What happens when GBR of a VoLTE call cannot be mantained due to lack of radio resources?

Hello Experts,
What happens when GBR of a VoLTE call cannot be mantained due to lack of radio resources?
Let’s sat that admission control allowed 20 VoLTE calls per cell.
Now suddenlty few of them move into bad RF and GBR cannot be fulfilled for them.
What happens to those calls assuming that coding rate is not dynamic (cannot be reduced to 6.6 kpbsec for example)?
As far as I know there is no release of call due to GBR not fulfilled anymore.
But vendors have features: Huawei for example has SRVCC due to VoLTE bad quality in UL or DL.
So if packet loss rate is higher than 60% in either UL or DL for 2 seconds then SRVCC will happen.
Apart from this is someone aware of any other measure that RAN takes when GBR cannot be fulfilled anymore?
Alternatively not only SRVCC due to bad VoLTE quality but also interfreq handover due to low VoLTE quality.

Mainly less bandwidth and TDD are given less preference for VoLTE and in interfreq seen barred too from FDD to TDD.
If multiple carrier are available.

We called them GBR but actually RAN does not guarantee any bit rate.
It works on best effort even for VoLTE.

Because there is voipdlbundling switch too you can switch off in high congestion as your MOS is important than throughout.
Useless switch I have seen its drawback if ON.
Huawei has good feature on VoLTE quality features too like rate control and uplink compensation, continous scheduling and so on.

Yet we see in counters lot of samples with poor and bad quality for VoLTE.

So this are some good feature to cross verify.
Is your ulvoipserviceenhances switch ON?
And one basic check: what’s dltargetbler for VoIP?
Is it zero or 10 recommended.
TTI bundling too threshold create headache for MOS in FDD mainly.

As I know there is new parameter maxgbrtraffic limit introduced in VoLTE starting to keep some % resources reserved for VoLTE, please check it’s value if it there.

Yes but as UE move into more bad RF (poor SINR) it needs lower MCS and more PRBs to sustain the rate.
If there are no such resources what should happen with a VoLTE call?
Keep it without a GBR satisfied or release it due to QoS reasons?

If RTP gap is more than 1 s.
Samsung releases RRC connection and redirect UE to available lower band carrier.

For Uplink scenario few feature tried, VoLTE UL coverage boosting, TTI bundling, Packet segmentation otherwise without feature call can drop.
I see at poor SINR RTP packet flow stop (tool used edat for analysis).

That is the point!
No call is ever dropped due to QoS reason on any vendor.
Only due to RLF.
But not due to QoS.
So you can drag a VoLTE call with 1 kbpsec for hours without releasing it.

RTP packet bytes it show in DL/UL as 0 bytes one of predominant cause for VoLTE call drop with poor SINR, i.e. bye message seen.

Yes, otherwise there would not be a single mute call in network :joy:

Wait, this is happening when rate is 0 kbpsec.
I am speaking about something else 2-3 kbpsec.
And VoLTE call is still there.
So even the lowest codec amr-wb 6.6 kbpsec cannot ensure a good MOS with rate 2-3 kbpsec.
How come those calls are never released due to congestion/qos or some other reason?

I seen bearer reconfiguration.
But very rarely.

Ok, but did you get my point?
Why do we call them guaranteed bit rate when in fact RAN does not guarantee it and keep it even with a lower rate than the GBR rate?

Have you seen in your case?

No, I have never seen one released due to QoS.
Only due to RLF or RTP gaps of 10 seconds.

ERAB modification for GBR is a feature.
Need to enable.

RTP timeout timer generally 20 ms configured at sbc end keeping monitoring of RTP packets drop.

Now 2 conditions:

  1. RRC connection release at poor SINR where chances of bearer reconfiguration,
  2. Or UE send bye due to RTP drop.

Any other reasons seen?

But packets come every 20 msec. How can it be “RTP timeout timer generally 20 ms”?
Maybe 1-2 seconds or 10 seconds?