Why SRB3 cannot be used in NE-DC?

Hi Guys,
I read that SRB3 can only be used for EN-DC, NGEN-DC and NR-DC.
But cannot be used in NE-DC.
Anyone know the reason?

As of now only EN-DC option 3x and NR-DC option 2 commonly used.
Not sure NE-DC deploy in any network.

Thats fine, I only want theoretical explanation.

My opinion is, SRB3 can be used by 5G signalling protocall stack only (gNB).
4G stack cannot construct SRB3 (By specification?)
NE-DC is only DC where eNB is SN, hence it cannot use SRB3.

SRB 3 is between UE and Secondary node.
SN can be ng-eNB as well.

SRB3: in EN-DC, NGEN-DC and NR-DC, a direct SRB between the SN and the UE.

Yes. Question was: why SRB3 cannot be used in NE-DC?

It is possible that SRB3 is intended only for NR cell in SCG but not LTE cell in SCG.
May be, the designers didn’t want to complicate the LTE requirements.

I also feel the same.

In release 15, for ENDC case for SCG (SN) (NR) 3GPP introduce SRB3.
In which it cantinas 3 msg.
Rrc reconfiguration, RRC reconfiguration complete, and MR (existing SRB1 and SRB 2 doesn’t cantinas this msgs).
Second option 3gpp introduce is SRB1 and SRB2 split bearer (most of the operator using this option).

So here in the case of NEDC, NR will be MCG (MN).
So here SRB1 and SRB2 are a part of NR only.
Both the SRB cantinas all required msg.
Here network will use SRB split configuration only.

Yes here SRB split is only used.

Question was why not SRB3?
Answer may be like eNB stack doesn’t support SRB3?

Yes eNB stack doesn’t support SRB3 msg.