Timeout mean it will calculate RTP packet if 0 bytes for 20 ms.
(Not sure, value 20ms may be wrong, maybe 20s). IMS guys working over sbc can comment.
GBR has higher priority then Non-GBR.
Network will try to maintain its resources even if it has to kick out NonGBR users.
Also I think GBR is EPS bearer attribute.
RAN tries to provide necessary quality, if it cannot it will obviously do other actions.
Yes but from E2E user perspective, when RAN cannot do anything more, why do we keep such a GBR that is under-performing?
I fully understand and agree with this. But even so there are cases when GBR cannot be maintained even if we allocate 50 PRBs to a volte call. We should simply IRAT such a call due to QoS reasons or drop it.
Now none of this is happening. Operators drag VoLTE voice calls no matter of RF conditions and there’s full of metallic voices, distortioned voice, one way audio, mute calls, etc.
Normally, UE is configured to send RTCP & RTCP-XR pkts in UL to report the quality of DL RTP flow.
IMS should change the codec to lower bandwidth or activate features like TTI bundling accordingly with the SIP UPDATE to match the UE RF condition, right?
This is a design issue. 3GPP never thought about a cause like this" if QoS cannot be maintained for more than 5 seconds then RAN must release the call with cause congestion".
Just walk 5 minute in the end user shoes. Would you like to have voice calls with current quality that is today?
It will be RLF, why congestion? Qci1 can fail due to RLF.
RLF is so bad that it means no communication at all.
I am speaking about something else here, I am speaking when there is communication but is very poor to have a decent voice call.
Also do you understand that any RLF and call re-establishment introduces a significant voice gaps of more than 1-2 seconds?
Is this part of the Quality of Service we want to deliver to end user?
We all want green KPIs and end user pays a hard price for our green KPIs.
I mean end user is in the middle of an important voice call.
How many call re-establishment it takes before he gets upset and moves to competition?
3, 5, 10 call-reestablishments?
I would say maximum 5.
It’s always in seconds. (20 seconds in this case).
Uh, that’s a lot of time to wait for a drop call in VoLTE!
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Thanks 
I forgotten unit. 
User disconnect the call before it expires 
And then it becomes normal release.
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Yes, sometimes I faced that phone is frozen. So user is even more upset!
Effectively phone is frozen till RTP timer expires.
You need to remove the battery and restart phone.
It happened to me in poor RF something like 6-7 years ago.
We used to chase short voice calls that are normally released and re-initiated by users with same A and B party.