NSA split bearer Primary Path

5G NR
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1

Hi Experts.
In NSA split bearer, what Primary Path should be: cellgroup 1 or cellGroup 0?

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2

Plz check in RRC connection reconfiguration msg → Nr_rediobearerconfig_r15 → moreThanoneRLC → primaryPath → cellGroup ie

3

Yes, it is moreThanoneRlc.

4

You can select any cellgroup, it’s up to your requirements.

5

But cellGroupid is 1.
And secundarycellgroup is cellgroup1.

6

Can you tell me what is keytouse ie value?
If it’s secondary value then.
Your network is using SCG split bearer

7

Good info. It would make more sense to me next time I look at the logs :blush:

8

That is the point. There is no that info in rrcReconf msg.
So I suppose that is using by default previous key.
So, if keytouse is not secundary, can the primarypath be cellgroup1.

9

[3GPP TS 38.331] keyToUse
Indicates if the bearers configured with the list in this radioBearerConfig is using KeNB or S-KgNB for deriving ciphering and/or integrity protection keys. Network should not
configure SRB1 and SRB2 with S-KgNB and SRB3 with KeNB. When the field is not included, the UE shall continue to use the currently configured keyToUse for the radio
bearers reconfigured with the lists in this radioBearerConfig.

Cell group 1 corresponds to secondary, right?
As per the req, we should be using the master group key when this parameter is missing.

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10

I think the same.
I’m trying to figure out why UEs cannot activate bearer after moving to 5G and after 30 seconds EPS bearer indication is inactive.

11

There are some user plane encryptions done in Direct bearer and Split bearer…these keys are related to that Master for MCG(4G) and Secondary for SCG(5G) in NSA network.
Once the PDCP config is done and moved to RLC these keys are configured, and for Split bearers we have keyto use as Secondary where 5G PDCP layer will split into 5G RLC/PHY and 4G RLC/PHY.

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12

Yes, but in this case PDCP of SCG will use MCG CP and IP key.
This is my understanding.

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13

So you think that this couldn’t cause the bearer inactive status.

14

Yes, this is can not cause, I have checked with keytouse: secondary and cellgroup 1 or 0 combination.

15

Ok thanks.
I suppose that the other is correct too: keytouse primarily and cellgroup1 or 0.

16

Hi Experts.

What is difference between this two NSA config:

DlDataSplitThresholdInBytes,b100,create
DlDataSplitPrimaryPath,PRIMARY_CELL_GROUP

DlDataSplitThresholdInBytes,b100,create
DlDataSplitPrimaryPath,SECONDARY_CELL_GROUP