5.3 Namf_EventExposure Service

29.5183GPP5G SystemAccess and Mobility Management ServicesRelease 16Stage 3TS

5.3.1 Service Description

The AMF may offer this service as a Service Producer to enable an NF to subscribe to event notifications on its own or on behalf of another NF and get notified about an event. The known Service Consumers are NEF, SMF, UDM, NWDAF and LMF. See also clause 5.34.7 of 3GPP TS 23.501 [2] and clauses 4.15.1, 4.15.3.2, 4.15.4.2 and 5.2.2.3.1 of 3GPP TS 23.502 [3], clause 6.2.2 in 3GPP TS 23.288 [38].

The following events are provided by Namf_EventExposure Service:

Event: Location-Report

A NF subscribes to this event to receive the Last Known Location or the Current Location of a UE or a group of UEs or any UE, and Updated Location of any of these UEs when AMF becomes aware of a location change of any of these UEs with the granularity as requested.

This event implements the "Location Reporting" event in table 4.15.3.1-1 of 3GPP TS 23.502 [3].

UE Type: One UE, Group of UEs, any UE

Report Type: One-Time Report, Continuous Report (See NOTE 1), Periodic Report (See NOTE 1 and 2)

Input: UE-ID(s), "ANY_UE", optional filters: TAI, Cell-ID, N3IWF, UE-IP, UDP-PORT, TNAP ID, TWAP ID, Global Line Id

Notification; UE-ID, filtered updated location (TAI, Cell-ID for 3GPP access, most recent N3IWF node, UE local IP address and UDP source port number for non-3GPP access, TNAP ID, TWAP ID, Global Line Id).

NOTE 1: Support of Continuous Report or Periodic Report should be controlled by operator policy.

NOTE 2: For Periodic Report, UE Last Known Location is reported if the UE is in CM-IDLE state when the report is being generated.

Event: Presence-In-AOI-Report

A NF subscribe to this event to receive the current present state of a UE or a group of UEs or any UE in a specific Area of Interest (AOI), and notification when a specified UE enters or leaves the specified area. The area could be identified by a TA list, an area ID or specific interested area name like "LADN".

UE Type: One UE, Group of UEs, any UE

Report Type: One-Time Report, Continuously Report

Input: UE ID(s), "ANY_UE", Area identifier (a TA list, an area Id or "LADN"), S-NSSAI, NSI ID.

Notification: UE-ID(s), Area identifier, Presence Status (IN/OUT/UNKNOWN)

Event: Time-Zone-Report

A NF subscribes to this event to receive the current time zone of a UE or a group of UEs, and updated time zone of the UE or any UE in the group when AMF becomes aware of a time zone change of the UE.

UE Type: One UE, Group of UEs

Report Type: One-Time Report, Continuous Report

Input: UE ID(s)

Notification; UE-ID, most recent time-zone

Event: Access-Type-Report

A NF subscribes to this event to receive the current access type(s) of a UE or a group of UEs or any UE, and updated access type(s) of any of the UEs when AMF becomes aware of the access type change of any of these UEs. The area could be identified by a TA list, an area ID or specific interested area name like "LADN".

UE Type: One UE, Group of UEs, any UE

Report Type: One-Time Report, Continuous Report

Input: UE ID(s), "ANY_UE", optionally filters: Area identifier (a TA list, an area Id or "LADN")

Notification; UE ID, most recent access-types (3GPP, Non-3GPP)

Event: Registration-State-Report

A NF subscribes to this event to receive the current registration state of a UE or a group of UEs or any UE, and report for updated registration state of any of these UEs when AMF becomes aware of a registration state change of any of these UEs. The area could be identified by a TA list, an area ID or specific interested area name like "LADN".

UE Type: One UE, Group of UEs, any UE

Report Type: One-Time Report, Continuous Report

Input: UE ID(s), "ANY_UE", optionally filters: Area identifier (a TA list, an area Id or "LADN")

Notification; UE ID, most recent registration state (REGISTERED/DEREGISTERED) with access type

Event: Connectivity-State-Report

A NF subscribes to this event to receive the current connection management state of a UE or a group of UEs, and report for updated connection management state of a UE or any UE in the group when AMF becomes aware of a connection management state change of the UE.

UE Type: One UE, Group of UEs

Report Type: One-Time Report, Continuous Report

Input: UE ID(s)

Notification; UE ID, most recent connection management state (IDLE/CONNECTED) with access type

Event: Reachability-Report

A NF subscribes to this event for "UE Reachability Status Change" to receive the current reachability state of a UE or a group of UEs in the AMF, and report for updated reachability state of a UE or any UE in the group when AMF becomes aware of a reachability state change of the UEs between REACHABLE, UNREACHABLE, REGULATORY_ONLY. The following conditions apply:

– the AMF shall send a Reachability Report ("UNREACHABLE") if the Mobile Reachable Timer expires (see clause 5.4.1.1 of 3GPP TS 23.501 [2]) or the UE enters CM-IDLE when it is only registered over the Non-3GPP access (see clause 5.5.3 of 3GPP TS 23.501 [2]);

– the AMF shall send a Reachability Report ("REGULATORY_ONLY") if the UE becomes reachable only for regulatory prioritized service (see clause 4.2.3.3 of 3GPP TS 23.501 [2]);

– the AMF shall send a Reachability Report ("REACHABLE") when the UE reachability state changes from any of the two above states to REACHABLE.

NOTE 3: The AMF does not send a Reachability Report ("UNREACHABLE") in particular when the UE enters extended DRX cycle (see clause 5.31.7.2.2.3 of 3GPP TS 23.501 [2]), the UE enters power saving state (see clause 5.31.8 of 3GPP TS 23.501 [2]), the UE enters CM IDLE in MICO mode (see clause 5.4.1.3 of 3GPP TS 23.501 [2]), or when the UE does not respond to a paging request.

An NF subscribes to this event for "UE Reachable for DL Traffic" to receive reports of a UE or a group of UEs when the UE becomes reachable for sending downlink data. In this case, the event is detected when the UE transitions to CM-CONNECTED mode or when the UE will become reachable for paging, as specified in table 4.15.3.1-1, clauses 4.2.5 and 4.3.3 of 3GPP TS 23.502 [3]. When reporting the "UE Reachable for DL Traffic", the AMF shall also indicate the access types through which the UE is reachable.

UE Type: One UE, Group of UEs

Report Type: One-Time Report, Continuous Report

Input: UE ID(s), (optional) Reachability Filter

Notification; UE ID, AMF Id, most recent reachability state (REACHABLE/UNRACHABLE/REGULATORY_ONLY), access type(s) through which the UE is reachable.

Event: Communication-Failure-Report

A NF subscribes to this event to receive the Communication failure report of a UE or group of UEs or any UE, when the AMF becomes aware of a RAN or NAS failure event.

This event implements the "Communication failure" event in table 4.15.3.1-1 of 3GPP TS 23.502 [3].

UE Type: One UE, Group of UEs, any UE

Report Type: One-Time Report, Continuous Report

Input: UE ID(s), "ANY_UE", optionally filters: Area identifier (a TA list, an area Id or "LADN")

Notification; UE ID, RAN/NAS release code.

Event: UEs-In-Area-Report

A NF subscribes to this event to receive the number of UEs in a specific area. A NF may ask AMF for the UEs within the area based on Last Known Location or it may request AMF to actively look for the UEs within the area based on Current Location.

This event implements the "Number of UEs present in a geographical area" event in table 4.15.3.1-1 of 3GPP TS 23.502 [3].

UE Type: any UE

Report Type: One-Time Report (See NOTE 3), Continuous Report (See NOTE 4), Periodic Report (See NOTE 4) Input: Area identified in a TA List

Notification: Number of UEs in the area

NOTE 4: For an Immediate Report, UE Last Known Location is used to count the UEs within the area.

NOTE 5: Support of Continuous Report or Periodic Report should be controlled by operator.

Event: Loss-of-Connectivity

An NF subscribes to this event to receive the event report of a UE or group of UEs when AMF detects that a target UE is no longer reachable for either signalling or user plane communication. Such condition is identified when Mobile Reachable timer expires in the AMF (see 3GPP TS 23.501 [2]), when the UE detaches and when AMF deregisters from UDM for an active UE. If the UE is already not reachable for either signalling or user plane communication when the event is subscribed, the AMF reports the event directly.

This event implements the "Loss of Connectivity" event in table 4.15.3.1-1 of 3GPP TS 23.502 [3].

UE Type: One UE, Group of UEs.

Report Type: One-Time Report, Continuous Report

Input: UE ID(s)

Notification; UE ID.

Event: 5GS-User-State-Report

A NF subscribes to this event to receive the 5GS User State of a UE.

UE Type: One UE

Report Type: One-Time Report

Input: UE ID(s)

Notification; UE ID, 5GS User State

Event: Availability-after-DDN-failure

A NF subscribes to this event to be notified about the Availability of a UE after a DDN failure.

UE Type: One UE, Group of UEs

Report Type: One-Time Report, Continuous Report

Input: UE ID(s)

Notification: UE ID(s)

Event: Type-Allocation-Code-Report

A NF subscribes to this event to receive the TAC of a UE or a group of UEs or any UE.

UE Type: One UE, Group of UEs, any UE

Report Type: One-Time Report, Continuous Report

Input: UE ID(s),"ANY_UE", optionally filters: TAI, Area identifier (a TA list, an area Id or "LADN")

Notification: UE ID(s), TAC(s)

Event: Frequent-Mobility-Registration-Report

A NF subscribes to this event to receive the number of mobility registration during a period for a UE or a group of UEs or any UE.

UE Type: One UE, Group of UEs, any UE

Report Type: One-Time Report, Continuous Report

Input: UE ID(s), expiry time, "ANY_UE", optionally filters: Area identifier (a TA list, an area Id or "LADN")

Notification: UE ID(s), Frequent Registration

5.3.2 Service Operations

5.3.2.1 Introduction

For the Namf_EventExposure service the following service operations are defined:

– Subscribe;

– Unsubscribe;

– Notify.

5.3.2.2 Subscribe

5.3.2.2.1 General

The Service Operation is used by a NF Service Consumer (e.g. NEF) to subscribe to an event(s) for one UE, group of UE(s) or any UE.

5.3.2.2.2 Creation of a subscription

The Subscribe service operation is invoked by a NF Service Consumer, e.g. NEF, towards the AMF, when it needs to create a subscription to monitor at least one event relevant to the AMF. The NF Service Consumer may subscribe to multiple events in a subscription. A subscription may be associated with one UE, a group of UEs or any UE.

The NF Service Consumer shall request to create a new subscription by using HTTP method POST with URI of the subscriptions collection, see clause 6.2.3.2.

The NF Service Consumer shall include the following information in the HTTP message body:

– NF ID, indicates the identity of the network function instance initiating the subscription;

– Subscription Target, indicates the target(s) to be monitored, as one of the following types:

– A specific UE, identified with a SUPI, a PEI or a GPSI;

– A group of UEs, identified with a group identity;

– Any UE, identified by the "anyUE" flag.

– Notification URI, indicates the address to deliver the event notifications generated by the subscription;

– Notification Correlation ID, indicates the correlation identity to be carried in the event notifications generated by the subscription;

– List of events to be subscribed;

– Event Types per event, as specified in clause 5.3.1.

The NF Service Consumer may include the following information in the HTTP message body:

– Immediate Report Flag per event, indicates an immediate report to be generated with current event status;

– Event Trigger, indicates how the events shall be reported (One-time Reporting or Continuously Reporting).

– Maximum Number of Reports, defines the maximum number of reports after which the event subscription ceases to exist;

– Expiry, defines maximum duration after which the event subscription ceases to exist;

– Sampling ratio, defines the random subset of UEs among target UEs, and AMF only report the event(s) related to the selected subset of UEs;

– Periodic Report Flag per event, indicates the report to be generated periodically;

– Repetition Period, defines the period for periodic reporting;

– Event Filter per applicable event, defines further options on how the event shall be reported.

– Reference Id per event, indicates the value of the Reference Id associated with the event to be monitored. If provided, the Reference Id shall be included in the reports triggered by the event.

Figure 5.3.2.2.2-1 Subscribe for Creation

1. The NF Service Consumer shall send a POST request to create a subscription resource in the AMF. The payload body of the POST request shall contain a representation of the individual subscription resource to be created. The request may contain an expiry time, suggested by the NF Service Consumer as a hint, representing the time upto which the subscription is desired to be kept active and the time after which the subscribed event(s) shall stop generating report.

2a. On success, the request is accepted, the AMF shall include a HTTP Location header to provide the location of a newly created resource (subscription) together with the status code 201 indicating the requested resource is created in the response message. If the NF Service Consumer has included more than one events in the event subscription and some of the events are failed to be subscribed, the AMF shall accept the message and provide the successfully subscribed event(s) in AmfEventSubscription. If the NF Service Consumer has included the immediateFlag with value as "true" in the event subscription, the AMF shall include the current status of the events subscribed, if available (e.g. last known location information is included if the subscribed event is LOCATION_REPORT). If the events with immediateFlag set to "true" are subscribed by an NF service consumer on behalf of a third NF and the NF service consumer has not indicated supporting of IERSR feature (see 6.2.8), the notification will be sent to the third NF directly, i.e. subsChangeNotifyUri is included in the event subscription, the current status of the events subscribed shall not be included in response. The AMF shall subsequently send a notification to the third NF including the current status of the events subscribed.

If the NF Service Consumer has set the event reporting option as ONE_TIME and if the AMF has included the current status of the events subscribed in the response, then the AMF shall not do any subsequent event notification for the events given in the AmfCreateEventSubscription parameter. If the NF Service Consumer has set the event reporting option as ONE_TIME, the subscribed event as LOCATION_REPORT and the immediateFlag is set to false or absent, the AMF shall send an event notification to notify the current location of the UE after the subscription.

The response, based on operator policy and taking into account the expiry time included in the request, may contain the expiry time, as determined by the AMF, after which the subscription becomes invalid. Once the subscription expires, if the NF Service Consumer wants to keep receiving notifications, it shall create a new subscription in the AMF. The AMF shall not provide the same expiry time for many subscriptions in order to avoid all of them expiring and recreating the subscription at the same time. If the expiry time is not included in the response, the NF Service Consumer shall consider the subscription to be valid without an expiry time.

If the sampling ratio ("sampRatio") attribute is included in the subscription, the AMF shall select a random subset of UEs among target UEs according to the sampling ratio and only report the event(s) related to the selected subset of UEs.

If the NF service consumer is a UDM, the AMF and the UDM both support the "ESSYNC" feature and the subscription is targeting a specific UE with Reference Id(s) included in the subscription, the AMF shall locally store the information that the event subscription is subject to the Event Subscription Synchronization with UDM during EPS to 5GS mobility as specified in clause 5.3.2.4.2. During inter-AMF mobility procedures, the source AMF shall include the "eventSyncInd" IE (in AmfEventSubscriptionAddInfo data type) with the value "true" in the UE Context for the event subscriptions that are subject to Event Subscription Synchronization with UDM.

2b. On failure or redirection, one of the HTTP status code listed in Table 6.2.3.2.3.1-3 shall be returned. For a 4xx/5xx response, the message body shall contain a ProblemDetails structure with the "cause" attribute set to one of the application error listed in Table 6.2.3.2.3.1-3.

5.3.2.2.3 Modification of a subscription

The Subscribe service operation is invoked by a NF Service Consumer, e.g. NEF, towards the AMF, when it needs to modify an existing subscription previously created by itself at the AMF.

The NF Service Consumer shall modify the subscription by using HTTP method PATCH with the URI of the individual subscription resource (see clause 6.2.3.3) to be modified.

See also Figure 5.3.2.2.3-1 below.

Figure 5.3.2.2.3-1 Modification of a Subscription

1. The NF Service Consumer shall send a PATCH request to modify a subscription resource in the AMF. The modification may be for the events subscribed or for updating the event options.

2a. On success, the request is accepted, the AMF shall return the representation of the modified subscription resource or its sub-resource together with the status code 200 OK. When the PATCH request is for modifying the expiry attribute of the options IE of the subscription, then the AMF based on operator policies and taking into account the expiry time included in the request, shall include an expiry time, after which the subscription becomes invalid. Once the subscription expires, if the NF Service Consumer wants to keep receiving notifications, it shall create a new subscription in the AMF, as specified in clause 5.3.2.2.2. The AMF shall not provide the same expiry time for many subscriptions in order to avoid all of them expiring and recreating the subscription at the same time.

2b. On failure or redirection, one of the HTTP status code listed in Table 6.2.3.3.3.1-3 shall be returned. For a 4xx/5xx response, the message body shall contain a ProblemDetails structure with the "cause" attribute set to one of the application error listed in Table 6.2.3.3.3.1-3.

5.3.2.3 Unsubscribe

5.3.2.3.1 General

The Unsubscribe service operation is invoked by a NF Service Consumer, e.g. NEF, towards the AMF, to remove an existing subscription previously created by itself at the AMF.

The NF Service Consumer shall unsubscribe to the subscription by using HTTP method DELETE with the URI of the individual subscription resource (see clause 6.2.3.3) to be deleted.

Figure 5.3.2.3.1-1 Unsubscribe a subscription

1. The NF Service Consumer shall send a DELETE request to delete an existing subscription resource in the AMF.

2a. On success, the request is accepted, the AMF shall reply with the status code 204 indicating the resource identified by subscription ID is successfully deleted in the response message.

2b. On failure or redirection, one of the HTTP status code listed in Table 6.2.3.3.3.2-3 shall be returned. For a 4xx/5xx response, the message body shall contain a ProblemDetails structure with the "cause" attribute set to one of the application error listed in Table 6.2.3.3.3.2-3.

5.3.2.4 Notify

5.3.2.4.1 General

The Notify service operation is invoked by the AMF, to send a notification, towards the notification URI, when certain event included in the subscription has taken place.

The AMF shall use the HTTP method POST, using the notification URI received in the subscription creation as specified in clause 5.3.2.2.2, including e.g. the subscription ID, Event ID(s) for which event has happened, notification correlation ID provided by the NF service consumer at the time of event subscription, to send a notification. See Figure 5.3.2.4.1-1.

Additionally, the Notify service operation shall also be invoked by the AMF, when there is a change of AMF during UE mobility procedures and if the subscription Id changes (i.e. Registration procedures and Handover procedures).

Figure 5.3.2.4.1-1 Notify

1. The AMF shall send a POST request to send a notification.

2a. On success, "204 No content" shall be returned by the NF Service Consumer.

2b. On failure or redirection, the appropriate HTTP status code (e.g. "403 Forbidden") indicating the error shall be returned and appropriate additional error information should be returned.

5.3.2.4.2 Event Subscription Synchronization for specific UE

When the AMF and the UDM both support the "ESSYNC" feature, the AMF may initiate synchronization for event subscriptions with the UDM for the specific UE during EPS to 5GS mobility registration procedure (see clause 4.11.5.2 of 3GPP TS 23.502 [3]), if UE specific event subscriptions from the UDM are available in UE Context.

To initiate event subscription synchronization, when sending notification for subscription change to the UDM, the AMF shall include the event subscription information in the notification request. If subscription change notification is not needed, e.g. when UE registers to the same AMF after moving from EPS, the AMF may send a notification to the subscription change notification URI. The notification request in this case only includes the event subscription information but no event report list,

The AMF shall only include active event subscriptions that are subject to Event Subscription Synchronization with UDM (determined as defined in clause 5.3.2.2.2) in the event subscription information.

For each active subscription, the following information shall include:

– URI of the subscription resource in the AMF; and

– Notification Correlation Id of the subscription; and

– list of Reference Ids, one per event in the subscription; and

– optionally, the URI of old subscription resource on the source AMF, if the subscription Id is changed during the mobility procedure.

When the UDM receives event subscription information from AMF, the UDM shall compare the active event subscriptions in AMF with the active UDM Event Exposure subscriptions using Reference Id(s) and Notification Correlation Id, and perform the following:

– if an event is to be detected by AMF but not existing in the AMF, the UDM shall subscribe the event in AMF by creating a new AMF event subscription or updating an existing AMF event subscription;

– if an event exists in AMF but does not exist in UDM, the UDM shall unsubscribe the event from AMF by removing or update an AMF event subscription.