3. 3GPP 5GC (the only specification for a 5G mobile packet core)
3
3GPP’s 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.
4. 3GPP 5GC (the only specification for a 5G mobile packet core)
4
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.
The 5G architecture is defined as service-based and the interaction between network
functions is represented in the following two ways:
A service-based representation(SBA), 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).
5. 3GPP 5G Core Network Standard
5
Rel-15 5GS Phase1 Features
Feature Category Detailed Function
Architectural enablers
for virtualized
deployment
Network
Architecture
§ Service based architecture with service-based interfaces
§ Data Storage architecture enabling Compute and Storage
separation
§ Support for AMF resiliency (e.g., AMF change with no
service disruption)
Enablers for new
business opportunity
New
Enhancement
§ E2E Network Slicing
§ Support for edge computing and URLLC services
§ Local Area Data Network for specialized service
Synergy with pre-
installed LTE/Wi-Fi
Multi-RAT
Support
§ Interworking with LTE/EPC
§ Common interface for 3GPP and non-3GPP access
Dynamic and finer
control of QoS
QoS Control
§ Flow-based QoS framework
§ Reflective QoS
Differentiated mobility
control for variety of
devices
Mobility
Management
§ Mobility restriction per UE
§ Support for RRC inactive and MICO* mode
Flexible and optimized
network utilization
Session
Management
§ Session model supporting ‘Session and Service
Continuity’ modes
§ Concurrent (e.g. local and central) access to a data
network
§ Application influence on traffic routing
6. 5G Core Implementation
6
Unlike previous cellular generations, 5G implementation is based on:-
• Cloud-native applications.
• REST services-based integration.
• Virtualized Network Functions.
• Softwarization of Network & IT.
• Support for Stateless Network functions by decoupling Compute and Storage.
• Microservices based design patterns.
• DevOps, CI/CD methodologies for faster time-to-market offerings.
• Network slice-based approach of utilizing the physical network resources.
• Mobile access edge computing for delivering & processing low latency contents & data.
• Providing cellular connections to things & devices and supporting very high density.
• Handling advanced analytics.
• Separation of Control & User planes.
• Network capability exposure via APIs and Service Bus.
• Support for Centralized and Distributed processing.
• etc.
8. 5G Core Evolution
8
Functional entities
Single Core
Dedicated protocols
Service Based (SBA/SBI/NAPS)
Virtualization & Slicing
Softwarization/ Cloudification
Application Programming Interfaces
Harmonized protocols (HTTP …)
Exposure to 3rdParties
Backward & Forward Compatibility
5G
9. Deployment Scenario in South Korea Operator(KT and SK)
32
The 5G NSA core network can be 2 or 3 in the figure below. In case of KT, it
corresponds to 3. SK Telecom and LG U+ correspond to 2.
10. Functional blocks within 5G Core Network Architecture
10
AUSF = Authentication Server Function
UDM = Unified Data Management
NSSF = Network Slice Selection Function
NEF = Network Exposure Function
NRF = Network Repository Function
AMF = Core Access and Mobility Management Function
SMF = Session Management Function
PCF = Policy Control Function
AF = Application Function
UE = User Equipment
RAN = Radio Access Network
CU = Centralised Unit
DU = Distributed Unit
UPF = User Plane Function
DN = Data Network, e.g. operator services, Internet or 3rd party services
11. NR Reference Point System Architecture
11
Control Plane Entities
User Plane Entities
AMF : - Core Access and Mobility Management
Function
UPF : - User plane Function
SMF : - Session Management Control Function .
DN : - Data Network (DN)
NSSF : - Network Slice Selection Function.
AUSF : - Authentication Server
Function
UDM : - Unified Data Management.
PCF : - Policy Control Function.
AF : - Application Function.
The Reference point Architecture is based upon a set of Network Elements.
Reference Point Architecture uses point to point interfaces to interconnect those Network Elements.
Signaling Procedures are specified between each point to point interface.
LTE NW Architecture is an example of Reference Point Architecture.
Network Function Spit for Flexible Network
§ Flexibility : AMF-SMF Split, CP-UP Separation
§ New I/F’s : AMF/SMF - Policy Function, AMF/SMF - Subscription DB
§ New NF’s : NSSF for Slice Selection, AUSF for EAP framework
12. 5G interfaces (reference points)
12
NG1: Reference point between the UE and the Access and Mobility Management function
NG2: Reference point between the gNB and the Access and Mobility Management function
NG3: Reference point between the gNB and the User plane function (UPF)
NG4: Reference point between the Session Management function (SMF) and the User plane
function (UPF)
NG5: Reference point between the Policy Function (PCF) and an Application Function (AF)
NG6: Reference point between the User Plane function (UPF) and a Data Network (DN)
NG7: Reference point between the Session Management function (SMF) and the Policy Control
function (PCF)
NG8: Reference point between Unified Data Management and AMF
NG9: Reference point between two Core User plane functions (UPFs)
NG10: Reference point between UDM and SMF
NG11: Reference point between Access and Mobility Management function (AMF) and Session
Management function (SMF)
NG12: Reference point between Access and Mobility Management function (AMF) and
Authentication Server function (AUSF)
NG13: Reference point between UDM and Authentication Server function (AUSF) NG14: Reference
point between 2 Access and Mobility Management function (AMF)
NG15: Reference point between the PCF and the AMF in case of non-roaming scenario, V-PCF and
AMF in case of roaming scenario
13. Service Based Architecture(SBA) Network
13
The most outstanding change in the 5G Core Control plane is induction of Service
based Interface (SBI) or Service based Architecture (SBA) from traditional Point-to-Point
network architecture. With this new change, except for a few interfaces such as N2 and
N4, almost every interface is now defined to use unified interface, using HTTP/2
protocol.
Service based architecture is based on
a set Network Functions (NFs)
NFs provides services to other NFs
Service Base Interface (SBI)
Reference Point interface is replaced
by a common bus to connect all NFs
14. Service Based Architecture(SBA) Network
14
Service Based Architecture is applicable to the control plane only.
The user plane still remains Point to Point only.
All the functions connect to the Bus- there is no point to point interface defined now.
There is a common bus and through this bus all the Network Functions connect.
The HOD of all the functions is Network Function Repository Function (NRF).All the
Functions give their attendance to NRF saying – that I am a function A and I give this
service. If any Function need any service it will ask NRF- who gives this service, so NRF
contain details of all Network Elements and what all functions they give.
Most likely all the Operators will go for Service Based Architecture and not for
Reference Point Architecture.
In Service based Architecture we have a common bus.
The Nodes are called Network Functions
In SBA, Network Functions (NFs) capabilities are exposed via REST APIs and based out
of HTTP2.0 protocol.
Interconnection between NFs can be based on the Request/Response model or
Subscribe/Notify model for availing the different 5G Services.
15. Service Based Architecture Network
38
NG UE
N2
N3 N6
N4
5G
RAN UPF
SMF
AUSF
N1
AMF
AF
Namf
Nausf
Npcf
Nsmf
Naf
Data Network
(e.g. operator
or Internet)
NRF UDM PCF
Nnrf Nudm
NEF
Nnef
§ AF: Application Function
§ AMF: Access and Mobility Management
Function
§ AUSF: Authentication Server Function
§ NEF: Network Exposure Function
§ NRF: Network Repository Function
§ PCF: Policy Control Function
§ SMF: Session Management Function
§ UDM: Unified Data Management
§ UPF.: User Plane Function
Network Functions within the 5GC Control Plane (CP) use Service-Based Interfaces
(SBI) for their interactions:
A CP NF can provide one or more NF Services
All interactions are abstracted as: Request-Response, Subscription-Notify System
procedures are described as a sequence of NF service invocations
Control Plane
User Plane
Network Function(NF)
SBI
SBI BUS
16. Mapping NG Core and EPC
16
S1-U S5
S11
PCRF
Gx
PGW
SGW
S1-MME MME S6a HSS
SGi
MME
S1-MME
S1-U
S11
HSS PCRF
Gx
S6a
SGi
AfterCUPS
SGW
CP
PGW
CP
SGW
UP
PGW
UP
Mapping the EPC
functions to new
5G CN functions
N3 N6
N4
SMF
PCF
AUSF UDM
N13
N12 N10 N7
N15
Access &
Mobility
managemen
N
tG11
Functio
A
n
M
(
F
AMF)
MME
User Plane
Functio
U
n
PF
(UPF)
PGW SGW
UP UP
PolicyControl
Function(PCF)
PCRF
Session
Management
Function(SMF)
SGW PGW
CP CP
MME
Authentication Server
Function (AUSF) and User
Data Management(UDM)
HSS/
AAA
N8
17. 5GC Network Entities Functions
17
AMF Function : The AMF performs most of the functions that the MME performs in
a 4G network.
§ Termination point for RAN CP interfaces (N2)
§ UE Authentication & Access Security.
§ Mobility Management (Reachability, Idle/Active Mode mobility state handling)
§ Registration Area management;
§ Access Authorization including check of roaming rights;
§ Session Management Function (SMF) selection
§ NAS signaling including NAS Ciphering and Integrity protection, termination of MM NAS and
forwarding of SM NAS (N1).
§ AMF obtains information related to MM from UDM.
§ May include the Network Slice Selection Function (NSSF)
§ Attach procedure without session management adopted in CIoT implemented in EPC is
defined also in 5GCN (registration management procedure)
§ User Plane (UP) selection and termination of N4 interface (AMF has part of the MME and
PGW functionality from EPC)
18. 5GC Network Entities Functions
18
SMF Function : The SMF performs the session management functions that are
handled by the 4G MME, SGW-C, and PGW-C.
§ Allocates IP addresses to UEs
§ NAS signaling for session management (SM)
§ Sends QoS and policy information to RAN via the AMF
§ Downlink data notification
§ Select and control UPF for traffic routing. The UPF selection function enables Mobile Edge
Computing (MEC) by selecting a UPF close to the edge of the network.
§ Acts as the interface for all communication related to offered user plane services. SMF
determines how the policy and charging for these services is applied.
§ Lawful intercept – control Plane
PCF Function : The 5G PCF performs the same function as the PCRF in 4G networks.
§ Provides policy rules for control plane functions. This includes network slicing, roaming and
mobility management.
§ Accesses subscription information for policy decisions taken by the UDR. Supports the new 5G
QoS policy and charging control functions.
AUSF Function : The AUSF performs the authentication function of 4G HSS.
§ Implements the EAP authentication server
§ Stores keys
19. 5GC Network Entities Functions
19
UPF Function : The UPF is essentially a fusion of the data plane parts of the SGW and
PGW. In the context of the CUPS architecture: EPC SGW-U + EPC PGW-U → 5G UPF .
The UPF performs the following functions:
§ Packet routing and forwarding
§ Packet inspection and QoS handling. The UPF may optionally integrate a Deep Packet Inspection
(DPI) for packet inspection and classification. The following figure shows the classification and
QoS handling at the UPF
§ Connecting to the Internet POP (Point of Presence). The UPF may optionally integrate the Firewall
and Network Address Translation (NAT) functions.
§ Mobility anchor for Intra RAT and Inter-RAT handovers Lawful intercept — user plane
Maintains and reports traffic statistics
UDM Function : The UDM performs parts of the 4G HSS function.
§ Generation of Authentication and Key Agreement (AKA) credentials
§ User identification
§ Access authorization
§ Subscription management
21. 5G with CUPS
21
Data Network
(e.g. operator
or Internet)
NR UE
N
2
N3 N6
gNB UPF
AMF
NR Uu
Reconfiguring LTE network functions.
Support for native CUPS.
Virtualized NFs on commodity hardware based architecture.
Distributed UPFs to edge to reduce latency and backhaul traffic.
Enabling standard – based MEC by supporting routing to local UPFs located at edge sites.
CUPS extended to RAN
Enabling E2E network slicing by supporting independent parts for each service.
N11
5GC
SMF
N4
R
U
D
U
C
U
MME MME + GW-C
GW-U
NG RAN
