How gNB declares Radio Link Failure?

Hello 5G Experts.

How gNB declares Radio Link Failure?

For vendors Nokia and Ericsson?

What are the mechanism?

1 Like

I think any system RLC maxrtransimission decides gNB RLF.

1 Like

Or max csi missed.

1 Like

Not only maxrlc retransmission but also N310, T310, N311, T311.

1 Like

N310, N311, T310, T311 … all these counters and timer works on UE side only.

1 Like

Yes, you are right. :+1:

I have not noticed you are interested on gNodeB side…

1 Like

Thanks. Do you know the exact parameters / threshold?

And what is the expectations of gNB from UE?

I wanted some deep drive in whole process from RLF to recovery.

1 Like

Check RLF based parameters in RRC max retarsimission 4/8/16/32

Ideally the operators set this as 32 times

Are you talking about tPoll retransmit max?

Or maxRetxThreshold?


But this is again used by UE to declare RLF.

Normally UE used to get in RRC setup/reconfiguration for RLC-AM.

eNB/gNB Will declare the RLF it’s it does not receive response from UE after maxretrasimission.

Yes but when Maximum retransmission reaches on RLC let say 32 times in that case UE will understand channel condition is not reliable and will declare RLF.

How gNB will declare RLF?

gNB declare the RLF by sending UE context release.

UE context Release process comes after RLF declaration from gNB side?


Yes. It should have reason also why UE context release initiating by eNB/gNB.

Max retranx you can refer RRU Setup where it will be mentioned the value vary from 1 to 32

The Physical Layers of the UE Can use the CSI-RS to generate in-Sync & Out-of-Sync Indications.
The Physical Layers of the UE generates and reports an Out of Sync indication to RRC layer when the Radio link quality of all of the monitored RS is worst then Qout

gNB declares RLF when there is UL sync loss from Ue . If it doesn’t rcv any message in Ul then it will release the Ue context , then Ue will try to reestablish the RRC connection to best available network.

Think when UL sync is lost.

At RRC level N313 T313 timers.

When there is a broken link b/w the RFU/RRU and the BBU.

It could either be due to faulty CPRI fiber cable, BB port, SFP module, radio, or the BBU itself.

Once CSI missed gNodeB declare RLF and release connections.