not_allowed	Indicates that the number of session establishment accept messages sent with the 'Always-On PDU Session Indication' disabled.
pdumod_req_alwayson_requested	Indicates the number of session modification requests received with 'Always-On PDU Session Requested'.
pdumod_cmd_alwayson_allowed	Indicates the number of session modification commands sent with the 'Always-On PDU session indication' enabled.
pdumod_cmd_alwayson_not_allowed	Indicates the number of session modification commands sent with the 'Always-On PDU session indication' disabled.
pdumod_cmd_nw_init_alwayson_allowed	Indicates the number of network initiated session modification commands sent with the 'Always-On PDU session indication' enabled.
smf_session_counters	Indicates that the gauge updated to show the number of active always-on pdu sessions.

Ultra Cloud Core 5G Session Management Function, Release 2020.02 - Configuration and Administration Guide

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Ultra Cloud Core 5G Session Management Function, Release 2020.02 - Configuration and Administration Guide

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