VoNR call initiate in 5G SA but cell is down

[ankgitm]

Hi 5G Experts, I have 1 query.

For VoNR call, if at time of VoNR call initiate 5G SA cell is down. Then what happen to call?

Drop by UE out of service or it’s EPSFB to LTE?

[ran_core_consultant]

If the cell is down, how is UE connected to this cell?

[RFSpecialist]

@ankgitm

Drop by UE out of service or its EPSFB to LTE?

How can it be EPSFB without any signalling when 5G SA cell is down?

[ankgitm]

So it’s limited service and call will drop, as of no EPSFB?

[sadanandk2]

I can see 2 scenarios here.

• Assuming no other NR cell available there, UE will perform fresh attach at LTE, and its straight away call drop.

• Assuming some other NR cell available there, UE will perform re-establishment to new cell.
  There is bearer preservation functionality at Core side.
  If it is enabled, then VoNR bearer can be resumed at new cell, and VoNR call continues.
  Of course this has to happen within some timer gets expire at Core level.
  Packet loss, muting at other part are expected consequences.

[ankgitm]

@RFSpecialist

How can it be EPSFB without any signalling when 5G SA cell is down?

I’m thinking same so it’s basically call drop scenario.

@sadanandk2

I can see 2 scenarios here.

• Assuming no other NR cell available there, UE will perform fresh attach at LTE, and its straight away call drop.
• Assuming some other NR cell available there, UE will perform re-establishment to new cell.
  There is bearer preservation functionality at Core side.
  If it is enabled, then VoNR bearer can be resumed at new cell, and VoNR call continues.
  Of course this has to happen within some timer gets expire at Core level.
  Packet loss, muting at other part are expected consequences.

Assuming no NR SA cell in coverage area only single NR SA cell and LTE cells in surrounding.
Seems it will be call drop.
Earlier thinking EPSFB possible or not.