What is the architecture of the 5G network? We will try to answer that question in this video. Let's start with the basic principles. 5GC networks are based on IP networks. They can be used to carry any data, PDUs, such as Ethernet frames or IP packets, but the core network is always based on IP technology. Dataflow management remains the same as for 4G. That is to say that we use the same tunneling idea, which means that a PDU is encapsulated in another IP packet and the GTP-U protocol is used. GTP-U refers to GPRS Tunneling Protocol in the user plane. 5G network architecture can be described by basing our understanding on 4G network architecture. There are base stations called gNBs. The base stations forwards the packets, the dataflow to the user plane function or UPF. There can be more than one UPF. The UPF can be considered the equivalent of parts of the Serving Gateway and the Packet Gateway. The UPF must first interconnect with the data network at a given location even if the UE moves. This is known as mobility anchoring. The UPF is also involved in packet forwarding for data PDUs when tunneling is enforced. In other words, it removes or adds tunnel-related headers, that is to say, the GTP-U headers. Finally, there are some more specific functions, such as the possibility of inspecting packets. For example, to identify or detect a particular application within the flow according to a flow templates with certain values in the fields as indicated by the equipment controlling the UPF. It is also possible to apply a policy for quality of service to give some packets priority over others. This policy is enforced by the UPF. The MME is here replaced by two entities, AMF or access and mobility management function and SMF. The AMF enables NAS dialogues between the UE and the AMF to manage access and mobility. Of course, the messages do physically pass through the gNB, but there are not processed there. We have the equivalent of a direct dialogue, which is still the principle of NAS. The SMF is used to control the UPF. SMF stands for session management function. More specifically, the AMF can exchange signaling with the terminal for registration purposes, as well as managing mobility, the mobility of the UE, connection management, and UE reachability. This means that it can send paging messages to the UE on multiple cells. Just like 4G, messages exchanged by the UE and the AMF are encrypted and integrity management is assured for the NAS signaling messages. The AMF is responsible for access, authentication, and managing access authorizations and can be used as a relay by other services, such as geolocation services, where geolocation messages can pass through the AMF. Finally, it has notification functions for UE mobility related events, which can then be relayed to third party service provider. The SMF controls the UPF. It can exchange signaling messages with the UE when a PDU session is required. Of course, the signaling messages pass through the AMF and the gNB. The SMF manages the session, the setup, the modification, and the release of PDU sessions by controlling the UPF. It also manages addresses. Namely, the SMF allocates IP addresses to UEs. Another distinction between 4G and 5G is that the HSS is replaced by AUSF and UDM in 5G. AUSF means authentication server function. It manages authentication of the UE and also keying material. UDM, or unified data management function, instead manages user and subscription identifications. To clarify, we can imagine that the UDM is a bit like a front-end providing access to all the data relating to UE subscription. It's possible to manage subscription as well as handling authentication information. User's identity are also managed, which means that it is the UDM which stores and manages the SUPI. There are also access authorizations relative to subscription data, such as potential roaming restriction. Finally, the UDM memorizes the AMF that manages each UE as well as the SMF or SMFs when there are multiple PDU sessions for UE. It will also known the SMS gateway managing the UE. In conclusion, in a 5G network, dataflow is managed using GTP-U, which is very similar to what is done in 4G. The MME becomes AMF plus SMF. SMF to control the UPF, AMF to communicate with the terminal. Finally, HSS is replaced by two functions, namely UDM for managing subscribers and subscriber profiles, and AUSF for managing security keys.
