What is the criteria for allocating 5G NR PDCP entity?

Yes, correct.

For LTE, you can user either version, LTE or NR. Sure, if the UE is NR capable.

Nokia document states doing such approach improves the performance, rather than reconfiguring later.

After initial attach, the radio bearer will be attached to the 5G NR PDCP entity if the LTE nodeB supports ENDC ( have X2 links to 5G gnb configured by Operator). This allocation is independent of the status of 5G SCG Physical layer status from 5G gNB.

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ā€œTo reduce the data loss and data duplication during bearer type change without affecting the other MCG bearers of the connection, the data bearer which is eligible to become an SN-terminated split bearer is established in the eNB as MCG bearer with NR PDCP.ā€

There you go.

This should be how your stack look like after, for example, you run out of NR coverage and have PSCELL removed.

There is no image for the scenario before addition, but would be like this.

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Yes, Makes Sense.

Let me explain how samsung does this PDCP selection.

  1. Once 5G NSA UE is attached to LTE, initially only 4G PDCP anchor is configured for all the bearers.
  2. Once there is decision for SgNB adition, anchor point is changed from 4G PDCP to NR PDSCP. Which can only done by Intra cell HO or bearer release/add methods. This steps involved data loss also.
  3. It is also decided for which QCIs NR PDCP will be used for. For example, for QCI1 and QCI5 same 4G PDCP will be used, but for QCI8,9 NR PDSC will be used.
  4. When NR is relased by A2 event configued for example, above process is reversed, i.e. QCI8,9 are not anchored by 4G PDCP.
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Sounds about the same for Ericsson.
Intra-cell HO.
One thing we must differ is between PDCP version and the stack view, as showed in the picture Iā€™ve sent.
You can use a NR version of PDCP while running purely on LTE.

You are absolutely right. LTE stack can have both PDCP version as below.

image

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Thank you for the info.

So for clarifying: "Once there is decision for SgNB adition, anchor point is changed from 4G PDCP to NR PDCP. "
This decision would be based on B1 event?
And this applies for Ericsson & Samsung as per above dscussions and this 5G PDCP entity selection is independent of B1 event in Nokia & Huawei.
Here it depends on the UE capability for NSA.

Is my understanding correct?

I think 5G PDCP entity selection for Huawei is done at call setup (after security mode complete) for 5G capable UEs.

Correct, selecting the PDCP version is based on UE Capability.
If the UE is NSA capable, go for NR PDCP, if not, LTE.
The decision to configure the B1 is also based on capability, surely, the difference is that Samsung and Ericsson will only go through the intra-cell ho, this, changing the PDCP version, if the UE reports an NR neighbor.
Assuming measurement based addition.

With Huawei it doesnā€™t even matter if the LTE cell is anchor to a NSA cell or not (because thereā€™s no B1 event configuration for that LTE cell) it is simply configured the 5G PDCP entity.

But the LTE cell should be an anchor with X2 to 5G, right?
Because pure eNB site may not need 5G PDCP, right?
Otherwise the eNB may be ng-eNB?

If it would be an anchor to NSA you would see B1 event configured, right?
In Drive Test we donā€™t see it.
So call is established with 5G PDCP, then 3-5 HOs in LTE, then it comes a 4G cell that has NSA and where B1 event is delivered and NSA is started.

B1 will be seen only if measurement reports shows 5G, right?
For that if the UE is in cell edge of NSA B1 events wonā€™t be triggered so that even if LTE is NSA configured you might not see B1.

Am I right?

Not exactly. B1 config comes via 4G , thereā€™s no coverage hole in 4G.

I am talking about B1 measurement configuration not about measurement report B1.

Oh, ok.
I was refering to measurement report.

Interesting discussion regarding vendor differences.
My 2 cents:
SgNB addition and SCG configuration are 2 different procedure that can happen together or separately.
SgNB addition (in option 3X) transfers PDCP from LTE to NR
SCG configuration allows for split bearer and SCG bearer options. Without SCG, only MCG bearer is available

Hello Guys,

Just to understand the above thread do we know a typical case when NR PDCP will be used with LTE RLC, i.e SN terminated LTE MCG bearer in place of SN terminated split bearer?
Thanks