Two VoLTE UE trying to call but receiving CS-Paging

Dear Experts,
Have you already faced a case where an VoLTE UE generates a VoLTE call for another VoLTE UE, but the paging that comes from the Core is a CS-Paging generating a CSFB?
The two mobile are in a benchmarking test.
That means both are under the same RF condition.
Vendor is Huawei.

So CSFB is happening at incoming end?

Yes, correct.

It may be that your CSFB is having high priority instead of VoLTE as CS priority is defined high.

VoLTE-3G_CS.
During the DT just some calls are hapenning like that.

So are there high VoLTE users in that area, may be.
As some calls are happening, can you check Erlang and VoLTE traffic KPI?
And just check VoLTE priority if is set high or not.

Do You mean VoLTE resources congestion?
But in this case the first paging should be a PS-VoLTE, no?

Yes, first should be PS paging for VoLTE.
Can you check ROHC and VoLTE priority defined?
And there are at least 4 byte in VoLTE calls if this is less then too issue happens.
We have 40 bytes in IPV4 and 60 in IPV6, we need to have atleast 4 byte for VoLTE after enabling ROHC.

This priority would be in each network node?
Usually QCI-1 has high priority.

There is parameter as VOIP priority.

What is QCI priority for HO (in LST CELLQCIPARA) for QCI1?

Sorry, but at this MO I just found two parameters related to priority:

  • QCI Priority For Handover
  • QCI Priority For DRX

But maybe you are referring to HO_USE_VOIP_FREQ_ALLOWED?
But I did not get the relation with CSFB.

What’s the percentage of calls happening like this?
At incoming end.

This evaluation had been done during the Drive Test and on 3 calls it happened.
Considering DT as a sampling the objective is to understand the reason for having a perspective of that cluster users.

So the percentage is very very less.

Thinking on DT perspective, yes it is.
But without knowing the root cause it is tough to have a perspective for the rest of the users.

Yes, that’s right.

But the tip about capacity of the cells where that happened was a good one.
If you think in something more please let me know. :wink:

Yes, during that time happened you can check Erlang and VoLTE traffic.
And your PRB utilisation and VoLTE prb utilisation.

The CCE load is also important.

Yes CCE too.

There is one feature i think name is like VoLTE user prior access, but it’s for MO calls.
If some counters are failing and fall under some scenario then can be enabled basically.
But if you have this counter pegging then it is done.