In this chapter we shall see 5G Service Based Architecture.
The 5G SBA showed below is taken from the Technical Specification TS 23.501.
In 4G we used to call the functions as network elements. In 5G we call them as Network Functions.
As you can see in the above image, there are 2 entities.
1. User Plane entities.
2. Service Based Architecture entities.
Now if you can see, the user plane entities are connected together with point to point links or they can be called as Reference points. Reference point architecture is what we saw in previous chapter.
SBA entities are connected together with Service Based Interface. They use HTTP/2 over TCP. They can also use REST-style API and JSON.
The User Plane entities and SBA entities are called as Network Functions. In the next chapter we shall see the functionality of all the Network Functions.
what are the different ways that Network Functions can communicate with each other?
In 5G Core Network, we saw that they are connected using SBA Interface.
5G SBI (Service Based Interface) uses below protocols.
1. REST: Representational State Transfer
* REST is API based
* Stateless
* Client – Server based architecture.
2. HTTP 2.0 over TCP
* Uses GET, POST methods
* header compression
* widely accepted and deployed
3. QUIC: Quick UDP Internet Connections
* Replacement of TCP/TLS connections
* Currently in development by IEFT
4. JSON
The network stack will be as below:
What is the use of Service Based Interface over point to point links?
This is a new feature that has been designed in 5G Core. Instead of using interfaces, they have decided to use API’s to interact between the SBA entities.
They have many advantages like:
* As we are moving to cloud, point to point will not work.
* As 5G architecture is designed to be Cloud Native (CN), a cloud native architecture should make use of network functions virtualization (NFV) and Software Defined Networking. SBA interface will help to achieve this.
* It will help to achieve modular design.
* Can be easily scalable.
* The services can be run independently and can manage independently without affecting each other.
* It will enable virtualization and slicing.
* 3rd parties applications can be integrated with 5G network.
Reference points
In the above image we can see the below mentioned reference points;
N1: Reference point between the UE and the AMF.
N2: Reference point between the (R)AN and the AMF.
N3: Reference point between the (R)AN and the UPF.
N4: Reference point between the SMF and the UPF.
N6: Reference point between the UPF and a Data Network.
N9: Reference point between two UPFs.
Service-based interfaces
In the above image we can see the below mentioned Service based interfaces;
Namf: Service-based interface exhibited by AMF.
Nsmf: Service-based interface exhibited by SMF.
Nnef: Service-based interface exhibited by NEF.
Npcf: Service-based interface exhibited by PCF.
Nudm: Service-based interface exhibited by UDM.
Naf: Service-based interface exhibited by AF.
Nnrf: Service-based interface exhibited by NRF.
Nnssf: Service-based interface exhibited by NSSF.
Nausf: Service-based interface exhibited by AUSF.
Nudr: Service-based interface exhibited by UDR.
Nudsf: Service-based interface exhibited by UDSF.
N5g-eir: Service-based interface exhibited by 5G-EIR.
Nnwdaf:Service-based interface exhibited by NWDAF.
It means the communication between the different SBA network functions will take place based on REST API or JSON or HTTP 2.0 over TCP.
Below image shows the mapping of network functions