Secondary Node Addition Failure

5G NR
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1

Hi Experts.

I am not able to understand this paragraph.

As per I know RACH happens after the SGNB addition is completed.

Secondary Node Addition Failure

The procedure to add a seconday node may fail. One cause of failure is an unsuccessful random access on the NR cell. Random access for SN addition is supervised by the timer GNBDUFuntcion.Rrc.t304, which is set in the gNodeB and signaled to the UE in the RRC Reconfiguration message. If t304 expires before the random access is successfully completed, then the UE reports a radio link failure (RLF) to the eNodeB.

Any comments?

2

I think it depends on UEs.

Some UEs send RRC reconfig cmp just after receiving the RRC reconfig msg, hence SgNb add complete is sent back to gNB and RACH happen after that.

3

No. RACH is performed for sgnb addition only.

You might got confused with Sgnb addition request and response procedure between eNB and Sgnb over X2 interface?

4

As per this, RACH is happening after SgNB addition is completed.

In SgNB addition SR kpi also we don’t consider the RACH SR.

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5

The red circled flow is SgNB addition preparation success, enB point of view.

But UE point of view SgNB addition / SCG addition is after RACH success only.

Your KPI simply not covering RACH.

6

Okay… understood :+1:

This RACH procedure is Contention based or Contention free?

7

Mostly contention free.

But it can be contention based also.