5G SBA (Service-based Architecture)

Basic Principles 

• A control plane NF can provide one or more NF services. 
• An NF service consists of operations based on either a request-response model.
• Common control protocol using HTTP-based API, replacing protocols like e.g Diameter.

Building blocks 

• Network and Resource Management
• Signaling
• Subscriber data 
• Application function and Network Exposure Function
• Location services
• Subscriber management
• Policy
• Control plane 
• User plane 
• Access network

Functions in the core network

AMF

5G core Access and Mobility Management Function receives all the control and session-related information from the user equipment. It is responsible for the handling of connection and mobility-related tasks. It is connected to the SMF with the N11 interface. A mobile network comprises many AMF instances and each AMF is uniquely identified by GUAMI (Globally unique AMF identifier). It implements NAS (Non-Access Stratum) Ciphering and integrity protection algorithms. It is responsible for Lawful intercept, Access Authentication, and Authorization. It also performs Security context management.

SMF

It is the fundamental element of the 5G core network architecture which is responsible for interacting with decoupled data plane, creating, updating, and removing PDU (Protocol data units). It manages the session context with the User plane function. The functions performed by SMF include UE IP address allocation and management, termination of interfaces, downlink data notifications, charging data collection, lawful intercept, roaming functionality, etc.

UPF

It is the fundamental component of a 3GPP 5G Core Architecture. It represents the data plane evolution of a control and user plane separation (CUPS). The functions of UPF include QoS handling for the user plane, packet routing, and forwarding, packet inspection, lawful intercept for the user plane, traffic accounting and reporting, etc. 

AUSF

It is an Authentication Server Function that performs the authentication of the user equipment. It is located in a home network. It makes the decision on UE Authentication for authenticating data and keying material like 5G AKA and EAP-AKA used. It is used to facilitate 5G security purposes.  

NSSF

 It is used by AMF for the selection of Network Slice Instances that will serve a particular device. It selects the Network Slice Instances determining the allowed network slice selection Assistance information (NSSAI). It can retrieve NRF, NSI ID, and target AMFs as a part of the UE registration process and PDU establishment process. 

NEF

Network Exposure function facilitates secure, robust, developer-friendly access to network services. This function provides a means to securely expose the services and capabilities which are provided by 3GPP network functions. 

NRF

The network Repository function works as a central repository for all the 5G network functions in the operator’s network. NRF allows 5G NF’s to register and discover each other with the help of standard APIs. It maintains the profiles of the available NF instances and their supported services in the 5G core network. Allows NF instances to track the status of other NF instances. 

PCF

It supports the unified policy framework that governs the network behavior. It provides policy rules to enforce them. To facilitate this, the subscription information is gathered from the Unified data management function. It provides policy rules for control plane functions, which include network slicing, roaming, and mobility management. 

UDM

It is a centralized way to control network usage data. It is cloud-native and designed for 5G technology. The functions of UDM are similar to HSS (Home Subscriber Service). It generates 5G AKA Authentication vectors, user identification handling,  this function stores the long-term security credentials used in Authentication for AKA. It stores subscription information.

AF

It requests dynamic policies and/or charging control. It performs operations like accessing the Network Exposure Function for retrieval of various resources. It interacts with PCF for policy control, application traffic routing, exposing services to end-users, etc.AF exposes the Application layer for interacting with 5G network resources. 

DN

DN is a data network that is related to the 3GPP 5G Architecture. It could be operator services, internet access, or other services. 

Benefits of moving to 5G SBA 

Network functions are loosely coupled and interfaced with APIs, each NF can be evolved and deployed independently. It brings scalability, rather than adding physical nodes that may take time, with this new instances of NFs can be created/destroyed dynamically in minutes. If an instance or a physical node fails, monitoring systems can detect this and spin multiple instances. SBA’s design enables network slicing. Multiple logical networks can run on a single physical network. Network functions in SBA are exposed via well-defined Service based Interfaces. New NFs can be rolled out without impacting existing ones. It is deployed as containers orchestrated by Kubernetes, allowing the core to run on infrastructure, let’s, new software vendors plug-and-play their NFs for the best of breed approach, it enables network slicing with dynamic and efficient resource utilization, it simplifies operations using Application programming interfaces (APIs), it facilitates seamless integration of third-party vendors applications with the core network. 

The 5G Core network builds on control and user plane separation introduced in 3GPP. It specifies NFs that support multiple applications that can be joined as Network Slices. A 5G Stand  Alone network will leverage the full potential of SBA which could elevate the mobile network experience.