8 networking options for 5G

Some people say that the path to 5G evolution is as complicated as a maze.

Unlike in the past, there are as many as 8 options for 5G networking architecture. Except for Option 1 which is the 4G architecture, Options 6 and 8 have been abandoned by the industry, leaving five options: Option 2, Option 3, Option 4, Option 5 and Option 7. Among them, Options 3, 4 and 7 also include different sub-options.

Our task today is to make these options clear.

Simply put

Simply put, 5G networking includes the following solutions:

• Option 1, independent networking (SA), that is, LTE base stations are connected to the 4G core network, which is the current networking architecture of the 4G network.
• Option 2, standalone networking (SA), that is, the 5G NR base station is connected to the 5G core network.
• Option 3, non-standalone networking (NSA), that is, LTE and 5G NR base stations are dual-connected to the 4G core network.
• Option 4, non-standalone networking (NSA), that is, 5G NR and LTE base stations are dual-connected to the 5G core network.
• Option 5, independent networking (SA), that is, LTE base stations are connected to the 5G core network.
• Option 7, non-standalone networking (NSA), that is, LTE and 5G NR base stations are dual-connected to the 5G core network.

It sounds a bit like a tongue twister, so let me explain it with a picture.

We also have to mention dual connectivity (DC) here.

Dual connection technology was first proposed in the 3GPP R12 version, which is the 4G era. Its basic principle is to allow a mobile phone to connect to two (or more) nodes (base stations) in the wireless access network, one of which is the main node, responsible for the control plane of wireless access, that is, responsible for processing signaling or control messages; and the other (or more) nodes are auxiliary nodes, which are only responsible for the user plane, that is, responsible for carrying data traffic.

Why does R12 introduce dual connection technology? It is mainly to improve network speed, balance network load, avoid switching interruptions, and ensure robust mobility.

Entering the 5G era, the principle of LTE/NR dual connection is basically the same as the LTE/LTE dual connection principle of R12. Either the LTE base station (eNB) is the main node and the 5G base station (gNB) is the auxiliary node; or the 5G base station (gNB) is the main node and the LTE base station (eNB) is the auxiliary node.

After this brief introduction, let's take a closer look at each networking option.

Option 3 Series

The 3GPP Release 15 NSA NR standard completed in December 2017 is based on the Option 3 series.

In the Option 3 series, the terminal connects to 5G NR and 4G LTE simultaneously, the control plane is anchored to 4G, and the 4G core network is used.

On the control plane, Option 3 series completely relies on the existing 4G system. But there are differences in the anchor point of the user plane, which is why Option 3 series has three sub-options: 3, 3a and 3x.

What is the difference between options 3, 3a and 3x?

1. Option 3

The characteristics of option 3 are as follows:

• The control plane and user plane of the 5G base station are both anchored to the 4G base station.
• The 5G base station does not communicate directly with the 4G core network; it is connected to the 4G core network through the 4G base station.
• 4G and 5G data traffic is diverted at the 4G base station before being transmitted to the mobile phone terminal.
• The Xx interface between the 4G base station and the 5G base station must support both the control plane and 5G data traffic, as well as traffic control, and must meet latency requirements.

Obviously, the biggest problem with Option 3 architecture is the overwhelming pressure on 4G base stations.

Since 4G and 5G data traffic are diverted (or aggregated) to 4G base stations, this means that 4G base stations have to process 4G+5G traffic at the same time. The peak rate of 5G is dozens of times that of 4G, and the original 4G base stations are not designed for 5G high-speed rates. Therefore, 4G base stations will inevitably encounter processing capacity bottlenecks.

The solution is to upgrade the hardware of 4G base stations.

However, upgrading 4G base stations costs money, and some operators are bound to be unwilling to do so. Therefore, 3GPP has introduced two more options - Options 3a and 3x.

2. Option 3a

The difference between Option 3a and Option 3 is that 4G base stations are no longer overwhelmed, and 4G and 5G data traffic is no longer diverted and aggregated through 4G base stations. Instead, the user planes are directly connected to the 4G core network, and only the control plane is anchored to the 4G base station.

Although option 3a reduces the burden on 4G base stations and does not require a lot of money to upgrade the hardware of 4G base stations, it has new disadvantages.

First, on the user side, 4G base stations and 5G base stations are directly connected to the 4G core network respectively, and there is no X2 interface interconnection between the two. This means that the two will each carry 4G and 5G independently without load sharing. For example, the 4G base station may only carry VoLTE voice traffic, while the 5G base station may only carry Internet traffic.

At the same time, when the mobile phone "switches" from the 5G base station to the 4G base station, the core network needs to perform S1 (the interface between the base station and the core network) Path Switch, so there is a little "switching" delay.

3. Option 3x

Option 3x can be seen as a combination of option 3 and option a.

Under option 3x, the control plane is still anchored to 4G, but on the user plane, the 5G base station is connected to the 4G core network, and the diversion and aggregation of user data traffic is also completed at the 5G base station, either directly transmitted to the terminal or part of the data is forwarded to the 4G base station through the X2 interface and then transmitted to the terminal.

The Option 3x architecture is future-oriented. It solves the performance bottleneck problem of 4G base stations under the Option 3 architecture, eliminating the need for hardware upgrades of existing 4G base stations. It also solves the problem of 4G and 5G base stations operating separately under the Option 3a architecture.

For some low-speed data streams, such as VoLTE, they can also be transmitted directly from the 4G core network to the 4G base station.

So far, most carriers have chosen option 3x.

Option 2

Option 2 is to independently network 5G base stations and 5G core networks, and "package" the 5G core network and access network together at one time to enter the 5G era.

In non-standalone networking, 5G and 4G interoperate at the access network level, making the interconnection more complex. In option 2, standalone networking, the 5G network is independent of the 4G network, and 5G and 4G interoperate only at the core network level, making the interconnection simple.

▲Under Option 2 architecture, 4G and 5G networks are interconnected at the core network level

But the problem is that unlike the Option 3 series which relies on the mature 4G network and ecological scale advantages, once operators choose to build a network from Option 2, it means that they will need to invest heavily in building an independent 5G network. In the current situation where new 5G use cases have not yet emerged, this requires operators to balance the protection of 4G assets and investment in 5G network construction.

Option 7 Series

The Option 7 series includes three sub-options: 7, 7a and 7x. It is similar to Option 3 and can be seen as an upgraded version of the Option 3 series, except that the Option 3 series connects to the 4G core network, while the Option 7 series connects to the 5G core network, with both NR and LTE migrated to the new 5G core network.

Option 4 Series

Option 4 series includes two sub-options 4 and 4a. Under Option 4 series, 4G base stations and 5G base stations share the 5G core network, with the 5G base station being the master station and the 4G base station being the slave station.

Option 4 requires a fully covered 5G network, so it is preferred by operators who deploy 5G in frequency bands less than 1 GHz.

Option 5

Option 5 connects 4G base stations to the 5G core network, similar to option 7, but without dual connectivity with NR.

Operators who choose option 5 attach great importance to the cloud-native capabilities of the 5G core network. For example, the British operator Three plans to migrate its 4G core network to the 5G core network in advance to help some corporate private networks access its 5G core network early and provide them with flexible network slicing services. It also hopes to provide cloud gaming services to consumers as soon as possible.