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NEF services and slicing impacts

The Network Exposure Function (NEF) in 5G inherits from the SCEF (Service Capability Exposure Function) in 4G and encompasses many functionnalities among which :

  • exposure at NFs, in particular AFs, of capabilities or events occurring at other NFs;
  • exposure at NFs, in particular AFs, of capabilities or events occurring at other NFs;
  • provisioning of information coming from AFs to NFs in the 5GC e.g. Expected UE Behaviour, 5GLAN group information and service specific information;
  • support for analytics exposure i.e. NWDAF analytics possibly exposed by NEF for external parties AFs.

These functionalities are expressed in terms of NEF services.

NEF services and slicing impacts :

  • The majority of NEF services are not impacted by slicing aspects introduced in 5G typically because they relate to the UE itself independently of the slice (S-NSSAI) the UE is using e.g. Nnef_Location.
  • Some NEF services indirectly relate to slicing information because they relate to PDU session(s) and a PDU session is activated for a (S-NSSAI, DNN) combination. This is the case for NEF services related to Non-IP Data Delivery (NIDD), i.e. NIDD Nnef_SMContext, Nnef_NIDD and Nnef_NIDDConfiguration.
  • Some NEF services also indirectly relate to slicing information because they relate to application(s) and an application can be identified by a (S-NSSAI, DNN) combination in 5G (although other means are also possible) This is the case for Nnef_ServiceParameter, Nnef_TrafficInfluence and Nnef_ServiceParameter;
  • NEF_Parameter_Provision allows an AF to configure parameters in the UDM for a (S-NSSAI, DNN) combination for managing 5G VN groups;
  • Some NEF services relate to slicing e.g. Nnef_AnalyticsExposure because it’s possible for an AF to obtain network analytics information related to a specific slice type, i.e. a filter is possible in the subscription request sent to the NEF. For event exposure and analytics exposure, when the filter on S-NSSAI is not possible, the deployment of a NEF dedicated to a slice allows the AF to obtain notifications of the events in the slice, which is applicablewhen a slice is dedicated to an NPN (Non-Public Network), i.e. PNI-NPN.

NEF deployment and slicing impacts :

  • 3GPP specifications make no assumption on NEF deployment in the PLMN and the operator can deploy the NEF per type of NEF service and/or per slice type.
  • NEF centralization allows saving OPEX/CAPEX with a limited number of NEF(s) in the PLMN and also saving signalling for subscriptions at the NEF and from the NEF towards the other NFs in the PLMN.
  • NEF distribution avoids tromboning effects in the control plane for services such as edge computing or URLLC services where AFs are supposed to be distributed: NEF may be deployed close to AFs.
  • NEF distribution is also a solution to provide event exposure and network analytics exposure to an AF on a dedicated slice when the subscription to such events per slice type is not possible in the standard.
  • Implementing one or a few centralized NEF(s) and more distributed NEFs in the PLMN is the most realistic situation to manage the above cases.

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