5G NSA and SA Network Modes
5G NR Network Mode Options Defined by 3GPP
For 5G network architecture, 8 options were proposed at the 72nd general meeting of 3GPP TSG-RAN, as shown in the figure below.
8 options for 5G network architecture
These 8 options are divided into two groups: SA modes (Standalone) and NSA modes (Non-Standalone). Options 1, 2, 5, and 6 are SA modes, while options 3, 4, 7, and 8 are NSA modes. And options 3, 4, and 7 have different sub-options.
Among these options, Option 1 has already been implemented in the 4G structure, while Option 6 and 8 are only theoretical deployment scenarios without practical deployment value, and will not be considered in the standard.
Let's discuss them one by one, starting with SA modes.
SA Option 1
Option 1
The figure above shows the architecture of Option 1, which is a pure 4G networking architecture.
Notice that there are a solid line and a dashed line between the phone, 4G base station and 4G core network. The dashed line represents the control plane and the solid line represents the user plane.
Control plane: the channel to send the signaling required to manage and schedule resources.
User plane: the channel to send the user data. The user plane and the control plane are completely separate.
Option 1 has nothing to do with 5G.
SA Option 2
Option 2
The figure above shows Option 2. The architecture is very simple, that is, 5G base station is connected to 5G core network, which is the ultimate form of 5G network architecture and can support all services of 5G.
Although the architecture is simple, to build such a 5G network, a large number of new base stations and core network should be built, which is very costly.
SA Option 5
Option 5
The figure above shows Option 5. As you can see, this is actually an upgraded 4G base station connected to the 5G core network, which is essentially 4G. However, after the new 5G core network is built, the original 4G core network should be gradually phased out. So, 4G base station is bound to be needed to connect the 5G core network, and thus it is also an architecture that will appear.
However, compared with 5G base stations, the improved 4G base stations still have obvious differences in terms of peak rate, delay and capacity. As for subsequent optimization and evolution, enhanced 4G base station may not be able to support. So, the prospect for Option 5 architecture is not good either.
SA Option 6
Option 6
The Option 6 is to connect 5G base stations to the 4G core network. This option can hardly make use of the power of 5G base stations. Considering that 5G base stations are already a bigger part of investment compared to 5G core network, it’s not really a reasonable choice to trade large investment with little return. Therefore, no carrier will choose this architecture, and 3GPP does not consider standardization of it.
Summary of SA modes
To sum up, there are only Option 2 and 5 for SA modes of 5G, of which option 2 is the ultimate architecture of 5G network.
The advantages of SA Option 2 are as follows:
1. Introduction of 5G base station and 5G core network in one step; independent of the existing 4G network; with the shortest evolution path to ultimate 5G network.
2. Brand new 5G base station and 5G core network can support all new functions and services introduced by 5G network.
Meanwhile, the disadvantages of SA Option 2 are as follows:
1. 5G network has relatively higher frequency than LTE, so it is difficult to achieve continuous coverage during the initial deployment, and thus there will be a lot of switching between 5G and 4G networks, which will result in poor user experience.
2. The initial deployment cost is relatively high and the existing 4G base station resources cannot be effectively utilized.
5G NSA Network Modes
Now let’s talk about NSA network modes. In general, NSA networking architecture is much more complicated than SA networking, which is the price you have to pay to save money.
First, we explain a few terms related:
1. Dual connection: As the name suggests, the mobile phone can communicate with both 4G and 5G networks and download data at the same time. Typically, there will be a master connection and a slave connection.
2. Control plane anchor: the base station responsible for the control plane in the dual connection is called control plane anchor.
3. Data split anchor: the user's data needs to be split for transmission in the two paths of dual connection, but where should it be split? This location is called data split anchor.
The various options for 5G NSA networking are decided with the combinations of answers to the three questions followed.
- The base stations are connected to 4G core or 5G core?
- The control signaling is transmitted by 4G base station or 5G base station?
- The data split anchor is at the 4G base station, 5G base station, or core network?
Options 3, 7 and 4 are different answers to the three questions. Let's introduce them one by one.
Option 3
The Option 3 series is divided into 3, 3a and 3x. The difference lies in data split anchor.
The base station of Option 3 series is connected to 4G core network, and the anchor points of the control plane are all in 4G core. It is suitable for the initial phase of 5G deployment, when the coverage is not continuous, and there is not much 5G service. It exists purely as a supplement to 4G wireless broadband.
Option 3
As shown in the figure above, the data split anchor of Option 3 is on the 4G base station. That is to say, 4G is not only responsible for the control and management, but also responsible for splitting the data from the core network into two paths: one is sent to mobile phones by itself, and the other is distributed to 5G base stations to send to mobile phones.
In order for the 4G base station to handle the heavy tasks, software upgrade is required but still it might be too big a challenge to handle all the 5G traffic.
As a result, Option 3 has been rather unpopular and has not received much attention since it was proposed.
NSA Option 3a
Option 3a
Option 3a makes some improvements by placing the data split anchor on the 4G core network, which distributes user data to the 4G and 5G base stations. While this is much better than option 3, it would require a major upgrade to the 4G core network.
NSA Option 3x
Option 3x
Option 3x cleverly places the data split anchor on the 5G base station. In this way, Option 3x avoids making too many changes to the 4G base stations and 4G core network already in operation, and takes advantage of the fast speed and strong capability of 5G base stations. Therefore, option 3x has been widely adopted by the industry and has become the first choice for 5G NSA networking deployment.
In summary, the advantages, disadvantages and applicable scenarios of Option 3 series are as follows:
Advantages of NSA Option 3:
1. It has the earliest completion time of standardization.
2. There is no requirement for 5G coverage, and dual connection is supported for streaming, providing good user experience.
3. Small network changes, fast network construction, relatively smaller investment.
Disadvantages of NSA Option 3:
1, 5G base stations and the existing 4G base stations must work together, so they need to come from the same manufacturer, which brings low flexibility.
2. Unable to support new functions and services introduced by the 5G core network.
Applicable scenario of NSA Option 3:
To rapidly provide commercial 5G service for high-value zones. Option 3x is recommended.
Option 7
Option 7 Series is a step closer to 5G than the Option 3 Series. In this series, the core network has been switched to the 5G core. In order to connect with the 5G core network, the 4G base station has also been upgraded to an enhanced 4G base station.
However, the control plane anchor of Option 7 series is still on 4G, which is suitable for the early and middle stages of 5G deployment. The coverage is not continuous yet. However, since the core network of 5G has been deployed, in addition to the most basic mobile broadband, the other two services, mMTC and uRLLC, can also be supported.
For this option, the 5G service capability is greatly enhanced, but the coverage needs to be supplemented by 4G.
The Option 7 series is also divided into 7, 7a and 7x, which are differentiated by where data split anchor is located.
Option 7
Option 7a
Option 7x
The data split anchor of Option 7 is in the enhanced 4G base station, Option 7a is in the 5G core network, and Option 7x is in the 5G base station.
Similar to Option 3 series, both Option 7a and 7x are acceptable, but Option 7x is more popular.
In summary, the advantages, disadvantages and applicable scenarios of Option 7 series are as follows:
Advantages of NSA Option 7:
1. There is no requirement for 5G coverage, so we can take advantage of 4G coverage.
2. Dual connection is supported to improve network speed and provide good user experience.
3. 5G core network is introduced to support new 5G functions and services.
Disadvantages of NSA Option 7:
1. Heavy workload is required to upgrade 4G base stations.
2. The industry might be relatively late to become mature.
3. 5G base stations and enhanced 4G base stations must work together, so they need to come from the same manufacturer, which brings low flexibility.
Applicable scenario of NSA Option 7:
In the early and mid-phase of 5G deployment, continuous coverage is provided by enhanced 4G base stations, and 5G is used for high-value zones to improve capacity. Option 7x is recommended.
Option 4 series
Now let's introduce Option 4.
For this series, 5G is completely in the spotlight. The core network has already been switched to the 5G core, and the 5G base station has also become the anchor point of the control plane.
Option 4
Option 4a
Option 4 Series is divided into Option 4 and 4a. As can be seen from the two figures above, the only difference between them is whether the data split anchor is in the 5G base station or the 5G core network. Both of these are new network elements and do not involve the upgrading and transformation of legacy equipment, so both options are acceptable.
The application scenario for Option 4 series is in the middle and late stages of 5G deployment. 5G has achieved continuous coverage, completely leaving 4G behind as a complement to 5G.
Option 8
Switching the 5G core network in Option 4 to a 4G core network, you will get Option 8.
But it’s not reasonable to put the powerful 5G base station as a control plane anchor under the 4G core network, so 3GPP hasn’t considered standardizing this option.
5G networking evolution paths
After talking about the characteristics, advantages and disadvantages of SA and NSA networking modes of 5G, the question arises: how to evolve among so many architectures?
There are two paths of evolution.
Path 1: Go straight to Option 2, which is the ultimate architecture. This requires heavy investment from the beginning.
Path 2: Option 1 → Option 3x → Option 7x → Option 4 → Option 2, all steps in between are optional.
Path 2 looks complicated, and the total cost of multiple investments is greater than the amount of one-time investment. However, the risk is smaller. Gradual investment could be a wise choice.
Two evolution paths of 5G networking architecture
The switch from a 4G core to a 5G core is a big reason why Path 2 looks so complicated. Fortunately, with the gradual maturity of virtualization and cloud computing, the 4G core network and the 5G core network can be combined into a 4/5G fusion core network. In this way, the evolution of wireless network has become much easier, and a variety of network architectures can coexist harmoniously.
In fact, there is only one factor that will determine all of this, and that is the explosion of demand for 5G.
