ENDC prep fail reject but zero sgnb change addition attempt

5G NR
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1

Hi Experts.
Half ENDC attempts are showing ENDC prep fail reject in that eNodeB, but there is zero sgnb change addition attempt.
What can be tne reason?
ENDC failing due to sgnb addition reject by enb as fail counter reasons.

2

The SgNB Add Reject message shall contains the cause value for reject. One can determine the possible cause based on the cause value and some are listed below.

Cause values as “Transport resource not available”: Issue at 5G NR side as transport resource not available, these transport resource includes availability of X2-U link between eNB and gNB and S1-U link availability between gNB and 4G Core.

Cause values as “No radio resource available”: 5G The number of users in the cell is insufficient. The gNB ID is duplicate or other resources of the 5G are abnormal (for example, no available SRS resources are available).

Check this: 5G NR NSA Network Access Issues and Possible Root Cause - Techplayon by @Tech_Playon. There causes are given.

3

There is no erab 5G attempt seen.
Nothing defined after LTE attach, I guess.

4

UE can trigger the SCG failure in following condition:

  • SCG radio link failure.
  • Failure of SCG reconfiguration with sync.
  • SCG configuration failure for RRC message on SRB3. SRB3 is control plane between UE and gNB.
  • SCG Integrity Failure.
  • Exceeding the maximum uplink transmission timing difference.

This things also mentioned I think.
Expiry of T310 in Pscell.

5

There is no 5G erab happening it’s only doing ENDC with half success.

6

RA Problem indication.

7

Rlc retx condition.

8

if LTE network does not initiate the SgNB_ADD, check NBRs definition & Status X2 interface between 4G and 5G.

1 Like
9

Hi Experts,
What can be the reason for Addition reject with cause “protocol: semantic-error( )”
We traced the Add rejections and more of them are with this cause.
Thank you in advance,
Rado