VoLTE GBR Service

Dear Experts.
Question about VoLTE GBR Service.

Say we have a cell with 20 VoLTE users all in good RF conditions working fine and PRB occupancy close to 100%.
Suddenly all 20 UEs will move in bad RF so each UE requiring more PRBs due to lower MCS.
I expect no more users admitted on the cell due to not enough GBR resources.
But happens with those 20 existing users that need more PRBs?
Will they use same PRB with a lower quality, reducing codec maybe?
What if codec cannot be changed during call, what happens in this case?
Will cell start to drop VoLTE calls, one by one?
How each vendor is acting in this case?
I know CCO module of SON in this case can shift users to other layers or neighbour cells. But what happens without SON?

I think it depends alot on vendor scheduling algorithm.

  • 1st, eNB will try to allocate more RB for 20 VoLTE UE to maintain its GBR, but it will reduce other PS users throughput, reducing their PRB. VoLTE has higher shceduling priority than PS.
  • 2nd, if can not increase PRB for 20 VoLTE users, eNB may try to negotiate to reduce AMR codec rate, so RB may not need to increase.
  • 3rd, maybe eNB can not maintain GBR for all 20 VoLTE users at that time, some UE may be handover, or even drop.

That’s what I think.

PRB is already at 100% due to 20 VoLTE users.

Why 20 VoLTE users can consume 100% PRB?

It is common in good RF.
Or acceptable RF conditions.
In bad RF an user can consume more than 30 PRBs.

In fact, cell 100% PRB can not only be consumed by 20 VoLTE users.
100 PRB, VoLTE TTI = 20ms, in 20ms, we have 20 * 100 = 2000 PRB
VoLTE users no need to get data every TTI.

You forget RF quality
So if it is bad it will consumes lot of resources.
Ok, this was just an example maybe not 20 VoLTE users let’s say 50.

I think to maintain GBR of all VoLTE users, PS users will be affected.
If just VoLTE users in cells, some UE may be handover or even drop.

Tricky part is that none will be dropped!
I can guarantee you this.
Quality of every user will be degraded but no drop.
For any vendor.

Because in fact cells have VoLTE & PS users, not just VoLTE users.
First eNB try to decrease codec rate, last is must drop.

Yes, idea is that there are no Vol;Te drops due to QoS only due to RLF.
You will nto see VoLTE drops due to Quality.
This is why you have muted calls, silence periods during calls, metallic noises etc.

L.E-RAB.AbnormRel.Cong.VoIP: Number of abnormal releases of activated E-RABs for voice services because of radio resource overload

Have you seen this counter pegging values?

I mean algorithm has releasing VoLTE UE due to congestion, this should be the last choice, may not meet in fact.

I mean why drop them and not interfreq or interRAT them? :slight_smile:

Inter-freq & iRAT HO is selected before release UE, drop is last choice.