5G Deployment Option-3/3a/3x

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Hi Guys today we are learning about 5G deployment options, if you want to know more about other 5G deployment option please click here

Option 3: EN-DC (EUTRA-NR Dual Connectivity)

Option 3 represents a network having both LTE and NR radio access, but using only the EPC core of LTE to route the Control signals. In this option, LTE is used as the control plane anchor for NR, and both LTE and NR are used for user data traffic.(user plane).

It could also be called as Non-Standalone (NSA) NR in Evolved Packet System.

The only difference between Options 3 and 3A is based on whether the user plane data is sent to NR directly or via the LTE RAN.

This standardization was concluded in 3GPP Rel-15. This is a possible first step in the migration towards 5G-SA.
This option will be most attractive for operators which have early deployments of 5G NR access systems in areas where legacy eNB and EPC are operational. 

In this option, the operators do not need a 5G Core. In the early 5G stages of deployment, Option 3/3a/3x will be the likely choice for many operators.
As this approach is tied to LTE, it is important not to disrupt the existing network. Operators have the options of deploying dual connectivity for data like high throughput in NR downlink and best coverage in LTE uplink, meanwhile voice traffic will be fully on LTE.                                                                                                                   

To support EN-DC, the legacy LTE network needs to be upgraded to 3GPP release 15 which will be called eLTE.

As specified in TS 36.300 and TS 36.423, in Option 3/3a, Dual Connectivity (DC) should be reused as baseline so that EPC is not impacted. Therefore, for the Xx interface between gNB and LTE eNB, the procedures and protocols would remain similar to those of DC, while minor enhancements cannot be ruled out.

As defined in TS 36.423, the Xx-U will have all the functionalities of X2-U for LTE DC operation. No impacts are foreseen to S1 procedure with the support of Option 3/3a/3x.

Option 3 requires routing 5G data through eNBs,
Option 3A can’t support dynamic switching between LTE and 5G.

Option-3/3a/3x are transparent to MME and P-GW, and translate to an E-RAB modification procedure at MME.

• Option-3 — Traffic is split between 4G and 5G at eNodeB.
• Option-3a — Traffic is split between 4G and 5G at EPC (S-GW).
• Option-3x — Traffic is split between 4G and 5G at 5G cell.

Option 3: 

In the plain option 3, all uplink/downlink data flows to and from the LTE part of the LTE/NR base station, i.e. to and from the eNB. The eNB then decides which part of the data it wants to forward to the 5G gNB part of the base station over the Xx interface. In simple terms, the 5G gNB never communicates with the 4G core network directly!

Salient features:
▪ UE will be connected to both 5G NR and 4G LTE.
▪ For Option 3 Control Plane relies on EPS LTE S1-MME interface and LTE RRC Control.
▪ For Option 3 User Plane might split bearer

 Key advantages:
▪ Reuse of EPC & S1
▪ Low investment (only for 5G BS gNB)
▪ Possible reuse of VoLTE with minor upgrade

Up gradations required:
▪ Increased complexity in 5G UEs (EN-DC capable)
▪ Upgrade eNB to connect to gNB via Xx/Xn interfaces
▪ Backhaul requirements of 5-30 ms between gNB and eNB

Option 3A: 

In this option, both the LTE eNB and the 5G gNB can directly talk to the EPS core network but they cannot directly talk with each other over the Xx (X2) interface. This means that a single data bearer cannot share the load over LTE and NR. For example, VoLTE voice traffic for a user is handled by LTE while his Internet traffic is handled by the 5G part of the base station. It would be difficult to implement this scenario if the devices keep moving in and out of 5G network coverage continuously.

Note: As per TS37.340, for dual connectivity between LTE and NR, X2-C interface will be used for Option 3a.
Option 3X:

Option 3X is a combination of 3 and 3A.

In this configuration, user data traffic will flow directly to the 5G gNB part of the base station. From there, it is delivered over the air to the mobile device. A part of the data can also be forwarded over the X2 interface to the 4G eNB part of the base station and from there to the UE. Slow data streams (Low Data), e.g. VoLTE bearers with a different IP address than that used for Internet access can be directly delivered from the core network to the 4G eNB part of the 4G/5G base station. The advantage is that the 5G upgrade of the base station is likely to have the much better performing IP interface so it is better suited to handle the higher data rates that can only be reached with a 4G/5G Non-Standalone network deployment.

Option-3X provides robust coverage in higher frequencies and aggregated peak bit rate of LTE and 5G for lower frequencies.

Option-3X also provides near zero interrupt time LTE-5G mobility.
Option-3X provides allows voice in LTE without using RAT fallback.
This configuration can be used in scenarios where LTE coverage reach is superior to that of NR and thus leverages EPC.

In this configuration, the LTE eNB will act as the Master and will have control over which S1-U bearers are handled by radio of LTE or NR. Based on instructions from LTE eNB, MME will inform S-GW where to establish S1-U bearers, i.e. LTE or NR. If NR radio quality falls below a certain threshold,  S1-U bearer towards NR may be either split at NR and sent entirely over Xx to LTE or a PATH SWITCH may be triggered where all S1- U will go to LTE eNB.


  1. Quick Overview.. Interesting.!
    So I believe UE can differentiate Nw implementation options based on the type of Bearer setup..?
    • Option-3 — Traffic is split between 4G and 5G at eNodeB. --> MN terminated Split bearer.
    • Option-3a — Traffic is split between 4G and 5G at EPC (S-GW) --> SN terminated SCG only bearer
    • Option-3x — Traffic is split between 4G and 5G at 5G cell. --> SN terminated Split bearer

  2. This comment has been removed by a blog administrator.

  3. Thank you for the quick interview, which is very nice.
    And I have below doubt in UL split case. If you have idea could you please give some light on this?
    When UE hits splitting of data condition, then
    How much of data portion sends towards NR and how much of data portion towards LTE?


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