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full Contents for  TS 23.501  Word version:   16.4.0

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6  Network Functions
6.1  General
Clause 6 provides the functional description of the Network Functions and network entities in the 5GC, and the principles for Network Function and Network Function Service discovery and selection.
6.2  Network Function Functional description
6.2.1  AMF
The Access and Mobility Management function (AMF) includes the following functionality. Some or all of the AMF functionalities may be supported in a single instance of an AMF:
  • Termination of RAN CP interface (N2).
  • Termination of NAS (N1), NAS ciphering and integrity protection.
  • Registration management.
  • Connection management.
  • Reachability management.
  • Mobility Management.
  • Lawful intercept (for AMF events and interface to LI System).
  • Provide transport for SM messages between UE and SMF.
  • Transparent proxy for routing SM messages.
  • Access Authentication.
  • Access Authorization.
  • Provide transport for SMS messages between UE and SMSF.
  • Security Anchor Functionality (SEAF) as specified in TS 33.501.
  • Location Services management for regulatory services.
  • Provide transport for Location Services messages between UE and LMF as well as between RAN and LMF.
  • EPS Bearer ID allocation for interworking with EPS.
  • UE mobility event notification.
  • Support for Control Plane CIoT 5GS Optimisation.
  • Support for User Plane CIoT 5GS Optimisation.
  • Provisioning of external parameters (Expected UE Behaviour parameters or Network Configuration parameters).
  • Support for Network Slice-Specific Authentication and Authorization.
NOTE 1:
Regardless of the number of Network functions, there is only one NAS interface instance per access network between the UE and the CN, terminated at one of the Network functions that implements at least NAS security and Mobility Management.
In addition to the functionalities of the AMF described above, the AMF may include the following functionality to support non-3GPP access networks:
  • Support of N2 interface with N3IWF/TNGF. Over this interface, some information (e.g. 3GPP Cell Identification) and procedures (e.g. Handover related) defined over 3GPP access may not apply, and non-3GPP access specific information may be applied that do not apply to 3GPP accesses.
  • Support of NAS signalling with a UE over N3IWF/TNGF. Some procedures supported by NAS signalling over 3GPP access may be not applicable to untrusted non-3GPP (e.g. Paging) access.
  • Support of authentication of UEs connected over N3IWF/TNGF.
  • Management of mobility, authentication, and separate security context state(s) of a UE connected via a non-3GPP access or connected via a 3GPP access and a non-3GPP access simultaneously.
  • Support as described in clause 5.3.2.3 a co-ordinated RM management context valid over a 3GPP access and a Non 3GPP access.
  • Support as described in clause 5.3.3.4 dedicated CM management contexts for the UE for connectivity over non-3GPP access.
NOTE 2:
Not all of the functionalities are required to be supported in an instance of a Network Slice.
In addition to the functionalities of the AMF described above, the AMF may include policy related functionalities as described in clause 6.2.8 in TS 23.503.
The AMF uses the N14 interface for AMF re-allocation and AMF to AMF information transfer. This interface may be be either intra-PLMN or inter-PLMN (e.g. in the case of inter-PLMN mobility).
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6.2.2  SMFWord-p. 331
The Session Management function (SMF) includes the following functionality. Some or all of the SMF functionalities may be supported in a single instance of a SMF:
  • Session Management e.g. Session Establishment, modify and release, including tunnel maintain between UPF and AN node.
  • UE IP address allocation & management (including optional Authorization). The UE IP address may be received from a UPF or from an external data network.
  • DHCPv4 (server and client) and DHCPv6 (server and client) functions.
  • Functionality to respond to Address Resolution Protocol (ARP) requests and / or IPv6 Neighbour Solicitation requests based on local cache information for the Ethernet PDUs. The SMF responds to the ARP and / or the IPv6 Neighbour Solicitation Request by providing the MAC address corresponding to the IP address sent in the request.
  • Selection and control of UP function, including controlling the UPF to proxy ARP or IPv6 Neighbour Discovery, or to forward all ARP/IPv6 Neighbour Solicitation traffic to the SMF, for Ethernet PDU Sessions.
  • Configures traffic steering at UPF to route traffic to proper destination.
  • 5G VN group management, e.g. maintain the topology of the involved PSA UPFs, establish and release the N19 tunnels between PSA UPFs, configure traffic forwarding at UPF to apply local switching, N6-based forwarding or N19-based forwarding.
  • Termination of interfaces towards Policy control functions.
  • Lawful intercept (for SM events and interface to LI System).
  • Charging data collection and support of charging interfaces.
  • Control and coordination of charging data collection at UPF.
  • Termination of SM parts of NAS messages.
  • Downlink Data Notification.
  • Initiator of AN specific SM information, sent via AMF over N2 to AN.
  • Determine SSC mode of a session.
  • Support for Control Plane CIoT 5GS Optimisation.
  • Support of header compression.
  • Act as I-SMF in deployments where I-SMF can be inserted, removed and relocated.
  • Provisioning of external parameters (Expected UE Behaviour parameters or Network Configuration parameters).
  • Support P-CSCF discovery for IMS services.
  • Roaming functionality:
    • Handle local enforcement to apply QoS SLAs (VPLMN).
    • Charging data collection and charging interface (VPLMN).
    • Lawful intercept (in VPLMN for SM events and interface to LI System).
    • Support for interaction with external DN for transport of signalling for PDU Session authentication/authorization by external DN.
    • Instructs UPF and NG-RAN to perform redundant transmission on N3/N9 interfaces.
NOTE:
Not all of the functionalities are required to be supported in an instance of a Network Slice.
In addition to the functionalities of the SMF described above, the SMF may include policy related functionalities as described in clause 6.2.2 in TS 23.503.
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6.2.3  UPFWord-p. 332
The User plane function (UPF) includes the following functionality. Some or all of the UPF functionalities may be supported in a single instance of a UPF:
  • Anchor point for Intra-/Inter-RAT mobility (when applicable).
  • Allocation of UE IP address/prefix (if supported) in response to SMF request.
  • External PDU Session point of interconnect to Data Network.
  • Packet routing & forwarding (e.g. support of Uplink classifier to route traffic flows to an instance of a data network, support of Branching point to support multi-homed PDU Session, support of traffic forwarding within a 5G VN group (UPF local switching, via N6, via N19)).
  • Packet inspection (e.g. Application detection based on service data flow template and the optional PFDs received from the SMF in addition).
  • User Plane part of policy rule enforcement, e.g. Gating, Redirection, Traffic steering).
  • Lawful intercept (UP collection).
  • Traffic usage reporting.
  • QoS handling for user plane, e.g. UL/DL rate enforcement, Reflective QoS marking in DL.
  • Uplink Traffic verification (SDF to QoS Flow mapping).
  • Transport level packet marking in the uplink and downlink.
  • Downlink packet buffering and downlink data notification triggering.
  • Sending and forwarding of one or more "end marker" to the source NG-RAN node.
  • Functionality to respond to Address Resolution Protocol (ARP) requests and / or IPv6 Neighbour Solicitation requests based on local cache information for the Ethernet PDUs. The UPF responds to the ARP and / or the IPv6 Neighbour Solicitation Request by providing the MAC address corresponding to the IP address sent in the request.
  • Packet duplication in downlink direction and elimination in uplink direction in GTP-U layer.
  • TSN Translator (NW-TT) functionality.
  • High latency communication, see clause 5.31.8.
  • ATSSS Steering functionality to steer the MA PDU Session traffic, refer to clause 5.32.6.
  • NOTE:
    Not all of the UPF functionalities are required to be supported in an instance of user plane function of a Network Slice.
  • Inter PLMN UP Security (IPUPS) functionality, specified in clause 5.8.2.14.
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6.2.4  PCF
The Policy Control Function (PCF) includes the following functionality:
  • Supports unified policy framework to govern network behaviour.
  • Provides policy rules to Control Plane function(s) to enforce them.
  • Accesses subscription information relevant for policy decisions in a Unified Data Repository (UDR).
NOTE:
The PCF accesses the UDR located in the same PLMN as the PCF.
The details of the PCF functionality are defined in clause 6.2.1 of TS 23.503.
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6.2.5  NEFWord-p. 333
The Network Exposure Function (NEF) supports the following independent functionality:
  • Exposure of capabilities and events:
  • NF capabilities and events may be securely exposed by NEF for e.g. 3rd party, Application Functions, Edge Computing as described in clause 5.13.
    NEF stores/retrieves information as structured data using a standardized interface (Nudr) to the Unified Data Repository (UDR).
  • Secure provision of information from external application to 3GPP network:
  • It provides a means for the Application Functions to securely provide information to 3GPP network, e.g. Expected UE Behaviour, 5GLAN group information and service specific information. In that case the NEF may authenticate and authorize and assist in throttling the Application Functions.
  • Translation of internal-external information:
  • It translates between information exchanged with the AF and information exchanged with the internal network function. For example, it translates between an AF-Service-Identifier and internal 5G Core information such as DNN, S-NSSAI, as described in clause 5.6.7.
    In particular, NEF handles masking of network and user sensitive information to external AF's according to the network policy.
  • The Network Exposure Function receives information from other network functions (based on exposed capabilities of other network functions). NEF stores the received information as structured data using a standardized interface to a Unified Data Repository (UDR). The stored information can be accessed and "re-exposed" by the NEF to other network functions and Application Functions, and used for other purposes such as analytics.
  • A NEF may also support a PFD Function: The PFD Function in the NEF may store and retrieve PFD(s) in the UDR and shall provide PFD(s) to the SMF on the request of SMF (pull mode) or on the request of PFD management from NEF (push mode), as described in TS 23.503.
  • A NEF may also support a 5GLAN Group Management Function: The 5GLAN Group Management Function in the NEF may store the 5GLAN group information in the UDR via UDM as described in TS 23.502.
  • Exposure of analytics:
  • NWDAF analytics may be securely exposed by NEF for external party, as specified in TS 23.288.
  • Retrieval of data from external party by NWDAF:
  • Data provided by the external party may be collected by NWDAF via NEF for analytics generation purpose. NEF handles and forwards requests and notifications between NWDAF and AF, as specified in TS 23.288.
  • Support of Non-IP Data Delivery:
  • NEF provides a means for management of NIDD configuration and delivery of MO/MT unstructured data by exposing the NIDD APIs as described in TS 23.502 on the N33/Nnef reference point. See clause 5.31.5.
A specific NEF instance may support one or more of the functionalities described above and consequently an individual NEF may support a subset of the APIs specified for capability exposure.
NOTE:
The NEF can access the UDR located in the same PLMN as the NEF.
The services provided by the NEF are specified in clause 7.2.8.
The IP address(es)/port(s) of the NEF may be locally configured in the AF, or the AF may discover the FQDN or IP address(es)/port(s) of the NEF by performing a DNS query using the External Identifier of an individual UE or using the External Group Identifier of a group of UEs, or, if the AF is trusted by the operator, the AF may utilize the NRF to discover the FQDN or IP address(es)/port(s) of the NEF as described in clause 6.3.14.
For external exposure of services related to specific UE(s), the NEF resides in the HPLMN. Depending on operator agreements, the NEF in the HPLMN may have interface(s) with NF(s) in the VPLMN.
When a UE is capable of switching between EPC and 5GC, an SCEF+NEF is used for service exposure. See clause 5.17.5 for a description of the SCEF+NEF.
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6.2.5.1  Support for CAPIFWord-p. 334
When an NEF is used for external exposure, the CAPIF may be supported. When CAPIF is supported, an NEF that is used for external exposure supports the CAPIF API provider domain functions. The CAPIF and associated API provider domain functions are specified in TS 23.222.
6.2.5a  Intermediate NEF [R16]
The Intermediate NEF (I-NEF) is used for interworking between NFs in the VPLMN and the NEF. The I-NEF is optional and is only used in roaming scenarios. NFs in the VPLMN are configured with the I-NEF identity.
NOTE:
Deployments can choose to co-locate I-NEF with another NF.
The functionality provided by the I-NEF may include the following:
  • Normalization of reports according to roaming agreements between VPLMN and HPLMN (e.g. the I-NEF may change the location granularity in a report from cell level to a level that is appropriate for the HPLMN); and
  • Generation of charging/accounting information for Monitoring Event Reports that are sent to the HPLMN.
If the UE is capable of mobility between EPS and 5GS, the network is expected to associate the UE with an SCEF+NEF node for Service Capability Exposure. If the I-NEF is deployed in an interworking scenario, it is assumed that the I-NEF also implements IWK-SCEF functionality (as described in TS 23.682) and the I-NEF shall connect with an SCEF+NEF node.
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6.2.6  NRF
The Network Repository Function (NRF) supports the following functionality:
  • Supports service discovery function. Receive NF Discovery Request from NF instance or SCP, and provides the information of the discovered NF instances (be discovered) to the NF instance or SCP.
  • Supports P-CSCF discovery (specialized case of AF discovery by SMF).
  • Maintains the NF profile of available NF instances and their supported services.
  • Notifies about newly registered/updated/ deregistered NF instances along with its NF services to the subscribed NF service consumer or SCP.
NF profile of NF instance maintained in an NRF includes the following information:
  • NF instance ID.
  • NF type.
  • PLMN ID.
  • Network Slice related Identifier(s) e.g. S-NSSAI, NSI ID.
  • FQDN or IP address of NF.
  • NF capacity information.
  • NF priority information.
  • NOTE 1:
    This parameter is used for AMF selection, if applicable, as specified in clause 6.3.5. See clause 6.1.6.2.2 of TS 29.510 for its detailed use.
  • NF Set ID.
  • NF Service Set ID of the NF service instance.
  • NF Specific Service authorization information.
  • if applicable, Names of supported services.
  • Endpoint Address(es) of instance(s) of each supported service.
  • Identification of stored data/information.
  • NOTE 2:
    This is only applicable for a UDR profile. See applicable input parameters for Nnrf_NFManagement_NFRegister service operation in TS 23.502, clause 5.2.7.2.2. This information applicability to other NF profiles is implementation specific.
  • Other service parameter, e.g., DNN or DNN list, notification endpoint for each type of notification that the NF service is interested in receiving.
  • Location information for the NF instance.
  • NOTE 3:
    This information is operator specific. Examples of such information can be geographical location, data center.
  • TAI(s).
  • NF load information.
  • Routing Indicator, for UDM and AUSF.
  • One or more GUAMI(s), in the case of AMF.
  • SMF area identity(ies) in the case of UPF.
  • UDM Group ID, range(s) of SUPIs, range(s) of GPSIs, range(s) of internal group identifiers, range(s) of external group identifiers for UDM.
  • UDR Group ID, range(s) of SUPIs, range(s) of GPSIs, range(s) of external group identifiers for UDR.
  • AUSF Group ID, range(s) of SUPIs for AUSF.
  • PCF Group ID, range(s) of SUPIs for PCF.
  • HSS Group ID, set(s) of IMPIs, set(s) of IMPU, for HSS.
  • Supported Analytics ID(s), NWDAF Serving Area information (i.e. list of TAIs for which the NWDAF can provide analytics) if available in the case of NWDAF.
  • NOTE 4:
    The NWDAF's Serving Area information is common to all its supported Analytics IDs.
  • Event ID(s) supported by AFs, in the case of NEF.
  • Application ID(s) supported by AFs, in the case of NEF.
  • NOTE 5:
    This is applicable when NEF exposes AF information for analytics purpose as detailed in TS 23.288.
    NOTE 6:
    It is expected service authorization information is usually provided by OA&M system, and it can also be included in the NF profile in the case that e.g. an NF instance has an exceptional service authorization information.
    NOTE 7:
    The NRF may store a mapping between UDM Group ID and SUPI(s), UDR Group ID and SUPI(s), AUSF Group ID and SUPI(s) and PCF Group ID and SUPI(s), to enable discovery of UDM, UDR, AUSF and PCF using SUPI, SUPI ranges as specified in clause 6.3 or interact with UDR to resolve the UDM Group ID/UDR Group ID/AUSF Group ID/PCF Group ID based on UE identity, e.g. SUPI (see clause 6.3.1 for details).
  • IP domain list as described in clause 6.1.6.2.21 of TS 29.510, Range(s) of (UE) IPv4 addresses or Range(s) of (UE) IPv6 prefixes, in the case of BSF.
In the context of Network Slicing, based on network implementation, multiple NRFs can be deployed at different levels (see clause 5.15.5):
  • PLMN level (the NRF is configured with information for the whole PLMN),
  • shared-slice level (the NRF is configured with information belonging to a set of Network Slices),
  • slice-specific level (the NRF is configured with information belonging to an S-NSSAI).
In the context of roaming, multiple NRFs may be deployed in the different networks (see clause 4.2.4):
  • the NRF(s) in the Visited PLMN (known as the vNRF) configured with information for the visited PLMN.
  • the NRF(s) in the Home PLMN (known as the hNRF) configured with information for the home PLMN, referenced by the vNRF via the N27 interface.
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6.2.7  UDMWord-p. 336
The Unified Data Management (UDM) includes support for the following functionality:
  • Generation of 3GPP AKA Authentication Credentials.
  • User Identification Handling (e.g. storage and management of SUPI for each subscriber in the 5G system).
  • Support of de-concealment of privacy-protected subscription identifier (SUCI).
  • Access authorization based on subscription data (e.g. roaming restrictions).
  • UE's Serving NF Registration Management (e.g. storing serving AMF for UE, storing serving SMF for UE's PDU Session).
  • Support to service/session continuity e.g. by keeping SMF/DNN assignment of ongoing sessions.
  • MT-SMS delivery support.
  • Lawful Intercept Functionality (especially in outbound roaming case where UDM is the only point of contact for LI).
  • Subscription management.
  • SMS management.
  • 5GLAN group management handling.
  • Support of external parameter provisioning (Expected UE Behaviour parameters or Network Configuration parameters).
To provide this functionality, the UDM uses subscription data (including authentication data) that may be stored in UDR, in which case a UDM implements the application logic and does not require an internal user data storage and then several different UDMs may serve the same user in different transactions.
NOTE 1:
The interaction between UDM and HSS, when they are deployed as separate network functions, is defined in TS 23.632 and TS 29.563 or it is implementation specific.
NOTE 2:
The UDM is located in the HPLMN of the subscribers it serves, and access the information of the UDR located in the same PLMN.
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6.2.8  AUSFWord-p. 337
The Authentication Server Function (AUSF) supports the following functionality:
  • Supports authentication for 3GPP access and untrusted non-3GPP access as specified in TS 33.501.
  • Support for Network Slice-Specific Authentication and Authorization as specified in TS 23.502.
6.2.9  N3IWF
The functionality of N3IWF in the case of untrusted non-3GPP access includes the following:
  • Support of IPsec tunnel establishment with the UE: The N3IWF terminates the IKEv2/IPsec protocols with the UE over NWu and relays over N2 the information needed to authenticate the UE and authorize its access to the 5G Core Network.
  • Termination of N2 and N3 interfaces to 5G Core Network for control - plane and user-plane respectively.
  • Relaying uplink and downlink control-plane NAS (N1) signalling between the UE and AMF.
  • Handling of N2 signalling from SMF (relayed by AMF) related to PDU Sessions and QoS.
  • Establishment of IPsec Security Association (IPsec SA) to support PDU Session traffic.
  • Relaying uplink and downlink user-plane packets between the UE and UPF. This involves:
  • De-capsulation/ encapsulation of packets for IPSec and N3 tunnelling
  • Enforcing QoS corresponding to N3 packet marking, taking into account QoS requirements associated to such marking received over N2
  • N3 user-plane packet marking in the uplink.
  • Local mobility anchor within untrusted non-3GPP access networks using MOBIKE per IETF RFC 4555 [57].
  • Supporting AMF selection.
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6.2.9A  TNGF [R16]
The functionality of TNGF in the case of trusted non-3GPP access includes the following:
  • Terminates the N2 and N3 interfaces.
  • Terminates the EAP-5G signalling and behaves as authenticator when the UE attempts to register to 5GC via the TNAN.
  • Implements the AMF selection procedure.
  • Transparently relays NAS messages between the UE and the AMF, via NWt.
  • Handles N2 signalling with SMF (relayed by AMF) for supporting PDU sessions and QoS.
  • Transparently relays PDU data units between the UE and UPF(s).
  • Implements a local mobility anchor within the TNAN.
  • Implements a local EAP Re-authentication (ER) server (as per RFC 6696) to facilitate mobility within the TNAN.
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6.2.10  AF
The Application Function (AF) interacts with the 3GPP Core Network in order to provide services, for example to support the following:
Based on operator deployment, Application Functions considered to be trusted by the operator can be allowed to interact directly with relevant Network Functions.
Application Functions not allowed by the operator to access directly the Network Functions shall use the external exposure framework (see clause 7.3) via the NEF to interact with relevant Network Functions.
The functionality and purpose of Application Functions are only defined in this specification with respect to their interaction with the 3GPP Core Network.
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6.2.11  UDRWord-p. 338
The Unified Data Repository (UDR) supports the following functionality:
  • Storage and retrieval of subscription data by the UDM.
  • Storage and retrieval of policy data by the PCF.
  • Storage and retrieval of structured data for exposure.
  • Application data (including Packet Flow Descriptions (PFDs) for application detection, AF request information for multiple UEs, 5GLAN group information for 5GLAN management).
  • Storage and retrieval of NF Group ID corresponding to subscriber identifier (e.g. IMPI, IMPU, SUPI).
The Unified Data Repository is located in the same PLMN as the NF service consumers storing in and retrieving data from it using Nudr. Nudr is an intra-PLMN interface.
NOTE 1:
Deployments can choose to collocate UDR with UDSF.
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6.2.12  UDSF
The UDSF is an optional function that supports the following functionality:
  • Storage and retrieval of information as unstructured data by any NF.
NOTE 1:
Structured data in this specification refers to data for which the structure is defined in 3GPP specifications. Unstructured data refers to data for which the structure is not defined in 3GPP specifications.
NOTE 2:
Deployments can choose to collocate UDSF with UDR.
6.2.13  SMSF
The SMSF supports the following functionality to support SMS over NAS:
  • SMS management subscription data checking and conducting SMS delivery accordingly.
  • SM-RP/SM-CP with the UE (see TS 24.011).
  • Relay the SM from UE toward SMS-GMSC/IWMSC/SMS-Router.
  • Relay the SM from SMS-GMSC/IWMSC/SMS-Router toward the UE.
  • SMS related CDR.
  • Lawful Interception.
  • Interaction with AMF and SMS-GMSC for notification procedure that the UE is unavailable for SMS transfer (i.e, notifies SMS-GMSC to inform UDM when UE is unavailable for SMS).
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6.2.14  NSSFWord-p. 339
The Network Slice Selection Function (NSSF) supports the following functionality:
  • Selecting the set of Network Slice instances serving the UE;
  • Determining the Allowed NSSAI and, if needed, the mapping to the Subscribed S-NSSAIs;
  • Determining the Configured NSSAI and, if needed, the mapping to the Subscribed S-NSSAIs;
  • Determining the AMF Set to be used to serve the UE, or, based on configuration, a list of candidate AMF(s), possibly by querying the NRF.
6.2.15  5G-EIR
The 5G-EIR is an optional network function that supports the following functionality:
  • Check the status of PEI (e.g. to check that it has not been blacklisted).
6.2.16  LMF
The functionality of LMF is defined in clause 4.3.8 of TS 23.273.
6.2.16A  GMLC [R16]
The functionality of GMLC is defined in clause 4.3.8 of TS 23.273.
6.2.17  SEPP
The Security Edge Protection Proxy (SEPP) is a non-transparent proxy and supports the following functionality:
  • Message filtering and policing on inter-PLMN control plane interfaces.
  • NOTE:
    The SEPP protects the connection between Service Consumers and Service Producers from a security perspective, i.e. the SEPP does not duplicate the Service Authorization applied by the Service Producers as specified in clause 7.1.4.
  • Topology hiding.
Detailed functionality of SEPP, related flows and the N32 reference point, are specified in TS 33.501.
The SEPP applies the above functionality to every Control Plane message in inter-PLMN signalling, acting as a service relay between the actual Service Producer and the actual Service Consumer. For both Service Producer and Consumer, the result of the service relaying is equivalent to a direct service interaction. Every Control Plane message in inter-PLMN signalling between the SEPPs may pass via IPX entities. More details on SEPPs and the IPX entities are described in TS 29.500 and TS 33.501.
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6.2.18  Network Data Analytics Function (NWDAF)
NWDAF represents operator managed network analytics logical function. The NWDAF includes the following functionality:
  • Support data collection from NFs and AFs;
  • Support data collection from OAM;
  • NWDAF service registration and metadata exposure to NFs/AFs;
  • Support analytics information provisioning to NFs, AF.
The details of the NWDAF functionality are defined in TS 23.288.
NOTE:
NWDAF functionality beyond its support for Nnwdaf is out of scope of 3GPP.
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6.2.19  SCP [R16]Word-p. 340
The Service Communication Proxy (SCP) includes one or more of the following functionalities. Some or all of the SCP functionalities may be supported in a single instance of an SCP:
  • Indirect Communication (see clause 7.1.1 for details).
  • Delegated Discovery (see clauses 7.1.1 and 6.3.1 for details).
  • Message forwarding and routing to destination NF/NF service.
  • Communication security (e.g. authorization of the NF Service Consumer to access the NF Service Producer API), load balancing, monitoring, overload control, etc.
  • Optionally interact with UDR, to resolve the UDM Group ID/UDR Group ID/AUSF Group ID/PCF Group ID/CHF Group ID/HSS Group ID based on UE identity, e.g. SUPI or IMPI/IMPU (see clause 6.3.1 for details).
NOTE 1:
Communication security, e.g. authorization of the NF Service Consumer to access the NF Service Producer's API is specified in TS 33.501.
NOTE 2:
Load balancing, monitoring, overload control functionality provided by the SCP is left up to implementation.
The SCP may be deployed in a distributed manner.
NOTE 3:
More than one SCP can be present in the communication path between NF Services.
SCPs can be deployed at PLMN level, shared-slice level and slice-specific level. It is left to operator deployment to ensure that SCPs can communicate with relevant NRFs.
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6.2.20  W-AGF [R16]
The functionality of W-AGF is specified in TS 23.316.
6.2.21  UE radio Capability Management Function (UCMF) [R16]
The UCMF is used for storage of dictionary entries corresponding to either PLMN-assigned or Manufacturer-assigned UE Radio Capability IDs. An AMF may subscribe with the UCMF to obtain from the UCMF new values of UE Radio Capability ID that the UCMF assigns for the purpose of caching them locally.
Provisioning of Manufacturer-assigned UE Radio Capability ID entries in the UCMF is performed from an AF that interacts with the UCMF either directly or via the NEF (or via Network Management) using a procedure defined in TS 23.502.
The UCMF also assigns the PLMN-assigned UE Radio Capability ID values.
Each PLMN-assigned UE Radio Capability ID is also associated to the TAC of the UE model(s) that it is related to. When an AMF requests the UCMF to assign a UE Radio Capability ID for a set of UE Radio Capabilities, it indicates the TAC of the UE that the UE Radio Capabilities are related to.
The UCMF stores a Version ID value for the PLMN assigned UE Radio Capability IDs so it is included in the PLMN assigned UE Radio Capability IDs it assigns. This shall be configured in the UCMF.
The UCMF may be provisioned with a dictionary of Manufacturer-assigned UE Radio Capability IDs which include a "Vendor ID" that applies to the Manufacturers of these UE, and a list of TACs for which the PLMN has obtained-Manufacturer-assigned UE Radio Capability IDs.
A PLMN-assigned UE Radio Capability IDs is kept in the UCMF storage as long as it is associated with at least a TAC value. When a TAC value is related to a UE model that is earmarked for operation based on Manufacturer assigned UE radio capability IDs, this TAC value is disassociated in the UCMF from any PLMN assigned UE Radio Capability IDs.
For the case that the PLMN is configured to store PLMN assigned IDs in the Manufacturer Assigned operation requested list defined in clause 5.11.3a 5.4.4.1a, the UCMF does not remove from storage any PLMN assigned UE radio Capability ID no longer used, and rather quarantines it to avoid any future reassignment.
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6.2.22  TWIF [R16]Word-p. 341
The functionality of Trusted WLAN Interworking Function (TWIF) is specified in clause 4.2.8.5.3.

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