LTE RACH contention based timers

Hi Experts.
In LTE RACH contention based, if UE failed in RRC re establishment message, will it go back to do the same process in timer t311?
Mean searching to new cell?

Yes, correct.

But if timer expires then idle or else it will continue process.
Ue will be released if t311 expires.
So we should keep high.

It has to find an eligible cell within 311 otherwise will go to idle.
Eligible cell means any cell, not LTE only.

Yes, iRAT too.

The bad part is that people tend to fix this timer to t311 to 10 seconds.
Without thinking at UE behaviours with impossible to re-establish call within 10 seconds.

5 sec is enough, Huawei keeps 10.
Trying to avoid drops at expense of user performance.

In fact I am not sure how re-establishment works for VoLTE since it is clear it introduces interruptions.

I think MOS will be very bad.
It’s better to introduce timers QCI wise.
Better to drop VoLTE call than interruptions.

Yes, there are zones where there is an interruption every 20-30 seconds for re-establishments.
This is due to no dominance.
So A3 events cannot happen.

Actually there are cases where seen group id same for GBR and NON GBR.
And threshold are delay let’s say IFHO.
This causes issues in VoLTE.
HO group id I mean.
Real time threshold should be diff for HO.
RTP gap can be avoided unless its a last coverage carrier.

Do you mean to say same HO parameter/threshold for gbr/ngbr qci profile?

Yes, same group id.

Yes it will create problem. For VoLTE.

Okay and about doing again rach in t311.

Will the UE do RAHC within same preamble that we have in first attemt? (when we got rrc failure)?

Second question, when will UE go to idle?
I mean at which case we can have that UE go to idle after RRC re establishment failure?

Upon RLF, the UE will come to Idle mode if the AS security was not activated.
If AS was activated, upon RLF, the UE start the timer T311 and within this timer UE will select a suitable cell.
After reading the System Information, the UE send RACH to this cell and send RRC Connection Reestablishment message starting the timer T301.