5G Network Architecture
In this post, we will learn 5G Network Architecture.
The control plane in 5G network includes the AMF, the SMF, the AUSF, the UDM, and the PCF.
While the user plane includes the UPF.
The control plane is not including those network functions only, there are another network functions in the control plane, that will be discussed later.
In the following diagram, the network functions in Yellow colour, represents the control plane in 5G Network Architecture.
While the Nodes in Green colour represents the user plane.
The only network function from the core network that works in the user plane is the UPF.
First let’s take a look on the AMF
The AMF refers to ‘Access and Mobility Management Function’.
From its name, the main function of the AMF, is to control the access of the UE, to the 5G network. And the make mobility management for the UE.
The AMF, is the first point in the control plane, that connects to the gNB.
From its name, the AMF performs access management and mobility management, for the UEs.
Access management means that, the AMF authenticates the UEs, and authorises the UEs to be able to access the 5G network.
Mobility management means that, the AMF knows the location that the UE currently exists in, and manages the process of UE mobility, while it is moving from one location to another.
Next, let’s take a look on the function of the SMF
The SMF refers to "Session Management Function". The session here means the data session that is used to send or receive user plane data, between the UE and the data network.
From its name, The SMF mainly is responsible for session management. This means it is responsible to establish, modify or terminate the data session.
In addition, the SMF is responsible to select and control the UPF. It selects which UPF should serve each data session. In addition, the SMF is the node in the control plane, that have direct responsibility to control the UPF during the data sessions. This means that the SMF provides its instructions to the UPF continuously during the data session, in order to control its behaviour .
Now, let’s take a look on the AUSF
The AUSF refers to "Authentication Server Function".
Simply, the AUSF is the node that the AMF communicates with, in order to authenticate the UE when needed.
Next, the UDM - 5G Network Architecture
The UDM refers to "Unified Data Management". And it provides user subscription data. (Like the HSS in LTE)
As example, it provides the data that are used to authenticate the UE. So that the AUSF communicates with the UDM during UE authentication.
But the UDM does not have a data base to store the subscription information of the UEs. So there is another node called the UDR.
The UDR refers to "Unified Data Repository". And it is the data base that stores the subscription information of all UEs in the network. So that the UDM communicates with the UDR, in order to be able to deliver the subscription information for the UEs.
Now let’s take a look on the PCF
The PCF refers to "Policy Control Function".
The PCF provides a unified policy framework to control network behaviour.
As example, it provides the QoS rules that should apply to the data session.
The SMF communicates with the PCF in order to get the QoS rules, and then send those QoS rules to the UPF and the gNB, and the UE, in order to apply them to the data session.
The UDR as well stores subscribed policy information for all the users in the network. So the PCF may also access the UDR, in order to get the policy that should be applied to a certain UE.
Finally, the UPF - 5G Network Architecture
The UPF is the only network function from the 5G core network that works in the user plane.
The UPF refers to 'User Plane Function'.
The function of the UPF is that it performs inter-networking between the 5G network, and the data network.
In addition, the UPF applies the session management related parameters received from the SMF to the PDU session of the UE.
5G Network Architecture - Summary
The control plane in 5G Network Architecture contains the AMF which is the first node in the control plane that connects to the gNB. And it is responsible for the access and mobility management.
The SMF, that is responsible for session management.
And the AUSF that is responsible to authenticate the UEs along with the AMF and the UDM.
In addition to the UDM that provides subscription data of the UEs.
And the PCF that is responsible to provide a unified policy framework to control network behaviour.
While the user plane includes the UPF, which performs inter-networking between the 5G network, and the data network. And the UPF applies the session management related parameters received from the SMF to the PDU session of the UE.
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