5G NR Architecture Overview

오늘은 5G 네트워크 구조에 대해 살펴보자.

앞서 언급했듯이 LTE와 5G는 공존할 수 밖에 없는 구조 이다.

 

출처 : 삼성전자 White Paer

앞서 언급했다 싶이 LTE 기지국(eNB)와 5G 기지국(gNB)을 Signal과 Data User Plane을 사용하는 방식에 따라

option x로 나뉜다.

option 1,2,5는 SA에 속하고 option 3,4,7은 NSA로 속한다.

 

The 3GPP introduces six architecture options for NR deployment. These architecture options are divided into two deployment scenarios: SA and NSA. The SA provides NR service by using a single RAT, whereas the NSA enables NR deployment by utilizing the existing LTE systems. Options 1, 2 and 5 belong to the SA category, while options 3, 4 and 7 belong to the NSA category. However, since option 1 is a legacy LTE system, in which an E-UTRAN NodeB (eNB) is connected to an Evolved Packet Core (EPC), also referred to as 4G Core Network (CN), it is not considered when dealing with NR deployment scenarios

 

출처 : 삼성전자 White Paer

 

Option 구조에 따라 Core망을 어디로 선택할지 나뉜다.

진화하는 과정에서는 여러 방식으로 선택이 가능하다.

 

In a NSA deployment, Multi-Radio Dual Connectivity (MR-DC) provides a UE with simultaneous connectivity to two different generation RAN nodes (i.e., next generation NodeB (gNB) and eNB). Of the two nodes, one acts as a Master Node (MN) and the other as a Secondary Node (SN). The MN is connected with the SN and 4G/5G CN. The SN can be connected with the Core depending on options.

Generally, MR-DC is categorized. In MR-DC, a UE connects with the MN/CN and can communicate with SN via MN for control plane. For user plane, a UE can connect with either MN/SN directly or SN via MN.

 

 

Option에 따라 자세한 설명을 살펴보자.

Option 2

Option 2 is a NR SA option, in which the gNB is connected to the 5GC. This NR SA option is suitable for greenfield 5G operators. The gNB can communicate with UEs without the help of a legacy network. This option introduces both 5GC and RAN from day one and is the ultimate goal of 5G migration paths. It can fully support new 5G services including enhanced Mobile Broadband (eMBB), massive Machine-Type Communication (mMTC), Ultra- Reliable Low-Latency Communication (URLLC) and network slicing. Since dual connectivity is not a mandatory requirement for this option, it requires less workload when upgrading an eNB for interworking with the NR system. This option will be discussed in more detail in the migration chapter that follows.

 

Option 2는 SA모드이다. 이 방식으로 구성되면 5G의 기본 서비스인 EMBB, eMTC, URLLC를 지원가능하다.

 

Option 3/3a/3x

Option 3 family is a NSA option, in which the en-gNB is deployed in the LTE network and thus does not need a 5GC. In this option 5G services are deployed using the EN-DC with the LTE as MN and the NR as SN. This option may be preferred by operators that already have a nationwide LTE network, because it allows quick 5G migration with minimum LTE upgrade without 5GC. However, it also has a disadvantage, in that, the scope of 5G services is restricted to RAN capability due to its dependency on the legacy EPC. For example, URLLC or network slicing is not supported. Therefore, operators choosing option 3 has a long term task of migrating to option 2, if they are to provide the full extent of 5G services. This option is further divided into three types based on the traffic split method as shown in Figure 3.

Option 3는 NSA의 기본 기술이다. 많은 통신사 들이 LTE가 갖춰진 망에서 5G 기지국만 구축해서 선택하는 방식이다.

 

 

From a control plane perspective, the eNB is connected to the EPC, and the en-gNB operates with the eNB via X2 interface for all option 3 variants. For user plane, traffic split is done at the eNB for option 3, while traffic split in option 3a is done at EPC. In option 3, the eNB can transmit user plane traffic from the EPC toward the UE directly over the LTE air interface or forward a part of the traffic to the en-gNB via X2 interface. In option 3a, the EPC can transmit/receive user traffic to/from both the eNB and the en-gNB. Option 3x is a combination of option 3 and 3a where the EPC can deliver user traffic to either eNB or en-gNB, which forwards them to the UE over the air. The en-gNB can steer the received user plane traffic toward the UE directly over the NR air interface or indirectly through the eNB via X2 interface.

 

Option 4/4a

Option 4 family is a NSA option, in which the gNB is connected to the 5GC, and both gNB and ng-eNB are connected with each other. In this option, the eNB needs to be upgraded to ng-eNB in order to interwork with the 5GC or gNB. This option supports NE-DC to aggregate NR and LTE traffic. The option is further divided into two types depending on the traffic split method used, as shown in Figure 4.

 

 

From a control plane perspective, the gNB is connected to the 5GC, and the gNB operates with the ng-eNB via Xn interface for option 4 and 4a. For user plane, traffic split is done at the gNB in option 4, while it is done at the 5GC in option 4a. In option 4, the gNB can transmit user plane traffic from the 5GC toward the UE directly over the NR air interface or forward indirectly a part of the traffic through the ng-eNB via Xn interface. In option 4a, the 5GC can transmit/receive user traffic to/from both the gNB and ng-eNB.

 

Option 5

Option 5 is a SA option, in which the ng-eNB is connected to the 5GC through the NG interface, but without dual connectivity with NR systems. In this option, the EPC is replaced by the 5GC in the existing LTE network. The eNB needs to be upgraded in order to interwork with the 5GC. The ng-eNB can provide some 5GC-enabling benefits such as network slicing. However, this option isn't highly beneficial since it does not utilize the benefits of 5G NR air interface such as mmWave, multiple numerologies, and flexible frame structure.

 

Option 7/7a/7x

Option 7 family is a NSA option, in which the eNB is connected to the 5GC, and both the eNB and gNB are connected with each other. In this option, the eNB needs to be upgraded to ng-eNB in order to interwork with 5GC or gNB. It supports dual connectivity called NGEN-DC to aggregate NR and LTE traffic. This option is divided into three types based on the traffic split method as shown in Figure 5.

 

From a control plane perspective, the master ng-eNB is connected to the 5GC, and the ng-eNB operates with the gNB via Xn interface for all option 7 variants. For user plane, however, traffic split is done at the ng-eNB in option 7, while it is done at the 5GC in option 7a. In option 7, the ng-eNB can transmit user plane traffic from the 5GC toward the UE directly over the LTE air interface or forward a part of the traffic through the gNB via Xn interface. In option 7a, the 5GC can transmit/receive user traffic to/from both ng-eNB and gNB. Option 7x is a combination of option 7 and 7a where the 5GC can deliver user traffic to either ng-eNB or gNB; then the ng-eNB forwards them to the UE over the LTE air interface. The gNB can transmit the received data from the 5GC toward the UE directly over the NR air interface or forward a part of the traffic through the ng-eNB via Xn interface.