Can we have VoNR call over FR2 as well in SA?

Hi NR Experts,

Can we have VoNR call over FR2 as well in SA?

If UE support VoNR and it’s IMS registered, then what can be reason still for VoNR1 call setup failure?

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Signal conditions, temporary server issues, congestion, almost any reason that impacted normal IMS/VoLTE calls.

As per my understanding, it is NW preference to initiate EPSFB or VoNR.

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Thanks :+1:

As per understanding EPSFB there if UE do not support VoNR or network do not support VoNR.

EPSFB by redirection or measurement based B1.

Can we have VoNR with FR2 as well?

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VoNR & EPSFB can coexist.

Not sure about this one…


What can be scenario here?

I mean, why UE fall back if able to complete call with VoNR?

One of reason can be poor NR coverage I think. But is it like EPSFB with measurement based B2?

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Similar reasons as CSFB & VoLTE coexisted.

Ranging from Congestion, Capacity to support in particular frequency/band, signal conditions.

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Yes, rightly mentioned.

For VoLTE its seen of call fail then UE try for CSFB.

For EPSFB is there any interface required like n26 etc between MME and AMF.

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3GPP has defined it, but depends on UE (ims-VoiceOverNR-FR2-r15) and vendor that supports or not.

Rightly said!

:+1: Thanks!

EPS Fallback can be done from 5G system to EPS for some reasons:

  • 5G system e.g. 5G core is not ready to support VoNR.
  • UE does not support VoNR.
  • 5G system is ready to support but 5G coverage is not completed.

For the reasons that I mentioned above, EPS Fallback can happen.

EPS Fallback can be done with the following options:

  • Without any measurements, i. e. RwR or blindly.
  • With measurement (UE is configured for doing LTE cells measurements).
  • Based upon PSHO which needs N26 interface.

For measurement based scenario and PSHO, Event B2 can be configured.


Thanks! Very clear now.

For CSFB like we have SG interface between MME and MCS for blind fall back and measurement based CSFB.

For EPSFB for blind fallback is there any interface?

Blindly EPS Fallback, there is no need any interface, just frequency will be given to the UE.

Thanks much appreciated :+1:

Summary, as I mentioned above:

EPS fallback to E-UTRA (LTE) can be done with the following options:

  1. Blind RwR (Release with Redirect)
  2. Measurement-based RwR
  3. Measurement-based PSHO

To reduce the delay to setup the VoLTE call in EPS, EPS Fallback for IMS Voice requires the N26 interface to be supported between EPC and 5GC.

So , N26 interface is one of the requirements for EPS Fallback.

See this (This post will help you to understand better why N26 interface is needed): 5G System (5GS) and 4G system (EPS) interworking - Single-Registration Mode

And for more clarification , I created a post to help you more in case of EPS Fallback: 5GS, EPS Fallback for IMS voice service

Hi. Does EPS fallback is only for continuing VoNR calls?

In case 5G coverage gets weaks or is it during idle mode transition as well for initiating voice call?

Hello, this is used when VoNR is initiated like CSFB:

For more information, you can refer to this post: 5G, Voice over NR (VoNR)

Yes thanks for sharing!

That’s very informative. :clap: