Drop Call when moving from VoLTE site to LTE site

Hi Experts.

Any idea about Drop Call when moving from VoLTE site to LTE site?

Admin note: this post was updated with image below.

Check SRVCC.


The problem can be just on SRVCC?

Or there are other parameters?

Do you mean HO to an LTE site without VoLTE support?


In this case I don’t think SRVCC will be triggered.

Because there is no HO triggered to 3G.

And I expect call drop because VoLTE is not supported on target cell.

I am commenting from IMS Core persperctive, not a radio nw expert.

That means no way drop will happen between VoLTE site and non VoLTE site.

We are having too many HOs in VoLTE which is effecting the call quality.

What can be done to improve that is there any way?

If there is some feature / parameter on radio side that might prevent 4G-4G HO when target cell doesn’t support VoLTE and there is an active qci1, that would help.

But if not a smart way to manage HO, yes there is no way to avoid call drop.

Rather than preventig ho between these sites.

To do what you want in this case, either convert this to CSFB then go out from the VoLTE site (which will cause service interruption) or go through SRVCC to continue this call on 3G/2G.

Check out attached signal flow:

Yes there is: increase filter coefficient, increase time to trigger. But this means you will stay longer on old cell and your call will be interfered anyway.

You need some optimization to impose a clear dominance.

You cannot trick interference by playing with parameters.

You can trick KPIs, call drop rate but not quality.

Not necessarily.

eNB filters out target cells which don’t support volte services (this is controllable through switches in some vendors).

Now as UE moves out of coverage of VoLTE service, it will perform SRVCC.