Apis TechTip – The 5G System Architecture

Welcome to the second episode of Apis TechTips, a video series of excerpts from courses available at Apis training. 

This episode gives you a high-level view of the 5G System Architecture and comes from the course 5G Core Network in an Hour. 

Did this Apis TechTip boost your taste for knowledge? Learn more in our full course 5G Core Network in an Hour. The course offers a condensed view of the 5G Core Network as specified by 3GPP, while also summarizing important improvements and new concepts when comparing with 4G. 

The course covers the following topics: 

  • Rationale behind defining a new system: why not LTE?
  • 5G Deployment Options
  • Service Based Architecture, SBA
  • 5G Core Network Features
  • Resource Definitions for 5G
  • Service Influencing

Learn more about 5G Core Networks here: https://apistraining.com/portfolio/5g-core-network-in-an-hour/

This TechTip is also part of a whole eBook of tips, all focusing on 5G technology. We call it an eBook+ since all chapters are both text and video. If you want to read the text, you can do that, and if you want to watch a teacher tell the story, you can choose that.

All the video chapters are excerpts taken directly from our recorded lessons, so if one of them piques your interest, you can easily go to the course and dive deeper into that particular subject.

This particular eBook+ is called “5G Demystified: Use Cases, Architecture, and More”, and you only need to CLICK HERE to request it for immediate download.

Below you can find the transcribed text for this particular TechTip.

The 5G System Architecture

In the image, I would like to show you the general definitions of the architecture, which is based on the bold horizontal line in the middle. This is called the service-based architecture representation.

This horizontal line is a communication line that interconnects the elements in the 5G network. These elements in the 5G core network are different network functions. Each network function is defined in the standards, and it has defined capabilities of what it is and what it does. So, for example, the AMF, which is the access and mobility management function, is responsible for a User Equipment’s (UE) access and for managing its mobility.

Now, in order to manage the UE, the AMF network function offers certain services. These services are opened to anybody who is on the horizontal communication bus, using a service-based interface. The interface is called capital N and then the name of a network function that offers these services. So, the AMF is reached by the Namf interface.

And in the 5G core network, you can see that there is a large number of these atomic capabilities defined. In the standard, they try to see what needs we will have in order to handle different subscribers with the different applications we are using. And then, we define a number of functionalities to help us with a different aspect of treating the subscriber.

In the image, you can see, for instance, the Session Management Function (SMF) to manage sessions, the Policy Control Function (PCF) to manage policies, the Authentication Server Function (AUSF) to manage authentication, and so on. These are, as I say, atomic capabilities for some quite detailed handling of a particular user equipment. You can see a UE over on the left. It can contact the core network, but of all the network functions I mentioned, the UE speaks only to the one called AMF, Access and Mobility Management function.

The N1 line is a logical interface that interconnects the UE and the AMF. In reality, the actual bits, the real communication, go over the access network, and then the access network acts as a relay towards the AMF. So the access network called NG-RAN, or Next-Generation Radio-Access Network, is where the information goes through physically.

We are talking about the core network, which is the whole upper part of the picture, but we get connectivity over the access network, NG-RAN. And in the NG-RAN cloud, you can see the New Radio (NR), which is the specialized 5G radio technology. There is also the possibility of having non-3GPP access; that’s why it says Wi-Fi on the line towards the UE.

3GPP, or the Third Generation Partnership Project, is a standardization group that does almost all of the standardization work for the 5G system, and they are the source of all the pictures and information that I’m showing you. So when it says non-3GPP, it simply means we are talking about something that was not defined in the documents prepared by this particular group of people.

So I can have a user equipment speak to the core network, indicating what it is that it would like to do. Ultimately, what we would like to do is we would like to be able to send data from the application client that sits on this user equipment to the application server that is somewhere out in the data network on the other end of the picture, over on the right. This means I need to interconnect. I need to create a, as we call it, user plane connection going from the UE over some radio resources to the access network, then continuing into a network element called the User Plane Function (UPF). The UPF is like an IP router, and through potentially a sequence of these user plane functions, we end up having the user data go out of the 5G operator’s environment and enter the data network where we have the application servers.

In this picture, I’m talking basically about a user equipment that is using its own operator’s network, meaning the UE is a paying subscriber on this particular network. But you can have communication between your operator and some other operator as well. The ”Other PLMN” (Public Land Mobile Network) cloud on the right side of the picture is another mobile operator. And you can see that the interconnection between operators goes through an element which is called Security Edge Protection Proxy (SEPP). Security is a big thing in the 5G specification, and this SEPP is an inter-operator security thing.

One more thing I would like to point out: communication with some external data network, either locally or going through the SEPP to some other place, is about getting access to the application information from an external application function. Please note that there is a possibility of communicating from the customer of the mobile operators into the mobile operator’s network. The external application function in the top right seems to have the possibility to talk to the elements on the 5G operator’s communication bus. This happens through an element which is called the NEF, Network Exposure Function, which is responsible for securely exposing the capabilities of a mobile operator’s network to some external influence. This basically means that the customer of a mobile network can indicate to the operator of the network how it wants the user plane to look.

This way, we can much better work with the concept that a one-size-fits-all network is no longer the correct approach. In the 5G system, you can have much more precisely structured, logical networks that are going to carry data from certain applications with certain needs. These needs are usually represented by one of the five main 5G use cases.

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