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full Contents for  TS 23.501  Word version:   16.4.0

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1…   3…   4…   4.2.4   4.2.5…   4.2.8………   4.2.9…   4.3…   4.3.3   4.3.4   4.3.5   4.4…   4.4.6…   4.4.8   5…   5.3…   5.3.3…   5.4…   5.5…   5.6…   5.6.7…   5.7…   5.7.2…   5.7.3…   5.7.4   5.7.5…   5.8……   5.9…   5.10…   5.11…   5.15…   5.16…   5.17…   5.18…   5.19…   5.21…   5.22…   5.27…   5.28…   5.29…   5.30…   5.31…   5.32…   5.33…   5.34…   5.35…   6…   6.3…   7…   7.2…   8…   8.2.4   8.2.5…   8.3…   A…   D…   E…   F   G…   G.3   G.4…   J…


4  Architecture model and conceptsWord-p. 29
4.1  General concepts
The 5G System architecture is defined to support data connectivity and services enabling deployments to use techniques such as e.g. Network Function Virtualization and Software Defined Networking. The 5G System architecture shall leverage service-based interactions between Control Plane (CP) Network Functions where identified. Some key principles and concept are to:
  • Separate the User Plane (UP) functions from the Control Plane (CP) functions, allowing independent scalability, evolution and flexible deployments e.g. centralized location or distributed (remote) location.
  • Modularize the function design, e.g. to enable flexible and efficient network slicing.
  • Wherever applicable, define procedures (i.e. the set of interactions between network functions) as services, so that their re-use is possible.
  • Enable each Network Function and its Network Function Services to interact with other NF and its Network Function Services directly or indirectly via a Service Communication Proxy if required. The architecture does not preclude the use of another intermediate function to help route Control Plane messages (e.g. like a DRA).
  • Minimize dependencies between the Access Network (AN) and the Core Network (CN). The architecture is defined with a converged core network with a common AN - CN interface which integrates different Access Types e.g. 3GPP access and non-3GPP access.
  • Support a unified authentication framework.
  • Support "stateless" NFs, where the "compute" resource is decoupled from the "storage" resource.
  • Support capability exposure.
  • Support concurrent access to local and centralized services. To support low latency services and access to local data networks, UP functions can be deployed close to the Access Network.
  • Support roaming with both Home routed traffic as well as Local breakout traffic in the visited PLMN.
4.2  Architecture reference model
4.2.1  General
This specification describes the architecture for the 5G System. The 5G architecture is defined as service-based and the interaction between network functions is represented in two ways.
  • A service-based representation, where network functions (e.g. AMF) within the Control Plane enables other authorized network functions to access their services. This representation also includes point-to-point reference points where necessary.
  • A reference point representation, shows the interaction exist between the NF services in the network functions described by point-to-point reference point (e.g. N11) between any two network functions (e.g. AMF and SMF).
Service-based interfaces are listed in clause 4.2.6. Reference points are listed in clause 4.2.7.
Network functions within the 5GC Control Plane shall only use service-based interfaces for their interactions.
The interactions between NF services within one NF are not specified in this Release of the specification.
UPF does not provide any services in this Release of the specification, but can consume services provided by 5GC Control Plane NFs.
NFs and NF services can communicate directly, referred to as Direct Communication, or indirectly via the SCP, referred to as Indirect Communication. For more information on communication options, see Annex E and clauses under 6.3.1 and 7.1.2.
4.2.2  Network Functions and entitiesWord-p. 30
The 5G System architecture consists of the following network functions (NF).
  • Authentication Server Function (AUSF)
  • Access and Mobility Management Function (AMF)
  • Data Network (DN), e.g. operator services, Internet access or 3rd party services
  • Unstructured Data Storage Function (UDSF)
  • Network Exposure Function (NEF)
  • Intermediate NEF (I-NEF)
  • Network Repository Function (NRF)
  • Network Slice Selection Function (NSSF)
  • Policy Control Function (PCF)
  • Session Management Function (SMF)
  • Unified Data Management (UDM)
  • Unified Data Repository (UDR)
  • User Plane Function (UPF)
  • UE radio Capability Management Function (UCMF)
  • Application Function (AF)
  • User Equipment (UE)
  • (Radio) Access Network ((R)AN)
  • 5G-Equipment Identity Register (5G-EIR)
  • Network Data Analytics Function (NWDAF)
  • CHarging Function (CHF)
The functional description of the CHF is specified in TS 32.240.
The 5G System architecture also comprises the following network entities:
  • Service Communication Proxy (SCP)
  • Security Edge Protection Proxy (SEPP)
The functional descriptions of these Network Functions and entities are specified in clause 6.
  • Non-3GPP InterWorking Function (N3IWF)
  • Trusted Non-3GPP Gateway Function (TNGF)
  • Wireline Access Gateway Function (W-AGF)
  • Trusted WLAN Interworking Function (TWIF)
4.2.3  Non-roaming reference architecture
Figure 4.2.3-1 depicts the non-roaming reference architecture. Service-based interfaces are used within the Control Plane.
If an SCP is deployed it can be used for indirect communication between NFs and NF services as described in Annex E. SCP does not expose services itself.
Figure 4.2.3-2 depicts the 5G System architecture in the non-roaming case, using the reference point representation showing how various network functions interact with each other.
N9, N14 are not shown in all other figures however they may also be applicable for other scenarios.
For the sake of clarity of the point-to-point diagrams, the UDSF, NEF and NRF have not been depicted. However, all depicted Network Functions can interact with the UDSF, UDR, NEF and NRF as necessary.
The UDM uses subscription data and authentication data and the PCF uses policy data that may be stored in UDR (refer to clause 4.2.5).
For clarity, the UDR and its connections with other NFs, e.g. PCF, are not depicted in the point-to-point and service-based architecture diagrams. For more information on data storage architectures refer to clause 4.2.5.
For clarity, the NWDAF and its connections with other NFs, e.g. PCF, are not depicted in the point-to-point and service-based architecture diagrams. For more information on network data analytics architecture refer to TS 23.288.
Figure 4.2.3-3 depicts the non-roaming architecture for UEs concurrently accessing two (e.g. local and central) data networks using multiple PDU Sessions, using the reference point representation. This figure shows the architecture for multiple PDU Sessions where two SMFs are selected for the two different PDU Sessions. However, each SMF may also have the capability to control both a local and a central UPF within a PDU Session.
Figure 4.2.3-4 depicts the non-roaming architecture in the case of concurrent access to two (e.g. local and central) data networks is provided within a single PDU Session, using the reference point representation.
Figure 4.2.3-5 depicts the non-roaming architecture for Network Exposure Function, using reference point representation.
In Figure 4.2.3-5, Trust domain for NEF is same as Trust domain for SCEF as defined in TS 23.682.
In Figure 4.2.3-5, 3GPP Interface represents southbound interfaces between NEF and 5GC Network Functions e.g. N29 interface between NEF and SMF, N30 interface between NEF and PCF, etc. All southbound interfaces from NEF are not shown for the sake of simplicity.

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