UE Registration Scenario

When UE registers on the network, AMF initiates the UE Policy Create Request to PCF. PCF must respond with a set of policy rules based on the policy logic which takes in to account the status of the UE (SPLMN, Location area) in the network.

UE De-Registration Scenario

If the UE de-register from the network, AMF triggers UE Policy Delete Request of the UE policy to PCF. PCF will delete any Policy Association stored in the database or in the UDR for the subscriber

N1N2 Transfer Failure

Following is the call flow for N1N2 transfer failure:

UE CM-IDLE State

PCF detected the change in UE policy by means of all the use cases while UE is in RM-registered and CM-Connected states.

• Once the PCF sends UE policy in the N1N2 message transfer fails as UE in CM-IDLE state, AMF triggers the event notification that the UE is in CM-IDLE state.

AMF triggers the event notification once the UE is back in the CM connected state. After which, PCF retries the updated policy in N1N2MessageTransfer.

UDR Data-Based UE Policy Update Call Flow

Following is the UE Policy update call flow for UDR notification with SubscCats attribute change.

URSP is pre-configured in the UE or provisioned to UE from PCF. The pre-configured policy is applied by the UE only when it has not received the same type of policy from the PCF.

• PCF selects the UE policy information applicable for each UE based on local configuration, and operator policies.

• PCF provides the UE policy information to the AMF through N15 or Namf interface and then from AMF to the UE through the N1 interface and AMF will not change the UE policy information provided by the PCF.

• PCF adds policy control trigger through Npcf_UEPolicyControl Create Response to AMF.

• The PCF is responsible for delivery of UE policy. If the PCF is notified about UE policy information delivery failure, then PCF will retry based on the configuration.

• If the UE has an URSP rule (except the URSP rule with the match all traffic descriptor) that matches the application as the UE shall perform the association of the application to the corresponding PDU session.

• If no URSP rule is applicable for the application, the UE shall perform the association of the application to a PDU session according to the applicable UE local configurations.

UE Policy Delivery

• PCF provides the UE policy information during UE Policy Association Establishment and UE Policy Association Modification procedures.

• The PCF includes the UE policy information delivered to the UE into a Policy Section identified by a Policy Section Identifier (PSI).

• The PCF may divide the UE policy information into different Policy Sections, each one identified by a PSI. Each policy section provides a list of self-contained UE policy information to the UE, through AMF. The PCF ensures that a policy section is under a predefined size limit, known by the PCF.

• The size limit is configured in the PCF. The PLMN ID is provided to the UE together with UE policy information and it is used to indicate which PLMN a policy section list belongs to.

• If the UE has no policy sections with the same PSI, the UE stores the policy section.

• If the UE has an existing policy section with the same PSI, the UE replaces the stored policy section with the received information.

• The UE removes the stored policy section if the received information contains only the PSI.

• The UE keeps the received UE policies stored even when registering in another PLMN.

• The UE provides the list of stored PSIs (Policy Section Identifier) which identify the policy sections associated to the home PLMN that are currently stored in the UE.

• The UE may trigger an initial registration with the list of stored PSIs to request a synchronization for example if the UE powers up without USIM being changed.

• If USIM is changed, the UE does not provide any PSI. If no policies are stored in the UE for the home PLMN, the UE does not provide any PSI associated to the home PLMN.

• PCF subscribes to the AMF to be notified about the UE response to an update of UE policy information.

• PCF invokes Namf_Communication_N1N2MessageTransfer service operation then AMF shall transfer transparently the UE Policy to UE.

• After the successful N1Message Notification from AMF, UE Policy gets installed in the UE. So PCF will send the UDR update message with the installed UE Policy details.

• When UE is not reachable AMF reports to the PCF that the UE Policy could not be delivered to the UE using Namf_Communication_N1N2TransferFailureNotification.

Principles of PTI Handling For UE Policy Delivery Service Procedures

When the PCF or the UE initiates a procedure, it shall include a valid PTI value in the message header of the command message or the request message.

When the PCF initiates a transaction related procedure, it shall include a valid PTI value in the message header of the command message.

If a response message is sent as a result of a received command or request message, the UE or the PCF shall include in the response message the PTI value received within the received command or request message.

If a command message is sent as a result of a received request message, the PCF shall include in the command message the PTI value received with the request message.

To initiate the network-requested UE policy management procedure, the PCF shall:

• Allocate a PTI value currently not used and set the PTI IE to the allocated PTI value.

• Encode the information about the UE policy sections to be added, modified, or deleted in a UE policy section management list IE as specified in subclause D.6.2 and include it in a MANAGE UE POLICY COMMAND message.

• Send the MANAGE UE POLICY COMMAND message to the UE via the AMF .

• Start the timer T3501.

Note	The PCF starts a different timer T3501 for each allocated PTI value.

UPSI Handling by UE

PCF Processes the UPSI (UE Policy Section Identifier) from UE Policy association request to identify the delta and re-install the delta of UE Polices.

Upon receipt of the MANAGE UE POLICY COMMAND message with an unsed PTI value, the UE shall:

• Store the received UE policy section of the instruction, if the UE has no stored UE policy section associated with the same UPSI as the UPSI associated with the instruction.

• Replace the stored UE policy section with the received UE policy section of the instruction, if the UE has a stored UE policy section associated with the same UPSI as the UPSI associated with the instruction.

• Delete the stored UE policy section, if the UE has a stored UE policy section associated with the same UPSI as the UPSI associated with the instruction and the UE policy section contents of the instruction is empty.

Network Requested UE Policy Management Procedure Not Accepted by the UE

If the UE could not execute all instructions included in the UE policy section management list IE successfully, the UE shall:

• Set the PTI IE to the PTI value received within the MANAGE UE POLICY COMMAND message and encode the UPSI associated with the instructions which could not be executed successfully. The associated UE policy delivery service cause indicating the cause of the failure in a UE policy section management result IE and include it in a MANAGE UE POLICY COMMAND REJECT message.

• Transport the MANAGE UE POLICY COMMAND REJECT message using the NAS transport procedure. Upon receipt of the MANAGE UE POLICY COMMAND REJECT message, the PCF shall stop timer T3501. Any instruction that was included in the UE policy section management list IE and associated UPSI is not included in a UE policy section management result IE of the received MANAGE UE POLICY COMMAND REJECT message is considered as successfully executed.

The PCF should ensure that the PTI value assigned to this procedure is not released immediately.

UE Policy NAS: UE Initiated UE State Indication Procedure

The purpose of the UE-initiated UE state indication procedure is:

• To deliver the UPSI(s) of the UE policy section(s)

• To indicate whether UE supports ANDSP (Access Network Discovery & Selection Policy).

• To deliver one or more OS Ids of the UE to the PCF.

Note

UE sends state indication to AMF and AMF will initiate UE policy association create/update request with the UE state transferred transparently using uePolReq attribute. PCF compares UE state with the policy decision and determine if policy sections need to add/updated/remove. PCF shall send only the modified policy sections to UE to update the policy using one or more MANAGE UE POLICY command.

UE Initiated UE State Indication Procedure Initiation

To initiate the UE-initiated UE state indication procedure, the UE shall create a UE STATE INDICATION message. The UE:

• Shall allocate an unused PTI value and set the PTI IE to the allocated PTI value.

• If not operating in the SNPN access operation mode, shall include the UPSI of the UE policy section which are identified by a UPSI with the PLMN ID part indicating the HPLMN or the selected PLMN available in the UE in the UPSI list IE.

• Shall specify whether the UE supports the ANDSP in the UE policy class mark IE.

• Includes one or more OS IDs in the UE OS Id IE.

The UE shall send the UE STATE INDICATION message. The UE shall transport the created UE STATE INDICATION message using the registration procedure.

When receiving the UE STATE INDICATION message, the (V-)(H-)PCF shall determine, based on the UPSIs, the ANDSP support indication and the OSId(s) indicated in that message, UPSCs (UE Policy Section Code) stored in the UDR and local policy, whether any new UE policy section(s) need to be installed and whether any existing UE policy section(s) need to be updated or deleted.

The UE policy network class mark is included when the PCF of a PLMN or an SNPN intends to provide the UE with information about the policy aspects of the network.

UE State Indication

The UE STATE INDICATION message is sent by the UE to the PCF to:

• Deliver the UPSI of the UE policy section stored in the UE.

• Indicate whether the UE supports ANDSP.

• Deliver one or more OS Ids of the UE.

Message type: UE STATE INDICATION

Direction: UE to network

AMF Relocation

When AMF relocation UE context transfers from an OLD AMF to a new AMF, the PCF processes the UE Policy Update message from the new AMF and update the UE session.

PCF unsubscribes the N1Message Notification subscription from an old AMF and subscribes the N1Message Notification to a new AMF. Any further UE Policy Delivery happens through a new AMF.

UE Policy Delivery Service Message Type

The purpose of the UE policy section management list information element is to transfer from the PCF to the UE a list of instructions to be performed at the UE for management of UE policy section stored at the UE.

The UE policy section management list information element has a minimum length of 12 octets and a maximum length of 65534 octets.

The value part of the UE policy section management list information element consists of one or several UE policy section management sub lists.

UE Policy Section Management Sublist

Following are the details of UE policy section management sub list:

• Length of UE policy section management sub list (octets d to d+1). This field contains the binary encoding of the length of the UE policy section management sub list in units of octets.

• Mobile country code (MCC) from octet d+2, and bits 4 to 1 of octet d+3.

• Mobile network code (MNC) from bits 8 to 5 of octet d+3, and octet d+4 .

• The coding of this field is the responsibility of each administration, but BCD coding shall be used. The MNC shall consist of 2 or 3 digits. If a network operator decides to use only two digits in the MNC, MNC digit 3 shall be coded as 1111.

The UE policy section management sub list contents consist of one or several instructions.

Instructions:

• Instruction contents length (octets d+5 to d+6) This field contains the binary encoding of the instruction contents length in units of octets.

• UPSC (octets d+7 to d+8) This field contains the binary encoding of the UPSC. The value of the UPSC is set by the PCF.

• UE policy section contents (octets d+9 to k)

The UE policy section contents consist of one or several UE policy parts.

UE policy part contents length (octets q to q+1) . This field contains the binary encoding of the UE policy part contents length in units of octets.

UE policy part type (bits 4 to 1 of octet q+2)

Bits

0 0 0 1 URSP

Bits 8 to 5 of octet q+2 are spare and shall be coded as zero.

UE policy part contents

This field contains a UE policy part encoded as specified in 3GPP TS 24.526 [19] for the UE policy part type field set to URSP or ANDSP and encoded as specified in 3GPP TS 24.588 [19C] for the UE policy part type field set to V2XP (V2X Policy).

UE Policy Section Management Result

The purpose of the UE policy section management result information element is to transfer from the UE to the PCF information about instructions for UE policy section management which the UE could not execute successfully.

The UE policy section management result information element has a minimum length of 12 octets and a maximum length of 65534 octets.

Value part of the UE policy section management result information element (octets 4 to z).

The value part of the UE policy section management result information element consists of one or several UE policy section management sub results.

UE Policy Section Management Sub Result

• Number of results (octet d) - This field contains the binary encoding of number of results included in the UE policy section management sub result.

• MCC, Mobile country code (octet d+1, and bits 4 to 1 of octet d+2).

• MNC, Mobile network code (bits 8 to 5 of octet d+2, and octet d+3) - The coding of this field is the responsibility of each administration, but BCD coding shall be used. The MNC shall consist of 2 or 3 digits. If a network operator decides to use only two digits in the MNC, MNC digit 3 shall be coded as "1111".

• UE policy section management sub result contents (octets d+4 to y) - The contents consist of one or several results.

Result (octet f to f+4)

UPSC (octet f to f+1) - This field contains the binary encoding of the UPSC. The value of the UPSC is set by the PCF.

Failed instruction order (octets f+2 to f+3) - This field contains the binary encoding of the order of the failed instruction in the UE policy section management sublist.

Cause (octet f+4)

Bits

8 7 6 5 4 3 2 1

0 1 1 0 1 1 1 1 Protocol error, unspecified

The receiving entity shall treat any other value as 0110 1111, "protocol error, unspecified".

UPSI List

The UPSI list information element transfers the list of UPSIs from the UE to the PCF. The UPSI list information element has a minimum length of 10 octets and a maximum length of 65532 octets.

UPSI List Information Element

MCC - Mobile country code (octet d+2, and bits 4 to 1 of octet d+3).

MNC - Mobile network code (bits 8 to 5 of octet d+3, and octet d+4). The coding of this field is the responsibility of each administration, but the BCD coding shall be used. The MNC shall consist of 2 or 3 digits. If a network operator decides to use only two digits in the MNC, MNC digit 3 shall be coded as "1111".

UPSC (octets d+5 to d+6) - This field contains the binary encoding of the UPSC. The value of the UPSC is set by the PCF.

UE Policy Association Management Service

• Npcf_UEPolicyControl Create Request - This message is for UE Policy Establishment.

• Npcf_UEPolicyControl Delete Request - Provides means to delete UE Policy Association.

• Npcf_UEPolicyControl Update Request - Provides corresponding policies to the PCF whenever the policy control request trigger is met when AMF is relocated due to UE Mobility.

• Namf_ Communication_N1N2Message N1N2MessageTransfer (UE Specific) - This service operation is used by PCF to transfer N1 and/or N2 information to the UE and/or 5G-AN through the AMF.

• Namf_ Communication_N1N2Message N1N2MessageSubscribe (UE Specific) - This message is used by PCF to subscribe to the AMF for notifying N1 messages of a specific type or N2 information of a specific type.

• Namf_ Communication_ N1MessageNotify - This N1MessageNotify service operation is invoked by the AMF, towards the PCF which subscribed to be notified with UPDP messages received from the UE.

• Namf_ Communication_N1N2MessageUnSubscribe - This service operation is used by PCF to unsubscribe to the AMF to stop notifying N1 messages of a specific type .

• Namf_ Communication_N1N2Message N1N2TransferFailureNotification (UE Specific) - This notification to inform PCF that an earlier Namf_Communication_N1N2Message Transfer failed, since AMF failed to deliver the N1 message to the UE as the UE failed to respond to paging.

UDR Query APIs

Following are the APIs for UDR query UEPolicySet:

• GET - Retriver the policy data set for a subscriber.

• PATCH - Modify the policy data set for a subscriber.

UE Policy Association Creation

UE Policy Association create request will be triggered by AMF in following scenarios:

• UE initial registration with the network.

• UE registration with 5GS when the UE moves from EPS to 5GS and there is no existing UE Policy Association between AMF and PCF for this UE.

The AMF creates the UE policy association with the PCF when a UE policy is received from the UE.

The AMF sends a Npcf_UEPolicyControl Create Request with SUPI, may include Access Type and RAT, PEI (Permanent Equipment Identifier), ULI, UE time zone, Serving Network (PLMN ID, or PLMN ID and NID), the Internal-Group-ID-list and UE Policy Container (the list of stored PSIs, operating system identifier).

PCF gets policy subscription related information and the latest list of PSIs from the UDR using Nudr_DM_Query service operation (SUPI, Policy Data, UE context policy control data, Policy Set Entry)

Then PCF sends a Npcf_UEPolicyControl Create Response to the AMF. The PCF relays the Policy Control Request Trigger parameters in the Npcf_UEPolicyControl Create Response.

To establish a UE policy association with the PCF, AMF request with {apiRoot}/npcf-ue-policy-control/v1/policies as Resource URI and the PolicyAssociationRequest data structure as request body shall include the following attributes:

• Notification URI as notificationUri attribute

• SUPI as supi attribute

• Features supported by the NF service consumer as suppFeat attribute

Following are the optional attributes:

• GPSI as gpsi attribute.

• Access type as accessType attribute

• Permanent Equipment Identifier (PEI) as pei attribute

• User Location Information as userLoc attribute

• UE Time Zone as timeZone attribute

• Identifier of the serving network (the PLMN Identifier or the SNPN Identifier), as servingPlmn attribute

• RAT type as ratType attribute

{
  "notificationUri": "string",
  "altNotifIpv4Addrs": [
    "string"
  ],
  "altNotifIpv6Addrs": [
    "string"
  ],
  "altNotifFqdns": [
    "string"
  ],
  "supi": "string",
  "gpsi": "string",
  "accessType": "string",
  "pei": "string",
  "userLoc": "string",
  "timeZone": "string",
  "servingPlmn": "string",
  "ratType": "string" [
    "string"
  ],
  
  "suppFeat": "string"
}

Following is the response body:

• The negotiated supported features are encoded as a suppFeat attribute.

• The information provided by the NF service consumer when requesting the creation of this policy association encoded as a request attribute.

• Following Policy Control Request Trigger are encoded as the triggersattribute:

  • Location change (tracking area)

  • Change of UE presence in PRA

  • Change of PLMN, if the PlmnChange feature is supported.

  • Change of UE connectivity state, if the ConnectivityStateChange feature is supported.

Note	Supports only the PlmnChange and Connectivity Change feature numbers.

UDR GET QUERY

As a part of UE policy association creation and modification request, PCF makes UDR GET request to get UDR profile for the subscriber on ue-policy-set URI.

The response for UDR Get request on UE Policy set has upsi list and urPolicySections, pei, osIds.

As a part of UE Policy Association create request, PCF subscribes to the UDR on any changes of UE Policy Set for the subscriber.

PCF requests notifications from the UDR on changes in the policy data subscription information, and in this case, the PCF shall invoke the Nudr_DataRepository_Subscribe service operation by sending an HTTP POST request to the PolicyDataSubscriptions resource (/policy-data/subs-to-notify/{subsId}).

N1 N2 Message Subscribe and Unsubscribe

To subscribe to notifications of N1 message for UE Policy Delivery Result, or subsequent UE policy requests, the PCF invokes Namf_Communication_N1N2MessageSubscribe service operation to the AMF by sending the HTTP POST method with the URI of the N1N2 Subscriptions Collection for Individual UE Contexts resource.

This subscribe request has ueContextId, n2NotifyCallBackUri and n1MessageClass (UPDP) attributes provided by the PCF.

UE Policy Association Termination

The following cases are considered for UE Policy Association Termination:

• UE Deregistration from the network.

• The mobility with change of AMF .

• 5GS to EPS mobility with N26 if the UE is not connected to the 5GC over a non-3GPP access in the same PLMN.

UE Policy Association Modification Initiated by the AMF

• When the AMF detects a Policy Control Request Trigger condition, then it invokes the Npcf_UEPolicyControl_Update service operation to the PCF by sending an HTTP POST request to the Individual UE Policy Association resource.

• The AMF sends a Npcf_UEPolicyControl Update Request with the following information:

  • UE Policy Association ID associated with the SUPI

  • Policy Control Request Trigger

• PCF sends a Npcf_UEPolicyControl Update Response to the AMF.

• If the PCF decides to update the UE policy that got delivered to UE, the PCF maintains the latest list of UE policy information delivered to the UE and updates the UE policy including the latest list of UPSIs and its content in the UDR by invoking the Nudr_DataRepository_Update service operation. The PCF sends an HTTP PUT or PATCH request to the UEPolicySet resource.

Note	Supports only the PlmnChange and Connectivity Change feature numbers.

AMF requests the update of the associated UE Policy Association by providing the relevant parameters about the UE context in an HTTP POST request with {apiRoot}/npcf-ue-policy-control/v1/policies/{polAssoId}/update as a Resource URI and the PolicyAssociationUpdateRequest data structure as the request body that shall include:

• A new Notification URI encoded in the notificationUri attribute (in case of AMF relocation).

• Observed Policy Control Request Triggers is encoded as triggers attribute.

• If a UE location change occurrs, the UE location is encoded as an userLoc attribute.

• If a MANAGE UE POLICY COMPLETE message or a MANAGE UE POLICY COMMAND REJECT message of the UE policy delivery result, and at least parts of the contents relate to the UPSIs of the HPLMN, the parts of that message that relate to UPSIs of the HPLMN is encoded as the uePolDelResult attribute.

• If a UE PLMN change occurrs and the PlmnChange feature is supported, the PLMN Identifier of the new serving network is encoded as plmnId attribute.

PCF shall determine the applicable UE policy based on the UE Policy Sections stored in the UDR.

If the PCF determines that the UE policy needs to be updated, it shall use the Namf_Communication service to provision the UE policy.

PCF shall send the determined UE policy using the Namf_Communication_N1N2MessageTransfer service operation.

A Policy Update data structure with only mandatory attribute is included in the 200 OK response when the PCF decides not to update the policies.

Discover AMF Interface

The following sample configurations helps to discover the AMF interface:

profile nf-pair nf-type AMF
nrf-discovery-group    nrf-discovery-group
subscription-enabled   true
subscription-extension 5
locality client  loc1
locality preferred-server loc1
locality geo-server geoLocality
Exit

Use the below show command to display the list of profiles:

show rest-endpoint discovered-profiles

PCF stores the AMF attributes such as instanceId, PlmnId and NetworkId to create the AMF set. The PCF uses AMF endpoints while retrying to send the failed N1N1 Messages.

Ops Center Configuration

• By default, PCF skips the following device managers:

  • RX_TGPP

  • SY_V11

  • GX_TGPP

  • N36_TGPP

  • N1N2_TGPP

  • UE_TGPP

  Following is an example to override the skipped device managers that are required for URSP:

  
  engine pcf-green
     properties skipped.device.mgrs
       value RX_TGPP,GX_TGPP,SY_V11
     exit
  exit

• Use the following configuration details for ops center:

  n1n2message.transfer.retry.interval.in.secs

• After the N1 message failure notification, PCF will retry after the configured interval using the following configuration:

  n1n2message.transfer.retry.times

• Use the following configuration to know the number of retry of the N1N2 message transfer after the failure or un-acknowledged status from the AMF.

  n1n2message.transfer.ack.timer.in.secs

URSP Table Driven Configuration

PCF shall determine and evaluate the Table Driven URSP configuration and derive the UE policy.

The PB dervives the UEGroup based on the SubscCats category and SUPI. Further, it uses the UEGroup to derive the PLMNs and UPSCs. Each UPSC contains a list of Traffic Descriptors and Route Selection Descriptors.

Below are the CRD tables:

Input: SubscCats, Subscriber_Id

Output: UEGroup

On receiving the UDR notification, PCF compares the existing SubscCats attribute value with the current attribute value and re-evaluates the Table Driven URSP Configuration, if any delta exists and deliver to the UE through N1N2Message.

TableDrivenUEPolicySectionCode:

Input: UE_Group

Output: PLMN, UPSC

TableDrivenUrspRule:

Input: PLMN, UPSC

Output: Rule_Precedence, TD_RefId, RSD_RefId

Note	Multiple URSP rules in the URSP shall not have the same precedence value.

TableDrivenUrspTrafficDescriptor:

Input: TD​_RefId

Output: TD_Type, TD_Value

Note	List of ENUMs and their format: TD_Types: DNN, OS_ID_APP_ID, MATCH_ALL TD_Value format for type OS_ID_APP_ID: “OS-Id:Application-Id”

TableDrivenUrspRouteSelectionDescriptor:

Input: RSD​_RefId

Output: Precedence, RSD components

Note

List of ENUMs and their format: pduSessType: IPV4, IPV6, IPV4V6 Access_TypePref:_3GPPor NON_3GPP SSC_MODE: SSC_1, SSC_2, SSC_3 SliceInfo value format: SST:SD or SST Non-seamless​_Offload: True or False Each consisting of a precedence value of the route selection descriptor and either: one PDU session type and, optionally, one or more DNN, SliceInfo, AccessTypePref, SSC_Mode non-seamless non-3GPP offload indication

URSP Service Configuration