The Network Exposure Function (NEF) is a functional element that provides application or user related information to the NF service consumers as defined in this specification. The NEF allows the NF consumer(s) to (un)subscribe to notifications of monitoring observed event, and sends the notification to the NF consumer(s) when a subscribed event is detected.

The known NF service consumers are as follows: The Network Data Analytics Function (NWDAF), the Data Collection Coordination Function (DCCF), the Messaging Framework Adaptor Function (MFAF) or the Location Management Function (LMF):

• supports (un)subscribing to notifications of subscribed event(s) from the NEF;
• supports receiving the notifications of subscribed event(s) from the NEF.

The Event Consumer Application Function (Event Consumer AF):

• supports (un)subscribing to notifications of service experience information from the NEF;
• supports receiving the notifications of subscribed event(s) from the NEF.

This service operation is used by an NF service consumer to subscribe to notifications on specified event(s) or modify an existing subscription. The following are the types of events for which a subscription to notifications can be created by the NWDAF, the DCCF, or the MFAF as the NF service consumer:

• Service experience;
• UE mobility;
• UE communication;
• Exceptions;
• User Data Congestion;
• Dispersion;
• Performance Data information; and
• Collective Behaviour information.

The following are the types of events for which a subscription can be made by the NWDAF, DCCF, MFAF, or Event Consumer AF as the NF service consumer:

• Media Streaming QoE metrics;

The following are the types of events for which a subscription to notifications can be created by the LMF as the NF service consumer:

• GNSS Assistance Data information.

The following are the types of events for which a subscription can be made by the Event Consumer AF as the NF service consumer:

• Media Streaming Consumption reports;
• Media Streaming Network Assistance invocation;
• Media Streaming Dynamic Policy invocation; and
• Media Streaming access activity.

The following procedures using the Nnef_EventExposure_Subscribe service operation are supported:

• creating a new subscription;
• modifying an existing subscription.

Figure 4.2.2.2.2-1 illustrates the creation of a Network Exposure Event Subscription.

To subscribe to event notifications, the NF service consumer shall send an HTTP POST request to the NEF with: "{apiRoot}/­nnef-eventexposure/­<apiVersion>/­subscriptions" as request URI as shown in step 1 of Figure 4.2.2.2.2-1, and the "NefEventExposureSubsc" data structure as request body. The "NefEventExposureSubsc" data structure shall include:

• a URI where to receive the requested notifications as "notifUri" attribute;
• a Notification Correlation Identifier assigned by the NF service consumer for the requested notifications as "notifId" attribute; and
• description of subscribed event information as "eventsSubs" attribute by using one or more "NefEventSubs" data.

The "NefEventExposureSubsc" data structure may also include:

• the description of the event reporting information as "eventsRepInfo" attribute.
• a specific Authorization AS provisioned Data Access Profile Identifier as "dataAccProfId" attribute, if the feature "DataAccProfileId" is supported and the subscribed events including "MS_QOE_METRICS", "MS_CONSUMPTION", "MS_NET_ASSIST_INVOCATION", "MS_DYN_POLICY_INVOCATION", and/or "MS_ACCESS_ACTIVITY".

The "NefEventSubs" data structure shall include:

• an event to subscribe to as a "event" attribute; and
• event filter information as "eventFilter" attribute associated with the event;

and may include:

• event-specific reporting information, within the "eventRepInfo" attribute, if the "PerEventRepReq" feature is supported.

The "eventsRepInfo" attribute may include:

• event notification method (periodic, one time, on event detection) as "notifMethod" attribute;
• Maximum Number of Reports as "maxReportNbr" attribute;
• Monitoring Duration as "monDur" attribute;
• repetition period for periodic reporting as "repPeriod" attribute;
• immediate reporting indication as "immRep" attribute;
• sampling ratio as "sampRatio" attribute;
• partitioning criteria for partitioning the UEs before performing sampling as "partitionCriteria" attribute if the EneNA feature is supported;
• group reporting guard time as "grpRepTime" attribute;
• a notification flag as "notifFlag" attribute if the EneNA feature is supported; and/or
• notification muting exception instructions within the "notifFlagInstruct" attribute, if the EnhDataMgmt feature is supported and the "notifFlag" attribute is provided and set to "DEACTIVATE".

When the "PerEventRepReq" feature is supported and the "eventsRepInfo" attribute is present, the common events reporting requirements provided within the "eventsRepInfo" attribute shall apply to a subscribed event only when no event-specific reporting requirements are provided within the "eventsSubs" attribute via the "eventRepInfo" attribute of the NefEventSubs data structure for this subscribed event, as specified above. If the NEF cannot successfully fulfil the received HTTP POST request due to an internal error or an error in the HTTP POST request, the NEF shall send an HTTP error response as specified in clause 5.1.7. Upon successful reception of an HTTP POST request with "{apiRoot}/­nnef-eventexposure/­<apiVersion>/­subscriptions" as request URI and "NefEventExposureSubsc" data structure as request body, the NEF shall create a new "Individual Network Exposure Event Subscription" resource, store the subscription and send an HTTP "201 Created" response, as shown in step 2 of Figure 4.2.2.2.2-1. The NEF shall include in the "201 Created" response:

• a Location header field; and
• an "NefEventExposureSubsc" data type in the content.

The Location header field shall contain the URI of the created individual application session context resource i.e. "{apiRoot}/­nnef-eventexposure/­<apiVersion>/­subscriptions/­{subscriptionId}". The "NefEventExposureSubsc" data type content shall contain the representation of the created "Individual Network Exposure Event Subscription". When the "monDur" attribute is included in the response by the NEF, it represents NEF selected expiry time that is equal or less than the expiry time received in the request. When the "immRep" attribute is included and set to "true" in the subscription and the subscribed events are available, the NEF shall include the reports of the events subscribed, if available, in the HTTP POST response. When the sampling ratio attribute, as "sampRatio", is included in the subscription without a "partitionCriteria" attribute, the NEF shall select a random subset of UEs among the target UEs according to the sampling ratio and only report the event(s) related to the selected subset of UEs. If the "partitionCriteria" attribute is additionally included, then the NEF shall first partition the UEs according to the value of the "partitionCriteria" attribute and then select a random subset of UEs from each partition according to the sampling ratio and only report the event(s) related to the selected subsets of UEs. When the group reporting guard time, as "grpRepTime" attribute, is included in the subscription, the NEF shall accumulate all the event reports for the target UEs until the group reporting guard time expires. Then, the NEF shall notify the NF service consumer using the Nnef_EventExposure_Notify service operation, as described in clause 4.2.2.4. When the "notifFlag" attribute is included and set to "DEACTIVATE" in the request, the NEF shall mute the event notification and store the available events until the NF service consumer requests to retrieve them by setting the "notifFlag" attribute to "RETRIEVAL" or until a muting exception occurs (e.g. full buffer). When a muting exception occurs, the NEF may consider the contents of the "notifFlagInstruct" attribute (if provided) and/or local configuration to determine its actions. If the EnhDataMgmt feature is supported and the NEF accepts the muting instructions provided in the "notifFlag" and/or the "notifFlagInstruct" attributes, it may indicate the applied muting notification settings within the "mutingSetting" attribute in the response. If the NEF does not accept the muting instructions provided in the "notifFlag" and/or the "notifFlagInstruct" attributes, it shall send an HTTP "403 Forbidden" error response including the "cause" attribute set to "MUTING_INSTR_NOT_ACCEPTED".

Figure 4.2.2.2.3-1 illustrates the modification of an existing subscription.

To modify an existing subscription to event notifications, the NF service consumer shall send an HTTP PUT request with: "{apiRoot}/­nnef-eventexposure/­<apiVersion>/­subscriptions/­{subscriptionId}" as request URI, as shown in step 1 of Figure 4.2.2.2.3-1, where "{subscriptionId}" is the subscription correlation ID of the existing subscription. The "NefEventExposureSubsc" data structure is included as request body as described in clause 4.2.2.2.2. If the NEF cannot successfully fulfil the received HTTP PUT request due to an internal error or an error in the HTTP PUT request, the NEF shall send an HTTP error response as specified in clause 5.1.7. If the feature "ES3XX" is supported, and the NEF determines the received HTTP PUT request needs to be redirected, the NEF shall send an HTTP redirect response as specified in clause 6.10.9 of TS 29.500. Upon successful reception of an HTTP PUT request with: "{apiRoot}/­nnef-eventexposure/­<apiVersion>/­subscriptions/­{subscriptionId}" as request URI and "NefEventExposureSubsc" data structure as request body, the NEF shall update the subscription and send an HTTP "200 OK" response with the "NefEventExposureSubsc" data structure as response body containing the representation of the modified "Individual Network Exposure Event Subscription", or an HTTP "204 No Content" response, as shown in step 2 of Figure 4.2.2.2.3-1. When the "monDur" attribute is included in the response by the NEF, it represents NEF selected expiry time that is equal or less than the expiry time received in the request. When the "immRep" attribute is included and sets to "true" in the subscription and the subscribed events are available, the NEF shall include the reports of the events subscribed, if available, in the HTTP PUT response. When the sampling ratio, as "sampRatio" attribute, is included in the subscription without a "partitionCriteria" attribute, the NEF shall select a random subset of UEs among the target UEs according to the sampling ratio and only report the event(s) related to the selected subset of UEs. If the "partitionCriteria" attribute is additionally included, then the NEF shall first partition the UEs according to the value of the "partitionCriteria" attribute and then select a random subset of UEs from each partition according to the sampling ratio and only report the event(s) related to the selected subsets of UEs. When the group reporting guard time, as "grpRepTime" attribute, is included in the subscription, the NEF shall accumulate all the event reports for the target UEs until the group reporting guard time expires. Then, the NEF shall notify the NF service consumer using the Nnef_EventExposure_Notify service operation, as described in clause 4.2.2.4. When the "notifFlag" attribute is included, and set to "DEACTIVATE" in the request, the NEF shall mute the event notification and store the available events until the NF service consumer requests to retrieve them by setting the "notifFlag" attribute to "RETRIEVAL" or until a muting exception occurs (e.g. full buffer). When a muting exception occurs, the NEF may consider the contents of the "notifFlagInstruct" attribute (if provided) and/or local configuration to determine its actions; if the "notifFlag" attribute is set to "RETRIEVAL" in the request, the NEF shall send the stored events to the NF service consumer, and mute the event notification again and store available events; if the "notifFlag" attribute is set to "ACTIVATE" and the event notifications are muted (due to a previously received "DECATIVATE" value), the NEF shall unmute the event notification, i.e. start sending again notifications for available events. If the EnhDataMgmt feature is supported and the NEF accepts the muting instructions provided in the "notifFlag" and/or the "notifFlagInstruct" attributes, it may indicate the applied muting notification settings within the "mutingSetting" attribute in the response. If the NEF does not accept the muting instructions provided in the "notifFlag" and/or the "notifFlagInstruct" attributes, it shall send an HTTP "403 Forbidden" error response including the "cause" attribute set to "MUTING_INSTR_NOT_ACCEPTED".

This service operation is used by an NF service consumer to unsubscribe from event notifications. The following procedure using the Nnef_EventExposure_Unsubscribe service operation is supported:

• unsubscription from event notifications.

Figure 4.2.2.3.2-1 illustrates the unsubscription from event notifications.

To unsubscribe from event notifications, the NF service consumer shall send an HTTP DELETE request with "{apiRoot}/­nnef-eventexposure/­<apiVersion>/­subscriptions/­{subscriptionId}" as request URI, as shown in step 1 of Figure 4.2.2.3.2-1, where "{subscriptionId}" is the subscription correlation identifier of the existing subscription resource that is to be deleted. If the NEF cannot successfully fulfil the received HTTP DELETE request due to an internal error or an error in the HTTP DELETE request, the NEF shall send an HTTP error response as specified in clause 5.1.7. If the feature "ES3XX" is supported, and the NEF determines the received HTTP DELETE request needs to be redirected, the NEF shall send an HTTP redirect response as specified in clause 6.10.9 of TS 29.500. Upon successful reception of an HTTP DELETE request with: "{apiRoot}/­nnef-eventexposure/­<apiVersion>/­subscriptions/­{subscriptionId}" as request URI, the NEF shall remove the corresponding subscription and send an HTTP "204 No Content" response, as shown in step 2 of Figure 4.2.2.3.2-1.

The Nnef_EventExposure_Notify service operation enables the NEF to notify the NF service consumer(s) that the previously subscribed application related event occurred. The following procedure using the Nnef_EventExposure_Notify service operation is supported:

• notification about subscribed events.

Figure 4.2.2.4.2-1 illustrates the notification about subscribed events.

If the NEF observes application related event(s) for which an NF service consumer has subscribed, the NEF shall send an HTTP POST request as shown in step 1 of Figure 4.2.2.4.2-1, with the "{notifUri}" as request URI containing the value previously provided by the NF service consumer within the corresponding subscription, and the "NefEventExposureNotif" data structure. The "NefEventExposureNotif" data structure shall include:

• notification correlation ID provided by the NF service consumer during the subscription as "notifId" attribute; and
• information about the observed event(s) within the "eventNotifs" attribute that shall contain for each observed event an "NefEventNotification" data structure that shall include:
  • the application related event as "event" attribute;
  • the time at which the event was observed encoded as "timeStamp" attribute;
  • if the "event" attribute is "SVC_EXPERIENCE", service experience information about the application involved in the reported event in the "svcExprcInfos" attribute;
  • if the "event" attribute is "UE_MOBILITY", UE mobility information assoicated with the application as "ueMobilityInfos" attribute;
  • if the "event" attribute is "UE_COMM", UE communication information assoicated with the application as "ueCommInfos" attribute;
  • if the "event" attribute is "EXCEPTIONS", exceptions information associated with a service flow as "excepInfos" attribute;
  • if the "event" attribute is "PERF_DATA", Performance Data Analytics related information as "perfDataInfos" attribute;
  • if the "event" attribute is "COLLECTIVE_BEHAVIOUR", collective behaviour information associated with the UEs and its applications as "collBhvrInfs" attribute;
  • if the "event" attribute is "USER_DATA_CONGESTION", user data congestion information collected for an AF application as "congestionInfos" attribute;
  • if the "event" attribute is "DISPERSION", UE dispersion information collected for an AF as "dispersionInfos" attribute;
  • if the "event" attribute is "MS_QOE_METRICS",
    • Media Streaming QoE metrics information collected for an UE application via the Data Collection AF as "msQoeMetrInfos" attribute; This attribute is deprecated; the attribute "msQoeMetrics" should be used instead;
    • if the "MSEventExposure" feature is supported, the Media Streaming QoE metrics information collected for an UE application via the Data Collection AF as "msQoeMetrics" attribute;
  • if the "event" attribute is "MS_CONSUMPTION",
    • Media Streaming Consumption reports information collected for an UE application via the Data Collection AF as "msConsumpInfos" attribute; This attribute is deprecated; the attribute "msConsumpReports" should be used instead;
    • if the "MSEventExposure" feature is supported, the Media Streaming Consumption reports collected for an UE application via the Data Collection AF as "msConsumpReports" attribute;
  • if the "event" attribute is "MS_NET_ASSIST_INVOCATION",
    • Media Streaming Network Assistance invocation information collected for an UE application via the Data Collection AF as "msNetAssInvInfos" attribute; This attribute is deprecated; the attribute "msNetAssistInvocation" should be used instead;
    • if the "MSEventExposure" feature is supported, the Media Streaming Network Assistance invocation collected for an UE application via the Data Collection AF as "msNetAssistInvocation" attribute;
  • if the "event" attribute is "MS_DYN_POLICY_INVOCATION",
    • Media Streaming Dynamic Policy invocations information collected for an UE application via the Data Collection AF as "msDynPlyInvInfos" attribute; This attribute is deprecated; the attribute "msDynPlyInvocation" should be used instead;
    • if the "MSEventExposure" feature is supported, the Media Streaming Dynamic Policy invocation collected for an UE application via the Data Collection AF as "msDynPlyInvocation" attribute;
  • if the "event" attribute is "MS_ACCESS_ACTIVITY",
    • Media Streaming access activity information collected for an UE application via the Data Collection AF as "msAccActInfos" attribute; This attribute is deprecated; the attribute "msAccess" should be used instead.
    • if the "MSEventExposure" feature is supported, the Media Streaming access activity collected for an UE application via the Data Collection AF as "msAccess" attribute; and
  • if the "event" attribute is "GNSS_ASSISTANCE_DATA", GNSS Assistance Data information within the "gnssAssistDataInfo" attribute;
  • if the "event" attribute is "DATA_VOLUME_TRANSFER_TIME", data volume transfer time information assoicated with the application as "datVolTransTimeInfos" attribute.

If the NF service consumer cannot successfully fulfil the received HTTP POST request due to an internal error or an error in the HTTP POST request, the NF service consumer shall send an HTTP error response as specified in clause 5.1.7. If the feature "ES3XX" is supported, and the NF service consumer determines the received HTTP POST request needs to be redirected, the NF service consumer shall send an HTTP redirect response as specified in clause 6.10.9 of TS 29.500. Upon successful reception of an HTTP POST request with "{notifUri}" as request URI and "NefEventExposureNotif" data structure as request body, the NF service consumer shall send an HTTP "204 No Content" response, as shown in step 2 of Figure 4.2.2.4.2-1, in case of a successful processing.