RLF cause as PDCP UL release in UE LTE logs

4G LTE
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1

Hi All,
Getting RLF cause as PDCP UL release in UE LTE logs.
Any pointers on possible cause for this?

2

May be because max RLC retransmission in UL.

3

Checked RLC retransmissions, it’s okay.

4

Ok. But I heard this RLF cause first time.

5

If it is RLF then is it due to Radio or Handover.
You can try to increase t310.
And check PDCP Discard Time and eNodeB and UE max threshold.

6

RLF can be due to below reasons only:

  1. At L1
  2. At MAC
  3. At RLC layers

Due to Ho failures.
RLC layer can be due to maxretxthreshold-> Check value
PDCP layer RLF not seen.
Tdiscard will not lead to RLF at PDCP layer.

7

It’s not a Handover scenario, and Radio conditions also perfect.

8

Yes PDCP wil not affect RLF.

9

Where exactly did you checked this cause? In what message?

Try corelating your RLF instance with below categories:

UE side RLF declaration-
Based on RLF declaration timers N310, T310 etc
Based on Max RLC retransmission, typically 32
RACH failures problems, typically 64 MSG 1 transmissions
RRC reconfiguration failures

eNB side RLF declaration-
Based om Max RLC retransmission, typically 32

10

This from QCAT:
Payload String = RFL Count since RRC Connected = 1, RLF Count since LTE Active = 52, RLF Cause = PDPDUL_RELEASE

11

Have you seen reestablishment request with same cause?
I think it must show other failure.

12

Nope, it’s fresh connection after that.

13

What is last RRC message in DL that UE has received?

14

RRC reconfiguration message.

15

HO command was included in it?
If RLF is exactly after receiving RRC reconf msg and HO command is included in it, it can be due to HO failure or RRC reconfiguration failure.
Otherwise its purely RRC reconf failure.

Is this frequent behaviour with this UE?

16

No, it’s not.

17

It’s RRC reconf failure (RLF after RRC Reconf msg).
Check what was included in RRC reconf message, something might not be supported/handled by UE.

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18

Thanks, I will check that.

19

Hi Mr Pritam, did you find out root cause of this issue?I am also facing same issue in QC chipset device

20

Hi @Raju_Gupta,

Yes, in the RRC reconfig message there was an invalid codec specified which was not being supported by the UE. Hence, PDCP UL release and finally RLF caused.

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