Is the management of sporadic flows the same in 5G and 4G? This is what we will see in this video. In this diagram, we have represented the state of tunnels and connections in 4G, when data is exchanged. We focus particularly on connections close to the terminal, I mean, in the access network. We have the radio connection between the UE and the eNodeB, but also the data tunnel between the eNodeB and the Serving Gateway N and S1-AP connection between the eNodeB and the MME. When data is exchanged, there is a radio context stored by the eNodeB. Because the radio connection is established, the terminal is said to be in RRC-connected state. The radio context corresponds, for example, to the radio characteristics of the terminal. Seen from the core network and thus from the MME, the terminal is in ECM-connected state. If there is no radio activity, the terminal is in ECM-Idle state, meaning there is no S1-AP connection between the eNodeB and the MME. There are no longer data tunnels between the eNodeB and the Serving Gateway. There is also no longer any radio connection, I mean, there are no context related to this UE in any eNodeB. How do we transition from one state to another? We see it here, in this scenario, we have illustrated the time that passes and the fact that the terminal exchanges data with the network. Data exchanges occur. After a while, the exchange stops and the eNodeB starts a timeout. If data is exchanged again, before this timeout expires, the terminal remains in RRC-connected, ECM-connected state. If the timeout expires, the terminal will be switched from the connected state to the RRC-Idle, ECM-Idle state. When the radio connection tunnels and connections between the eNodeB, the Serving Gateway and the MME are released, there are signaling exchange. This generates a load on the MME, which will have to process messages, and the same goes for the Serving Gateway. After a while, if data is exchanged again, there will be the transition to the connected state and therefore signaling exchanges and thus some load. Let's take a look at the evolution of mobile services over the last 30 years. In the nineties, we used our terminal only to make phone calls. We can consider that we made one call per hour during peak periods, so there were little access. With the development of new services, in particular, short messages, SMS, the number of accesses on the network increased a bit. We estimate that each user access the network few time per hours, on average, between 2000 and 2005. With the deployment of mobile applications on the terminal, much more access to the network occurred. We can estimate that we will have up to ten or several dozen access requests per hour. This means that every time we have radio activity, we have to establish the connection. If we are in 4G, the terminal has to be put in ECM-connected state. Every time we release the connection signaling occurs: signaling to the MME. That signaling loads the network and leads to significant access delays. In 5G, we'll keep the general philosophy of 4G but with some evolution. We find a state called CM-connected state associated with an RRC-connected state. In this state, there's a radio connection between the UE and the gNB. A data tunnel between the gNB and the UPF, and a connection between the gNB and the AMF. Note that in this state, it is the network that chooses the gNB the UE is connected to. We also have the CM-IDLE state where we no longer have a radio connection between the UE and the gNB, tunnel between the gNB and the UPF, or a connection between the gNB and AMF. In this state, RRC-idle/ CN-idle mobility is controlled by the UE. In other words, the UE chooses which gNB it listens to. What's new in 5G is the introduction of a new state called RRC-inactive. In this state, we release the radio connection between the UE and the gNB, but we keep the older tunnels and connections. In particular, we keep the data tunnel between the gNB and the UPF, as well as the connection between the gNB and the AMF. This allows us to hide the transition from the RRC-connected state to the RRC-inactive state for the AMF. The AMF and the entire core network still see the terminal as being in CM-connected state. This makes it much easier to restore connectivity since we only need to restore the radio connection. Since all the tunnels are maintained, there are nothing to do in the access network. In this RRC-inactive state, mobility is controlled by the UE. The UE itself, chooses which gNB it listens to. To summarize, in 5G, there are 3 RRC states for UE. First RRC-connected, which corresponds to CM-connected in the AMF. All tunnels and connections are established. Second, RRC-idle, which corresponds to the CM-idle state. There are no connection or channel in the access part. Third, there is a new state called RRC-inactive, which corresponds to the CM-connected state, but without a radio connection. However, the connections and tunnels between the gNB and the UPF and between the gNB and the AMF are maintained. In the RRC-inactive state, mobility is controlled by the UE, as in the RRC-idle state. The general strategy is that in case of short inactivity, we will switch from RRC-connected to RRC-inactive. If the inactivity is a bit longer, we will go back to RRC-idle state to free all the tunnels and connections on the access network. The main advantage of the RRC-inactive state is that end-to-end connectivity is easier and quicker to restore, since we only have to restore the radio connection. The second advantage is that there will be less signaling load on the AMF, SMF, and UPF. This is true in general. It depends on the behavior of the terminal. There may be special cases where this is not true, but in general, there is less signaling load.
