EN-DC Failures due to Single UE

RAN
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1

Hi Experts.

Need your opinion on one issue related to EN-DC failures:

Post SgNBadditionreqACK, eNB sent RRC RECFG to UE and UE responded back with RRC RECFG CMP msg, right after receiving this message,

eNB sent another RRC RECFG message to UE to release one of B7 SCELL; UE again responded w ith RRC RECFG CMP msg.

After that eNB sent another RRC RECFG message to UE to release remaining B7 SCELL; this time UE did not respond to eNB instead did re-establishment to target cell with cause of “reconfig failure”

Now the question: if at first UE sent RRC RECFG CMP message then why it is instructing UE to release B7 list?

UE supports band combinations before releasing B7 cells and also if UE release both band 7 cells it would have still supported remaining band combination.

PS: This scenario keep repeating on single UE and results high nr of EN-DC failures.

EN-DC Failures due to Single UE
EN-DC Failures due to Single UE733×727 68.8 KB

2

Any 1 of the reason is leading to send rrc rrconfig reqt.

  • Case 1 : When radio link failure happened

  • Case 2 : when Handover failure happened

  • Case 3 : when mobility from E-UTRA failure happened

    Revert back to the configuration used in the source PCell, excluding the configuration configured by the physicalConfigDedicated, mac-MainConfig and sps-Config;

    Initiate the connection re-establishment procedure as described in How it works and Common UE side Process

  • Case 4 : when integrity check failure indication was received from lower layers

  • Case 5 : when RRC connection reconfiguration failure happened (UE cannot comply to the configuration set by RRC Connection Reconfiguration message)

3

For that single UE where this issue is being experienced, every time, enb sending RRC RECFG to release B7 SCELL.

Just updating that if UE release both band7 cells, it wont comply with config sent by enb therefore UE is doing re-establishment with cause of reconfig failure; which is fine.

Question still remains same that why is eNB always instructing same UE every time to release Band 7 SCELLs though UE responded with RRC RECFG CMP msg initially.

4

May be UE has multiple SCCs of band 7 and nw is releasing them one by one.

I might be wrong but if this could be a case then multiple Reconfigs will come and if in second Reconfig nw is releasing already released band 7 cell then UE will trigger reestablishment.

5

There’s no event triggered.

It’s just eNB is sending updated reconfig to UE to release band 7 scells.

This happens all the time to only one type of UE

UE configured with b13 pcell + band 2 + band 7 + band 7 (scells).