The objective of this white paper is to provide insights on the 5G deployment option and to present the preferred architecture in Non-Standalone and Standalone network. The target audience of this white paper are service providers and operators who aspire in providing state-of-the-art services to their customers by migrating from existing 4G LTE to the new 5G System. This white paper will facilitate the service providers and operators to choose a preferred deployment or migration option, from an array of “reference deployments”.
1. Introduction
Over the last decade, mobile communication has seen substantial growth. Each, so called, generation of Telecom Networks brought, significant betterment over its predecessor along with newer challenges. 4G augmented solutions that catered services which required higher speeds and lower latency.But sooner or later this will become a bottleneck as the network congestion due to Subscriber growth is evident. That should ultimately lead to one more, so called, generation in the usual growth cycle of Telecom Networks. But this time technologists not only were thinking about Download speed, but a differentiator, that will change the shape of the World. 5G, talks about services like Virtual Reality (VR), Augmented Reality (AR), Vehicle to Everything (V2x), Internet of Things (IoT which evidently required even lesser latencies and faster data speeds.
To address the challenges encountered in 4G and provide 5G services to the subscribers, Operators must deploy an independent 5G network or upgrade existing 4G nodes in a phased manner. In the following sections we will present some feasible options for seamless migration from 4G to 5G.
2. 5G Reference Migration options
As the final goal of operators is to provide 5G services to all the customers, the eventual target path will be Option-2. In the below section different options and migration paths for the operators have been highlighted and represented symbolically.
Figure – 1
| Options | Acronym | Description |
|---|---|---|
|
4G EPC SA |
Existing 4G LTE deployed in Standalone with Evolved Packet Core |
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NR 5G SA |
5G New Radio deployed in Standalone with 5G Core |
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LTE+NR with EPC-NSA |
eNB and NR deployed with EPC and LTE eNB deployed as Primary |
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NR+LTE with 5GC |
NR and eNB deployed with 5GC and NR deployed as Primary |
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LTE with 5GC |
eNB deployed with 5G Core as Standalone |
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NR with EPC |
NR deployed with EPC as standalone |
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LTE+NR with 5GC |
eNB and NR deployed with 5GC and LTE eNB deployed as Primary |
Table – 1
| Deployment migration path for operators | Description | Benefits | Overhead |
|---|---|---|---|
|
Path1 |
Deployment Option2Operators who want to deploy 5GS independently can consider this option Example: Operator may want to deploy 5Gs in specific geographic area for testing purposes. |
Subscribers are fully benefited with all the 5G services |
‘4G only’ subscribers cannot be served. |
|
Path2 |
Migrate from Option-1 → Option-2 Operators who want to migrate from existing 4G LTE to 5GS fully may opt for this option. |
Both 4G and 5G subscribers are served Independently.
5G subscribers will get full coverage and mobility with 4G EPC.
|
Maintenance of two generations of networks Operations costs involved in upgrading existing 4G eNBs to support NR connectivity |
|
Path3 |
Option-1 → Option-3 Operators who want to quickly roll out 5G services by deploying 5G NR with existing Option-1. |
Quick roll out of 5G services |
Core benefits cannot be leveraged by the 5G subscribers |
|
Path4 |
Option-1 → Option-3 → Option-7 → Option-2
|
With Target path (Option2) subscribers can reap 5G benefits With intermediate path (Option7) 5G subscribers can get full 5G core and Ne benefits, while 4G subscribers can reap 4G core benefits Option-3 - refer Path3 |
Since, 5G core is not fully ready yet, time to market will be slower With intermediate options overhead of upgrading eNB and EPC may add to additional operations costs |
|
Path5 |
Option-1 → Option-3 → Option-7 → Option-4 → Option-2 Operators who have long term goal of deploying NR as primary for handling Control Plane traffic. |
With Target path (Option2) subscribers can reap 5G benefits With intermediate path4, 4G subscribers can get 5G core benefits Intermediate option3 and option 7, refer path4 |
Time to market is slower |
Table – 2
2.1. Option-1
This is not a deployment option by itself, but an existing operator deployment worldwide. To provide 5G services, operators must choose any of the following options below.
Figure-2 : 4G Standalone deployment
2.2. Option-2
In this option 5G is introduced in SA mode with 5G gNB and 5G core. In this option, the operator may want to introduce 5G only in specific geographic areas, while they still continue to provide LTE services to the existing users in other geographical areas. This can be an ideal choice for Green Field Operators who want to roll out 5G services. This option can be looked upon as the target migration option for operators.
When operators with existing LTE network deploy 5GS (5G Core + NR) independently, they will have to choose to support interworking with EPC and eNB to provide full coverage and mobility to the 5G subscribers. Existing LTE subscribers without 5G, can be served independently by EPC.
With 5GS deployment, operator can deliver all the 5G services to the 5G subscribers, like, eMBB, URLCC and MMTC in all sectors along with leveraging the benefits of Network slicing, NFV and SDN.
Figure-3 : 5G Standalone deployment
2.2.1. Aspects related to Interworking
To support mobility between 5G users in 4G EPC network, interworking between 5GC and EPC must be supported. The interworking aspects can be further subdivided into,
- RAN level Interworking
- Core Level Interworking
2.2.1.1. RAN Level Interworking
RAN level interworking can be achieved on the Xn interface connecting the LTE eNB and 5G gNB. The eNBs must be upgraded to support the 5NR interface to communicate with gNB and 5GC. In the Interworking scenario, Radio Access can communicate with either EPC or 5GC.
Figure-4 : RAN Interworking connected to EPC
Figure-5 : RAN Interworking connected to 5GC
2.2.1.2. Core Level Interworking
In the Core level Interworking, the LTE eNB does not interact with 5G gNB, but the EPC interacts with the 5GC. The UE connects to either NR or LTE eNB independently. When the subscribers are in 5G area, they can leverage the benefits of 5G core. When they move to an area where there is no 5G signal, they can release the radio bearer connected to 5G NR and establish a new bearer towards eNB. CN may retain the IP address allocated to the user during this mobility. There are two ways in which the interworking may be achieved –
2.2.1.2.1. Single registration mode
In the Single Registration mode, the UE is either connected to 5G NR or 4G LTE at any point in time. During mobility MME from EPC will provide the session context to the AMF in 5GC.
To support the MME–AMF & SGW-UPF connection, both MME and SGW needs to be upgraded along with LTE eNB to support mobility.
Figure-6 : Single Registration Mode
Figure-7 : Dual Registration mode
2.2.1.2.2. Dual Registration mode
In the Dual Registration mode the UE can connect to both eNB and gNB at the same time. UE decides as to which Radio the UE should latch on to. The overhead of MME communicating to AMF does not exist here. Changes on the core can be minimised with this option.
2.2.2. Impact Analysis
2.2.2.1. Impact on UE
- 5G subscribers will have to get new UEs supporting NR.
- The battery may discharge faster toggling between 4G LTE and NR in the Interworking scenarios.
2.2.2.2. Impact on eNB
- In the standalone deployment, there is no impact on the eNB or EPC.
- In the Interworking mode eNB must be upgraded to support N26 interface to communicate to gNB. The operator will have higher operational costs as they have to maintain both 5G and 4G networks.
2.2.2.3. Impact on core
MME and SGW-U will require an upgrade to communicate with AMF and UPF respectively.
2.3. Option-3/3a/3x
Referred to as 5G NSA E-UTRA-NewRadio-Dual-Connectivity (ENDC), it consists of evolved E-UTRA and NR connected to the EPC. This option allows the operators to launch NR services such as eMBB at an early stage. The NR coverage boosts the User Plane capacity in the areas having high traffic load. Example, shopping malls, stadiums, live concerts etc where the Uplink and Downlink traffic is high. With LTE eNB co-existing with NR further benefits of LTE can be leveraged by providing nationwide continuous coverage and mobility. This is preferred first step towards migrating to 5GS completely.
A tight interworking between NR and E-UTRA is required in this option. It requires NR to be launched on frequencies higher than that being used for LTE and coverage is likely to be smaller than the LTE, especially for the frequencies that are above 6GHz. The radio coverage will have to combine both Low and High frequencies in order to provide both umbrella and hotspot coverage. This is required to cope up with the 5G services having different coverage requirements.
In this option the LTE eNB will be the anchor point for routing the control plane traffic acting as Master-eNB (MeNB) and NR gNB will act as secondary eNB (SeNB). Below figures depicts the control plane and user plane connectivity.
Figure-8 : Control-plane connectivity
Figure-9 : User Plane Connectivity
This option is split into three flavors, Option-3, Option-3a and Option-3x.
Note: Option3/3a have evolved from LTE while Option3x was introduced with 5GS.
2.3.1. Option-3 - Split Bearer
In this Option S1-U connection to SGW is terminated at eNB (MeNB). Depending on the traffic received eNB can decide to route a part of the traffic to gNB. This option can be considered when a huge user data traffic expected.
Figure-10 : Deployment Option-3 – Split Bearer
2.3.2. Option-3a - Secondary Cell Group bearer (SCG Bearer)
In this option the SeNB (gNB) is directly connected to the S-GW in the S1-U interface. enB (MeNB) is not involved in the transport of the User Plane data. User plane traffic is routed directly from gNB. This is an excellent option for the operators who want to keep the LTE and 5G traffic routed distinctly. For Example: voLTE traffic can be routed via eNB and Internet traffic (eMBB) can be routed via gNB.
Figure-11 : Deployment option3 for option(3) and option (3a)
Below figure depicts the Radio Protocol Architecture split bearer and SCG bearer in option 3/3a.
Figure-12 : Radio Protocol Architecture for split bearer and SCG bearer in Option 3/3a
2.3.3. Option-3x - Secondary Group Cell Split Bearer (SCG Split Bearer)
In the option the MME still terminates at the eNB (which means the control plane is still handled by eNB), while the S1-U data is split at the gNB.
Figure-13 : Option3 SCG Split bearer
Figure-14 : Radio Protocol Architecture for SCG split bearer in Option 3x
2.3.4. Impact Analysis
2.3.4.1.Impact on eNB
In order to support Dual connectivity some enhancements may be required at both eNB and gNB. Such as,
- Enhancements to the SeNB (Secondary eNB Modification REQUEST/ACK/REQUIRED/CONFIRM) procedures may be needed to support use case differences between E-UTRA and NR technologies.
- With NR, SCG Split bearer option needs to be supported (Option3x).
- LTE eNB (MeNB) must provide its tunnel endpoint information in SENB ADDITION REQUEST or SeNB MODIFICATION REQUEST message to receive DL data transmission from the gNB;
- gNB (SeNB) must provide its tunnel endpoint information in SeNB ADDITION REQUEST ACKNOWLEDGE or SeNB MODIFICATION REQUEST ACKNOWLEDGE message to receive UL data transmission from the LTE eNB;
- Flow control procedure needs to be applied to the other direction, i.e. LTE eNB signals DL DATA DELIVERY STATUS to the gNB, and the gNB signals DL USER DATA to the LTE eNB.
- Support for using the Global eNB ID or converting to it must be considered.
2.3.4.2. Impact on UE
- Additional support for NR is required, which means User plane protocol stack must be modified to support NR.
- The battery consumption will be higher as the UE must support both NR and E-UTRA.
- Memory consumption will increase due to the combining of NR and eNB for split bearers.
- 5G enabled UE must be backward compatible to support 4G.
Figure-15 : CP protocol stack
Figure-16 : UP Protocol Stack
2.3.4.3. Impact on Core
- AMF and SGW User Plane has to be upgraded to communicate with UPF.
- The launch of a New RAN without a new CN would just increase dependency on legacy EPC,thus creating complex roaming scenarios and limiting business opportunities.
2.4. Option-4/4a
This option represents 5G in NSA mode with both generations of RAT (4G and 5G) connected to 5G core. This option is also referred to as New-Radio-EUTRA-Dual-Connectivity (NRDC). In this option unlike the option-3, EPC is completely replaced by 5GC. The UEs that support 4G only will not be supported anymore with this option. This implies that all the 5G subscribers can fully leverage the benefits of 5G Radio and 5G core.
AT&T has a view that though option-7 is the preferred first step, they will eventually plan to migrate to option2 and/or option4.
In some geographical areas Ex. Rural areas, operators may choose not to invest in deploying NR as, it may not be beneficial. But, 5G Core benefits can be reaped by the LTE subscribers. Since, only 5G subscribers are benefited with this option, the operator may still continue to support 4G subscribers with EPC.
5G NR acts as MeNB and LTE acts acts as SeNB. This option can be further split in to
- Option-4
- Option-4a
2.4.1. Option-4 - Split bearer
In this option the Control plane is handled by MeNB i.e 5G gNB while LTE eNB acts as SeNB.
In this Option User plane connection is terminated at gNB (MeNB). Depending on the traffic received, gNB can decide to route a part of the traffic to eNB. This option can be considered when a huge user data traffic expected.
Figure-17 : Deployment Option-4 – Split Bearer
2.4.2. Option-4a - Secondary Cell Group bearer (SCG Bearer)
In this option the SeNB (eNB) is directly connected 5GC. User plane traffic is routed from both gNB and eNB.
Figure-18 : Deployment Option-4a – SCG Bearer
Figure below depicts the protocol architecture for split bearer and SCG Bearer for option 4/4a.
Figure-19 : Architecture for split bearer and SCG Bearer for option 4/4a
2.4.3. Impact Analysis
2.4.3.1. Impact on UE
Additional support for NR is required, which means User plane protocol stack must be modified to support NR.
The battery consumption will be higher as the UE must support both NR and E-UTRA.Memory consumption will increase due to the combining of NR and eNB for split bearers.5G enabled UE must be backward compatible to support 4G.
2.4.3.2. Impact on the eNB
eNBs will need an upgrade to support NR and 5G core.
2.4.3.3. Impact on Core
A new 5G core must be introduced.
2.5. Option-5
In this option of deployment, the evolved eNB is directly connected to 5G Core. Subscribers can partially leverage the benefits of 5G core with upgraded Radio interface.
This deployment usually exists with option-4.
Since user will be most benefited by moving to NR, this option as SA is less recommended.
Figure-20 : Deployment Option-5
2.6. Option-6
In this option 5G NR is connected to EPC in SA mode. This option most likely is going to exist with option-3 and many operators do not endorse this scenario as SA.
Figure-21 : Deployment Option-6
2.7. Option-7/7a
An immediate path to migrate for the operators from option-3. This option is similar to option-3, with EPC replaced by 5GC. The LTE eNB acting as Master eNB (MeNB) and 5G gNB acting as Secondary gNB (SeNB).
With this option, operators can provide all the 5G eminence to the 5G subscribers. Operators may deploy this option with option3, so that both options co-exist until NR coverage is provided everywhere and all UEs support 5G. With existing LTE network, operators can provide full coverage and mobility services. This Gives flexibility to the operators to selectively upgrade the existing eNB. The operator can consider not to upgrade the eNB to NG-eNB in certain rural areas during initial deployments.
Since the eNB is acting as Master node, the control plane traffic is routed via the eNB, while, the user plane traffic can be routed via both eNB and gNB.
Below figures, depicts user plane and control plane connectivity in this option.
Figure-22: Control Plane Connectivity for Option 7/7a/7x
Figure-23 : User Plane Connectivity for option 7/7a/7x
This option is split into three flavors, Option7, Option7a and Option7x.
Note: Option7/7a have evolved from LTE while Option7x was introduced with 5GS to support SCG Split bearer.
2.7.1. Option 7/7a
Same as Option-4a.
Difference: LTE eNB acts as Master eNB and 5G gNB acts as Secondary eNB.
2.7.2. Option 7x
In this option the NG Control plane terminates at eNB while the User Plane is split in gNB.
Figure-24 : SCG Split bearer in Option7x
2.7.3. Impact Analysis
2.7.3.1. Impact on UE
UEs must be upgraded to support NR and 5GC (to support communication over NAS).
2.7.3.2. Impact on eNB
The eNB must be upgraded to support N2 and N3 interface to support 5GC.
2.7.3.3. Impact on Core
A new 5G core must be introduced.
