5G SA mobile capable phones VoNR

Hi, can someone help me out. Imagine you have a 5G SA VoNR capable device that wishes to register itself amounst a 5G network that NOT support VoNR?

Will the device still be capable to use 5G SA data or will it fallback to 5G NSA/4G?


Yes, a 5G SA VoNR capable device will still be able to connect to a 5G network that doesn’t support VoNR.

In this scenario, the device will fallback to a mode it can mutually connect with the network, which will likely be:

  • 5G NSA (Non-Standalone): This is a more common 5G deployment currently, where the 5G signal relies on an existing 4G LTE core for control functions. Most 5G SA VoNR devices are also backwards compatible with 5G NSA.

  • 4G LTE: If the network doesn’t even support 5G NSA, the device will fall back to the most compatible option, which is 4G LTE.

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Hi, thanks for the reply.

I have an additional question.

Is it correct that the behaviour will be the same for the data, meaning that 5G SA data will not be allowed and that the mobile will fallback to 5G NSA?

No, the behavior for data access on a 5G SA network that doesn’t support VoNR isn’t guaranteed to be a complete fallback to 5G NSA


an extra question?

In a case of a 5G SA capable device (voice & data)?
Is the voice mapped on a predefined slice like we have in 4G (IMS predined configuration on the mobile)? So more or less mapped IMS DNN (APN) on the default slice.

If this is the case, can a mobile still use another slice for the data part? (without the URSP feature).

Will Apple/SAMSUNG allow to have 2 concurrent sessions on the default and another one on a different slice at the SAME TIME?

Thx for the support.

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In 5G SA, voice calls typically don’t use a pre-defined slice like 4G. The device can use the default slice for both voice and data, or leverage network slicing for data on a separate slice (without URSP) depending on operator configuration. Apple/Samsung allowing concurrent default and separate slice sessions is device and network dependent.

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Do you mean a mapping on a different DNN that is mapping on a different slice?
Can we achieve this as well via a static policy that is pushed via a PCEF when the enduser gets connected to the netwerk?