Advanced: 5G Service Based Architecture (SBA)

5G Service Based
Architecture (SBA)
@3g4gUK

EPC before CUPS
©3G4G
Data (IP)
Network
eNodeB
MME
UE
S-GW
P-GW
EPC
S1-MMES1-U
S11
SGi
HSS
S6a
PCRFTDF
SGi Gx
S5/S8

EPC after CUPS
©3G4G
Data (IP)
Network
eNodeB
MME
UE
S-GW-C
P-GW-C
EPC
S1-MMES1-U
S11
SGi
HSS
S6a
PCRFTDF-U
SGi Gx
S5/S8-C
P-GW-U
S-GW-UTDF-C
S5/S8-U
Sxb
Sxa
Sxc

2G – 4G Reference Point Network Architecture
©3G4G
BSC
BTS
MSC
Voice (PSTN)
Network
SGSN
Data (IP)
Network
RNC
Node BeNodeB
MME
GGSN
Access
Network
Core
Network
Air
Interface
MSUEUE
BSSRNS
S-GW
P-GW
2G 2.5G
3G 4G
EPC

5GS Reference Point Representation
©3G4G

5GS Service Based Architecture (SBA)
©3G4G

SBA Terminology
©3G4G
Source: Georg Mayer
NF – Network Function
SBI – Service Based Interface
SBA – Service Based Architecture

Core Network Architecture Evolution in 5G
©3G4G
• 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
Source: Georg Mayer

Control plane
function group
©3G4G
gNodeB
(NG-RAN)
5G UE
User plane
function

Control plane
function group
©3G4G
gNodeB
(NG-RAN)
5G UE
User plane
function
UPF
N3

User Plane Function (UPF)
©3G4G
• The U-plane function (UPF) in the 5G core network provides functions specific to
U-plane processing the same as S-GW-U and P-GW-U in CUPS.
• See section 6.2.3 of TS 23.501 for more details on functionality of UPF
CUPS Architecture

User Plane Function (UPF)
©3G4G
• Section 6.2.3 of TS 23.501 - 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).
• 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).
• 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.
• ARP proxying as specified in IETF RFC 1027 and / or IPv6 Neighbour Solicitation Proxying as specified in IETF RFC 4861 functionality 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.
NOTE:Not all of the UPF functionalities are required to be supported in an instance of user plane function of a Network Slice.

User plane
function
UPF
Control plane
function group
©3G4G
Data Network
(DN)gNodeB
(NG-RAN)
5G UE
N3 N6

Control plane
function group
©3G4G
5G UE
SMF
N4
User plane
function
UPF Data Network
(DN)gNodeB
(NG-RAN)
N3 N6

Session Management Function (SMF)
©3G4G
• The control plane functionality has been slightly re-organized in 5G
core network. Instead of MME, S-GW-C & P-GW-C in EPC, the
functionality has been divided between Session Management
Function (SMF) and Access & Mobility management Function.
• There can be multiple SMFs associated with the UE. One for each
slice.
• See section 6.2.2 of TS 23.501 for more details on functionality of
SMF
CUPS Architecture

©3G4G
• Section 6.2.2 of TS 23.501 - 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).
• DHCPv4 (server and client) and DHCPv6 (server and client) functions.
• ARP proxying as specified in IETF RFC 1027 [53] and / or IPv6 Neighbour Solicitation Proxying as specified in IETF RFC 4861 [54] functionality 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.
• 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.

©3G4G
• 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 authorization/authentication by external DN.
NOTE:Not all of the functionalities are required to be supported in a 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.

Control plane
function group
©3G4G
Data Network
(DN)gNodeB
(NG-RAN)
5G UE
User plane
function
UPF
AMF SMF
N1
N2
N3 N6
N4

Access & Mobility management Function (AMF)
©3G4G
• AMF is a single node to manage all UE related functions.
• The EPC functionality of MME, S-GW-C & P-GW-C has been
reallocated so that all access and mobility functionality is done by
AMF
• See section 6.2.1 of TS 23.501 for more details on functionality of
AMF
CUPS Architecture

©3G4G
Section 6.2.1 of TS 23.501 - 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). It interacts with the AUSF and the UE, receives the intermediate key that was established as a result of the UE
authentication process. In case of USIM based authentication, the AMF retrieves the security material from the AUSF.
• Security Context Management (SCM). The SCM receives a key from the SEAF that it uses to derive access-network specific keys.
• 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.
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.

©3G4G
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. Over this interface, some information (e.g. 3GPP cell Identification) and procedures (e.g. Hand-Over 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. 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.
• Management of mobility, authentication, and separate security context state(s) of a UE connected via non-3GPP access or connected via 3GPP and non-
3GPP accesses simultaneously.
• Support as described in clause 5.3.2.3 a co-ordinated RM management context valid over 3GPP and Non 3GPP accesses.
• 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

Control plane
function group
©3G4G
Data Network
(DN)gNodeB
(NG-RAN)
5G UE
User plane
function
UPF
AMF SMF
NSSF
N1
N2
N3 N6
N4
Nnssf

Network Slice Selection Function (NSSF)
©3G4G
• NSSF supports the following functionality:
• Selecting the set of Network Slice instances serving the UE,
• Determining the Allowed NSSAI (Network Slice Selection
Assistance Information) 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.
CUPS Architecture

Network Slice Selection Function (NSSF)
©3G4G
Section 6.2.14 of TS 23.501 - 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 AMF Set to be used to serve the UE, or, based on configuration, a list of candidate AMF(s), possibly by querying the NRF.

Control plane
function group
©3G4G
Data Network
(DN)gNodeB
(NG-RAN)
5G UE
User plane
function
UPF
AMF SMF
NSSF NEF
N1
N2
N3 N6
N4
Nnssf Nnef

Network Exposure Function (NEF)
©3G4G
• A Network Exposure Function (NEF) having a
function similar to the Service Capability Exposure
Function (SCEF) in EPC.
• See section 6.2.5 of TS 23.501 for more details on
functionality of NEF
CUPS Architecture

Network Exposure Function (NEF)
©3G4G
Section 6.2.5 of TS 23.501 - The Network Exposure Function (NEF) supports the following independent functionality:
• Exposure of capabilities and events:
3GPP NFs expose capabilities and events to other NFs via NEF. NF exposed capabilities and events may be securely exposed 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).
NOTE:The NEF can access the UDR located in the same PLMN as the NEF.
• 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. 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) (interface to be defined by 3GPP).
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 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.

Control plane
function group
©3G4G
Data Network
(DN)gNodeB
(NG-RAN)
5G UE
User plane
function
UPF
AMF SMF
NSSF NEF NRF
N1
N2
N3 N6
N4
Nnssf Nnef Nnrf

Network Repository Function (NRF)
©3G4G
• Different Network Functions (NFs) are connected together via a uniform
interface called a service-based interface. In addition, an individual NF
consists of smaller unit functions called NF services, and an NF service in a
certain NF can directly access an NF service in another NF without having to
pass through another node. A Network Repository Function (NRF)
provides a discovery function for NF services.
• See section 6.2.6 of TS 23.501 for more details on functionality of NRF
CUPS Architecture

©3G4G
Section 6.2.6 of TS 23.501 - The NF Repository Function (NRF) supports the following functionality:
• Supports service discovery function. Receive NF Discovery Request from NF instance, and provides the information of the discovered NF instances (be
discovered) to the NF instance.
• Maintains the NF profile of available NF instances and their supported services.
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 Specific Service authorization information
• Names of supported services
• Endpoint information of instance(s) of each supported service
• Identification of stored data/information
NOTE 1: 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, notification endpoint for each type of notification that the NF service is interested in receiving.
NOTE 2: It is expected service authorization information is usually provided by OA&M system, and it can also be included in the NF profile in case that
e.g. an NF instance has an exceptional service authorization information.

©3G4G
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).
NOTE 3: Whether NRF is an enhancement of DNS server is to be determined during Stage 3.
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

Control plane
function group
©3G4G
Data Network
(DN)gNodeB
(NG-RAN)
5G UE
User plane
function
UPF
AMF SMF
NSSF NEF NRF UDM
UDR
FE
N1
N2
N3 N6
N4
Nnssf Nnef Nnrf Nudm

Unified Data Repository (UDR)
©3G4G
• UDR is a facility where user data can be accessed
stored and managed in a common way.
functionality of UDR
CUPS Architecture

Unified Data Repository (UDR)
©3G4G
Section 6.2.11 of TS 23.501 - 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, and application data (including Packet Flow Descriptions (PFDs) for application detection,
application request information for multiple UEs), by the NEF.
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.
Section 6.2.12 of TS 23.501 - The UDSF (Unstructured Data Storage Function) is an optional function that supports the following functionality:
• Storage and retrieval of information as unstructured data by any NF.
NOTE:Deployments can choose to collocate UDSF with UDR.

Front End (FE)
©3G4G
• Front End (FE) is a core network functional entity or
service layer entity or provisioning entity that can access
user data stored in a unique repository.
• Front End Identifier is defined as a name that uniquely
identifies an FE within the set of all FEs accessing an UDR.
CUPS Architecture

Unified Data Management (UDM)
©3G4G
• Unified Data Management (UDM), is analogous to the Home Subscriber Server (HSS)
in EPC architecture and introduces the concept of User Data Convergence (UDC) that
separates the User Data Repository (UDR) storing and managing subscriber in-
formation from the front end processing subscriber information.
• See section 6.2.7 of TS 23.501 for more details on functionality of UDM
CUPS Architecture

Unified Data Management (UDM)
©3G4G
Section 6.2.7 of TS 23.501 - 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).
• 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.
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 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.

Control plane
function group
©3G4G
Data Network
(DN)gNodeB
(NG-RAN)
5G UE
User plane
function
UPF
AMF SMF
NSSF NEF NRF AUSFFEUDM
UDR
FE
N1
N2
N3 N6
N4
Nnssf Nnef Nnrf Nudm Nausf

Authentication Server Function (AUSF)
©3G4G
• The front-end section includes new specifications
for an Authentication Server Function (AUSF)
dedicated to authentication processing
functionality of AUSF
CUPS Architecture

Authentication Server Function (AUSF)
©3G4G
Section 6.2.8 of TS 23.501 - The AUSF supports the following functionality:
• Supports Authentication Server Function (AUSF) as specified by SA WG3.

Control plane
function group
©3G4G
Data Network
(DN)gNodeB
(NG-RAN)
5G UE
User plane
function
UPF
AMF SMF
NSSF NEF NRF AUSFFE PCFFEUDM
UDR
FE
N1
N2
N3 N6
N4
Nnssf Nnef Nnrf Nudm Nausf Npcf

Policy Control Function (PCF)
©3G4G
• The front-end section includes new specifications
for a Policy Control Function (PCF) corresponding to
the Policy and Charging Rule control Function (PCRF)
in EPC.
functionality of PCF
CUPS Architecture

Policy Control Function (PCF)
©3G4G
Section 6.2.4 of TS 23.501 - 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.

Control plane
function group
©3G4G
Data Network
(DN)gNodeB
(NG-RAN)
5G UE
User plane
function
UPF
AMF SMF
NSSF NEF NRF AUSFFE PCFFEUDM
UDR
FE
UDC
N1
N2
N3 N6
N4
Nnssf Nnef Nnrf Nudm Nausf Npcf

User Data Convergence (UDC)
©3G4G
• User data convergence is an optional concept to ensure data consistency and
simplify creation of new services by providing easy access to the user data, as well
as to ensure the consistency of storage and data models and to have minimum
impact on traffic mechanisms, reference points and protocols of network
elements.
• See 3GPP TS 23.335: User Data Convergence (UDC); Technical realization and
information flows; Stage 2 for more details
CUPS Architecture

UDC Reference Architecture
©3G4G
• Standardization
of the Data
Model for the Ud
interface
between Front-
Ends and the
UDR is out of the
scope of 3GPP.

Control plane
function group
©3G4G
Data Network
(DN)gNodeB
(NG-RAN)
5G UE
User plane
function
UPF
AMF SMF
NSSF NEF NRF AUSFFE PCFFEUDM AF
UDR
FE
UDC
N1
N2
N3 N6
N4
Nnssf Nnef Nnrf Nudm Nausf Npcf Naf

Application Function (AF)
©3G4G
• The Application Function (AF) fulfils the role of an
application server. It interacts with the 3GPP Core
Network in order to provide services
functionality of AF
CUPS Architecture

Application Function (AF)
©3G4G
Section 6.2.10 of TS 23.501 - The Application Function (AF) interacts with the 3GPP Core Network in order to provide services, for example to support the
following:
• Application influence on traffic routing (see clause 5.6.7),
• Accessing Network Exposure Function (see clause 5.20),
• Interacting with the Policy framework for policy control (see clause 5.14),
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 7.4) 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.

Control plane
function group
©3G4G
Data Network
(DN)gNodeB
(NG-RAN)
5G UE
User plane
function
UPF
AMF SMF
UDR
FE
UDC
N1
N2
N3 N6
N4
Nnssf Nnef Nnrf Nudm Nausf Npcf Naf
AF Application Function
AMF Access and Mobility management Function
AUSF Authentication Server Function
DN Data Network
FE Front End
NEF Network Exposure Function
NRF NF Repository Function
NSSF Network Slice Selection Function
PCF Policy Control Function
(R)AN (Radio) Access Network
SEPP Security Edge Protection Proxy
SMF Session Management Function
UDM Unified Data Management
UDR Unified Data Repository
UDSF Unstructured Data Storage Function
UE User Equipment
UPF User Plane Function

References
©3G4G
• 3GPP: System architecture milestone of 5G Phase 1 is achieved
• 3GPP TS 23.501: System Architecture for the 5G System; Stage 2
• 3GPP TS 23.502: Procedures for the 5G System; Stage 2
• 3GPP TS 23.503: Policy and Charging Control Framework for the 5G System; Stage
2
• 3GPP TS 23.335: User Data Convergence (UDC); Technical realization and
information flows; Stage 2
• 3GPP 5G Core Network Status - TSG CT Chairman, Georg Mayer (Huawei), Nov.
2017
• NTT DOCOMO Technical Journal Vol. 19 No. 3 (Jan. 2018)
• 5G Network Architecture, Design and Optimisation (Jan. 2018) – Andy Sutton

Thank You
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Advanced: 5G Service Based Architecture (SBA)

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