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dsTest 5G Core Network Testing

The suite of applications for 5G Core Network testing is under development at Developing Solutions. We will start releasing native applications to test your service-based interfaces soon along with applications to test the UE Control Plane and User Plane reference point interfaces (N1/N2, N3, and N4). Our product pages will keep you apprised of application availability as we release new applications. In the mean time, our REST ServiceFlow application is currently available, and you can use it to test any service-based interface.

We are also developing 5G reference materials to assist with your testing activities. Use our 5G Service Map to locate Stage 3 specifications, translate between service-based interfaces and architectural reference points, and identify the network functions that produce and consume services. Furthermore, we will be publishing a protocol dictionaries in the near future. The diagrams and definitions below provide an overview of the 5G Core Network and network element functions.

5G Core Network Reference Point Diagram

5GC Reference Point Architecture


5GC Service-Based Interface Diagram

RESTful Service-Based Interfaces in the 5GC

5G Equipment Identity Register (EIR)

The 5G-EIR maintains a list of blacklisted permanent equipment identities and provides that information to the AMF upon request.

Access and Mobility Management Function (AMF)

The AMF terminates the NG RAN and N3IWF control plane interfaces (N2) and UE NAS ciphering and integrity protection (N1). It also provides transport for messages between core network functions such as SMS, PCF, or location management and the UE. In addition, the AMF is generally responsible for access authentication and authorization while managing UE registration, connection, reachability, mobility, and the enforcement of access-related and mobility-related policies.

Application Function (AF)

An AF provides application services to the subscriber. It may interact with the PCF in order to influence traffic routing, to notify the PCF of application bandwidth requirements or usage thresholds, or to register for PDU session events. If an AF is trusted it can interact directly with the PCF; otherwise it must interact with an NEF.

Authentication Server Function (AUSF)

The only responsibility of the AUSF is UE authentication for 3GPP network access and for access from untrusted, non-3GPP WLANs.

Binding Support Function (BSF)

The BSF stores the associations between UEs, data networks, and serving PCFs for specific PDU sessions. Any NF can thereby quickly retrieve the PCF associated with a PDU session. An external AF may retrieve a binding via the NEF. The PCF registers, updates, and removes the stored bindings as indicated by session events. A BSF may be standalone or collocated with other network functions (e.g., PCF, UDR, NRF, SMF).

Charging Function (CHF)

In contrast to the separate online and offline charging functions in 4G networks, 5G introduces the Converged Charging System (CCS). The CHF is the interface between the CCS and the 5GC. It provides spending limits and quotas for services to the PCF and SMF and collects usage information from the SMF.

Gateway Mobile Location Center (GMLC)

The GMLC interacts with external Location Services (LCS) clients via the Le interface (not shown above), providing them with the current location of specified UEs. If the GMLC implements the Location Retrieval Function (LRF) it learns the identity of the UE’s serving AMF from the UDM and then obtains the UE’s location from that AMF. The LRF can alternatively be a standalone node that provides services to multiple GMLCs.

gNodeB (gNB)

Access to the 5GC from the NG RAN is established through the gNodeB. It terminates the N1/N2 interface with the AMF and the N3 interface with the UPF. In addition, it is responsible for AMF selection when the requisite information is not available from the UE.

Location Management Function (LMF)

The LMF determines, using information from the UE and/or NG RAN, the current location of the UE and provides it on request.

Network Data Analytics Function (NWDAF)

The NSSF may use network load information during slice selection and the PCF may also use that information when it formulates dynamic policy rules. The NWDAF provides load information at the network slice instance level on request and via notification to subscribed NFs.

Network Exposure Function (NEF)

The NEF exposes network capabilities and events to other network functions within the 5GC and also provides a secure means for external application functions to interact with core network functions like the PCF. Any NF in the 5GC can interact with an NEF. When dealing with external entities the NEF can mask sensitive network and user information. Furthermore, an NEF may manage packet flow descriptions — operating as a PFDF — and either provide PFDs to the SMF on request or push PFDs to the SMF as part of the management function.

Network Repository Function (NRF)

5G expands the concept of service discovery with the NRF. Any network function can query an NRF to obtain the identities and locations of other network functions that provide a specific service. Multiple NRFs may be deployed in a network and they may be deployed at different levels — providing information about the entire network, about a set of network slices, or about a network slice instance.

Network Slice Selection Function (NSSF)

One of the most noteworthy innovations in the 5GC is the introduction of the network slice — a set of logically separated NFs that provide full PLMN services. The NSSF selects the set of network slice instance(s) that will serve a UE. The selection process is informed by subscription data and network load information. In a dynamic network the NSSF may query the NRF to discover service producers.

Non-3GPP Interworking Function (N3IWF)

The N3IWF provides access to the 5GC from untrusted, non-3GPP WLANs. It establishes and terminates an IPSec tunnel with the UE and terminates the N1/N2 and N3 interfaces with the 5GC. Similar to the gNodeB, the N3IWF relays N1/N2 signalling between the UE and the AMF as well as relaying user plane packets between the UE and the UPF.

Policy Control Function (PCF)

The PCF primarily determines which rules will govern UE session management and user plane traffic, including authorized QoS, gating rules, and traffic steering control. The AMF utilizes access and mobility rules. while session management rules are used by the SMF. The UPF receives rules for service data flows and PDU sessions via the SMF. The PCF also conveys to the UE, via the AMF, how the UE will route outgoing traffic. The policy decisions made by the PCF may be based on subscription information obtained from the UDR along with information regarding the current load on network slices from the NWDAF and, potentially, online charging information from the CHF.

If an AF specifies a usage threshold for the session — whether it’s a P-CSCF in IMS or an external AF — the PCF may invoke usage monitoring on the SMF and may notify the AF when a threshold is reached. An AF can also register for session event notification from the PCF or request the PCF to report access network information (when Rx is supported). When the AF is an external entity it interacts with the PCF via the NEF.

Session Management Function (SMF)

The SMF is primarily concerned with managing the UE’s PDU sessions. Its responsibilities include the establishment, modification, and release of the PDU sessions along with maintenance of the tunnel (N3) between the UPF and the gNodeB or N3IWF. The SMF selects the UPF that will handle the session’s user plane traffic and configures traffic steering at that UPF. It also handles UE IP address allocation and DHCP services as well as determining the session and service continuity (SSC) mode for the UE’s session. Finally, in the policy and charging arena the SMF enforces policy decisions related to charging, pushes rules regarding traffic handling and reporting to the UPF, and collects usage data that is then reported to the CHF.

Short Message Service Function (SMSF)

The SMSF manages short message service over NAS and implements SM-RP/SM-CP with the UE. It relays MO messages toward the SMS Router and relays MT messages toward the UE. It also interacts with the AMF regarding availability of the UE for SMS transfer.

Unified Data Management (UDM)

UDM services provide subscriber, session, and subscription information — user identifiers and authentication credentials, serving NF identifiers, access authorization — to various network functions. The UDM also manages subscription data and may store this information itself or manage the information stored in a UDR.

Unified Data Repository (UDR)

The UDR provides storage and retrieval services for structured data in the PLMN. The UDR stores subscription data used by the UDM and the PCF, application data (including PFDs) used by the NEF, and data to be exposed by the NEF.

User Plane Function (UPF)

In keeping with the control and user plane separation (CUPS) architecture, the UPF is solely concerned with handling user data. This includes routing, forwarding, downlink packet buffering, ARP and IPv6 neighbor solicitation proxying, and packet inspection. The SMF informs the UPF of the policies that it must enforce. The UPF, in turn, reports the traffic usage data that it collects to the SMF.